[Federal Register Volume 63, Number 32 (Wednesday, February 18, 1998)]
[Rules and Regulations]
[Pages 8298-8321]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-3898]
[[Page 8297]]
_______________________________________________________________________
Part IV
Department of Transportation
_______________________________________________________________________
Federal Aviation Administration
_______________________________________________________________________
14 CFR Parts 1 et al.
Improved Standards for Determining Rejected Takeoff and Landing
Performance; Final Rule Proposed Revisions to Advisory Circular--Flight
Test Guide for Certification of Transport Category Airplanes; Notice
Federal Register / Vol. 63, No. 32 / Wednesday, February 18, 1998 /
Rules and Regulations
[[Page 8298]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Parts 1, 25, 91, 121, and 135
[Docket No. 25471; Amendment Nos. 1-48, 25-92, 91-256, 121-268, 135-71]
RIN 2120-AB17
Improved Standards for Determining Rejected Takeoff and Landing
Performance
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final rule.
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SUMMARY: This action amends the airworthiness standards for transport
category airplanes to: revise the method for taking into account the
time needed for the pilot to accomplish the procedures for a rejected
takeoff; require that takeoff performance be determined for wet
runways; and require that rejected takeoff and landing stopping
distances be based on worn brakes. The FAA is taking this action to
improve the airworthiness standards, reduce the impact of the standards
on the competitiveness of new versus derivative airplanes without
adversely affecting safety, and harmonize with revised standards of the
European Joint Aviation Requirements-25 (JAR-25). These standards,
which affect manufacturers and operators of transport category
airplanes, are not being applied retroactively to either airplanes
currently in use or airplanes of existing approved designs that will be
manufactured in the future.
EFFECTIVE DATE: March 20, 1998.
FOR FURTHER INFORMATION CONTACT:
Donald K. Stimson, FAA, Airplane & Flightcrew Interface Branch, ANM-
111, Transport Airplane Directorate, Aircraft Certification Service,
1601 Lind Avenue SW., Renton, WA 98055-4056; telephone (425) 227-1129,
facsimile (425) 227-1320.
SUPPLEMENTARY INFORMATION: An electronic copy of this document may be
downloaded using a modem and suitable communications software from the
FAA regulations section of the FedWorld electronic bulletin board
service (telephone: 202-512-1661) or the FAA's Aviation Rulemaking
Advisory Committee Bulletin Board service (telephone: 800-FAA-ARAC).
Internet users may reach the FAA's web page at http://www.faa.gov
or the Federal Register's webpage at http://www.access.gpo.gov/su__docs
for access to recently published rulemaking documents.
Any person may obtain a copy of this final rule by submitting a
request to the Federal Aviation Administration, Office of Rulemaking,
ARM-1, 800 Independence Avenue, SW., Washington, DC 20591, or by
calling (202) 267-9680. Communications must identify the amendment
number or document number of this final rule.
Persons interested in being placed on the mailing list for future
notices of proposed rulemaking and final rulemaking and final rules
should request from the above office of copy of Advisory Circular No.
11-2A, Notices of Proposed Rulemaking Distribution System, that
describes the application procedure.
Small Entity Inquiries
The Small Business Regulatory Enforcement Fairness Act of 1996
(SBREFA) requires the FAA to report inquiries from small entities
concerning information on, and advice about, compliance with statutes
and regulations within the FAA's jurisdiction, including interpretation
and application of the law to specific sets of facts supplied by a
small entity.
The FAA's definitions of small entities may be accessed through the
FAA's web page (http://www.faa.gov.avr/arm/sbrefa.htm), by contacting a
local FAA official, or by contacting the FAA's Small Entity Contact
listed below.
If you are a small entity and have a question, contact your local
FAA official. If you do not know how to contact your local FAA
official, you may contact Charlene Brown, Program Analyst Staff, Office
of Rulemaking, ARM-27, Federal Aviation Administration, 800
Independence Avenue, SW, Washington, DC 20591, 1-888-551-1594. Internet
users can find additional information on SBREFA in the ``Quick Jump''
section of the FAA's web page at http://www.faa.gov and may send
electronic inquiries to the following internet address: 9-AWA-
[email protected]
Background
These amendments are based on notice of proposed rulemaking (NPRM)
93-8, which was published in the Federal Register on July 8, 1993 (58
FR 36738). In that notice, the FAA proposed amendments to 14 CFR parts
1, 25, 91, 121, and 135 to improve the standards for determining the
accelerate-stop and landing distances for transport category airplanes.
The FAA received over 100 comments from 22 different commenters on the
proposals contained in NPRM 93-8. As a result of these comments, the
FAA has modified some of the original proposals.
As explained in NPRM 93-8, the operator of a turbine-powered
category airplane must determine that the runway being used, plus any
available stopway or clearway, is long enough to either safely continue
or reject the takeoff from a defined go/no-go point. The go/no-go point
occurs while the airplane is accelerating down the runway for takeoff
when the airplane reaches a speed known as V1.
The assure that the takeoff can be safely continued from the go/no-
go point, the length of the runway plus any clearway must be long
enough for the airplane to reach a height of 35 feet by the end of that
distance, even if a total loss of power from the most critical engine
occurs just before reaching the V1 speed. This distance is
commonly referred to as the accelerate-go distance.
In case the pilot finds it necessary to reject the takeoff, the
runway plus any stopway must be long enough for the airplane to be
accelerated to the V1 speed and then brought to a complete
stop. This distance is known as the accelerate-stop distance.
The choice of V1 speed affects the accelerate-go and
accelerate-stop distances. A lower V1 speed, corresponding
to an engine failure early in the takeoff roll, increases the
accelerate-go distance and decreases the accelerate-stop distance.
Conversely, a higher V1 speed decreases the accelerate-go
distance and increases the accelerate-stop distance. When V1
is selected such that the accelerate-stop distance is equal to the
accelerate-go distance, this distance is known as the balanced field
length. In general, the balanced field length represents the minimum
runway length that can be used for takeoff.
The V1 speed selected for any takeoff depends on several
variables, including the airplane's takeoff weight and configuration
(flap setting), the runway length, the air temperature, and the runway
surface elevation (airport altitude). The takeoff performance and
limitation charts in the Airplane Flight Manual (AFM) are developed in
accordance with the FAA airworthiness standards in subpart B of the
Federal Aviation Regulations (FAR), part 25--``Airworthiness Standards:
Transport Category Airplanes,'' using data gathered during
comprehensive flight tests completed as a part of the FAA's approval of
the airplane's type design.
Part 25, subpart B, also prescribes the FAA airworthiness standards
for determining the length of runway required for safe landing under
various airplane and atmospheric conditions. Landing performance charts
must be published in the AFM, and are used by
[[Page 8299]]
the operator to determine whether a particular runway is long enough
for landing.
The FAA, through the general operating rules contained in parts 91,
121, and 135, requires operators to use the appropriate performance and
limitation charts published in the AFM to plan their takeoffs and
landings.
In NPRM 93-8, the FAA proposed amendments to several sections of
parts 25, 91, 121, and 135 concerning the methods for determining and
applying the takeoff and landing performance standards for turbine-
powered transport category airplanes. Also, the FAA proposed to amend
part 1, which contains terms and abbreviations used in the FAR, to add
a definition of the term ``takeoff decision speed'' and an explanation
for the abbreviation ``VEF.''
The proposed amendments retained the fundamental principle that the
pilot should be able to either safety complete a takeoff or bring the
airplane to a complete stop, even if power is lost from the most
critical engine just before the airplane reaches a defined go/no-go
point. This principle has formed the basis of the takeoff performance
standards required for the type certification of turbine-powered
transport category airplanes since Special Civil Air Regulation No. SR-
422, effective August 27, 1957. The amendments proposed in NPRM 93-8
were intended to provide a more rational method to take into account
the various operational aspects affecting the takeoff distance. By the
phrase ``more rational method,'' the FAA means a method that explicitly
addresses the specific elements affecting the takeoff distance, rather
than providing for critical conditions by applying more restrictive
standards to all takeoffs.
If the takeoff performance standards are made more restrictive,
longer distances are needed for takeoff. However, the operator cannot
change the length of the runway (although a longer runway, if
available, could be used). Instead, the operator must usually reduce
the airplane's takeoff weight in order to shorten the distance needed
for takeoff. The more restrictive the takeoff performance standards
are, the more takeoff weight may have to be reduced to be able to
operate from a particular runway.
To reduce the airplane's takeoff weight, the operator must either
reduce the amount of fuel to be carried, or reduce the number of
passengers or amount of cargo to be transported. Since the amount of
fuel to be carried is dictated primarily by the route being flown, the
operator's only option may be to reduce the number of passengers or
amount of cargo to be transported. When the number of passengers or
amount of cargo must be reduced for a given flight, the airplane
operator can suffer a loss of revenue.
Amendment 25-42, which became effective on March 1, 1978, revised
the takeoff performance standards to make them more restrictive. Prior
to Amendment 25-42, variations in pilot reaction time were provided for
in the AFM accelerate-stop distances by adding one second to the flight
test demonstrated time interval between each of the pilot actions
necessary to stop the airplane. Typically, there are three such
actions. The pilot reduces the power, applies the brakes, and raises
the spoilers. Adding one second between each of these actions results
in a total of two seconds being added to the time taken by the flight
test pilots to accomplish the procedures for stopping the airplane. In
calculating the resulting accelerate-stop distances for the AFM, no
credit was allowed for any deceleration during this two-second time
period.
The revised standards of Amendment 25-42 required the accelerate-
stop distance to include two seconds of continued acceleration beyond
V1 speed before the pilot takes any action to stop the
airplane. This revision resulted in longer accelerate-stop distances
for airplanes whose application for a type certificate was made after
Amendment 25-42 became effective. Consequently, turbine-powered
transport category airplanes that are currently being manufactured
under a type certificate that was applied for prior to March 1, 1978,
have a significant operational economic advantage over airplanes whose
type certificate was applied for after that date. This competitive
disparity resulting from applying different performance standards
created a compelling need to amend the takeoff performance standards of
part 25 without adversely affecting safety. In addition, operational
experience indicated a need to specifically address the detrimental
effects of worn brakes and wet runways on airplane stopping
performance.
Amendment 25-42 was a broad brush approach, applying to all
takeoffs, to increase the required accelerate-stop distance. This broad
brush approach did not explicitly account for many of the important
operational factors that may affect takeoff performance. For example,
the standards did not distinguish between dry and wet runways, nor were
the effects of worn brakes taken into account. Wet runways and worn
brakes typically result in longer accelerate-stop distances than with
new brakes on a dry runway. By requiring wet runway performance to be
determined and included in the AFM, and by requiring the use of worn
brakes to determine the airplane's stopping capability, the proposed
amendments would provide additional accelerate-stop distance for the
conditions in which it is specifically needed in operational service.
Because wet runways and worn brakes would be specifically addressed
in the revised standards proposed in NPRM 93-8, the FAA also proposed
to replace the two seconds of continued acceleration beyond
V1 with a distance equal to two seconds at the V1
speed. The distance equal to two seconds at constant V1,
while shorter than that resulting from the continued acceleration
beyond V1 required by Amendment 25-42, is a distance margin
that must be added to the accelerate-stop distance demonstrated during
flight testing for type certification. The FAA intends for this
distance margin to take into account the variability in the time it
takes for pilots, in actual operations, to accomplish the procedures
for stopping the airplane.
Amendment 25-42 required the two seconds of time delay to be
applied prior to the pilot taking any action to stop the airplane. This
more restrictive approach assumes that the airplane reaches a higher
speed during the accelerate-stop maneuver and, therefore, results in a
longer distance than the distance equal to two seconds at constant
V1 speed. Inserting the time delay before the pilot takes
any action to stop the airplane, however, does not accurately reflect
the procedures that pilots are trained to use in operational service.
V1 is intended to be the speed by which the pilot has
already made the decision to rejected the takeoff and has begun taking
action to stop the airplane. The time it takes for the pilot to
recognize the need for a rejected takeoff, which occurs before
V1 is reached, is considered separately within the
airworthiness standards. Therefore, the amendments proposed in NPRM 93-
8 were intended to more accurately reflect the rejected takeoff
procedures taught in training and the intended use of the V1
speed.
In summary, the purpose of the amendments to the takeoff
performance standards of parts 25, 91, 121, and 135, as proposed in
NPRM 93-8, was to more rationally reflect the operational factors
involved and reduce the impact of the standards on the competitiveness
of new versus derivative airplanes. More restrictive standards were
proposed for takeoffs from wet runways. In addition, the proposed
standards would require accelerate-stop distances to be
[[Page 8300]]
determined with brakes that are worn to their overhaul limit. Lastly,
the two seconds of continued acceleration beyond V1 speed
would be replaced by a distance equal to two seconds at V1
speed.
In NPRM 93-8, the FAA also proposed to amend the landing distance
standards of part 25 to account for worn brakes. The FAA proposed this
change to be consistent with the proposal for taking worn brakes into
account for the takeoff accelerate-stop distances. Because airplanes
generally require more distance to take off than to land, the allowable
landing weight is rarely limited by the available runway length.
Therefore, the proposed landing distance rule change was not expected
to have a significant effect on the number of passengers or amount of
cargo that can be carried.
International Harmonization of Airworthiness Standards
For more than ten years, the FAA has been cooperating with the
Joint Aviation Authorities (JAA) of Europe to promote harmonization
between the FAR, particularly the airworthiness standards, and the
European Joint Aviation Requirements (JAR). The aircraft certification
authorities of 23 European countries are members of JAA. An annual
meeting is held between FAA senior management officials and senior
management officials of the JAA member authorities to identify
technical subject areas where cooperation is needed to promote greater
harmonization between the FAR of the United States and the European
JAR. A large portion of these meetings have been open to the public. A
comprehensive study of this activity was completed by Professor George
A. Bermann, Columbia University School of Law, in May 1991 as a
consultant to the Administrative Conference of the United States
(ACUS). A copy of Professor Bermann's final report to ACUS, titled:
``Regulatory Cooperation with Counterpart Agencies Abroad: The FAA's
Aircraft Certification Experience,'' dated May 1991, is included in the
docket. Based on Professor Bermann's report. ACUS has confirmed the
administrative appropriateness of this effort and has indicated strong
support for this activity in their Recommendation 91-1, titled
``Federal Agency Cooperation with Foreign Government Regulators,''
adopted June 13, 1991.
At the annual FAA/JAA meeting in June 1989, the FAA and JAA
discussed the competitive disparity caused by the differences between
the takeoff performance standards applied to airplanes that met the
later standards of Amendment 25-42, as compared with airplanes that
were only required to meet the takeoff performance standards that
preceded Amendment 25-42. Even though the airplane types were
originally type certificated at different times, thus allowing the use
of different amendments, both groups of airplanes are continuing in
production and both are competing for sales and for use over some
common routes. Airplanes whose designs were type certificated to the
standards introduced by Amendment 25-42 could be penalized in terms of
the number of passengers or amount of cargo they can carry over a
common route, even though the airplane's takeoff performance might be
better from a safety perspective than a competing airplane design that
was not required to meet the later standards. Currently, most of the
transport category airplane types that have been required to meet the
later standards of Amendment 25-42 were designed and manufactured
outside the U.S. (mostly in Europe). These airplanes are competing for
sales against airplanes that were designed and manufactured in the U.S.
that were not required to meet the standards of Amendment 25-42. This
situation has led to claims by a major European manufacturer of
transport category airplanes that this disparity in the airworthiness
standards has created an unfair international trade situation affecting
the competitiveness of their airplane types of a later design.
At the June 1990 annual meeting, the FAA and JAA agreed to jointly
review the current takeoff performance standards and their
applicability with respect to airplanes currently in use and airplanes
produced in the future under existing approved designs. The goal was to
reduce the inequities described above without adversely affecting
safety. The study consisted of two parts: First, the current takeoff
performance standards were reviewed to determine if they were too
restrictive; and second, the merits of making the resulting standards
apply retroactively were considered for both airplanes currently in use
and airplanes produced in the future under existing approved designs.
The FAA and JAA also agreed to initiate substantively the same
rulemaking within their respective systems to harmonize the European
and U.S. takeoff performance standards for transport category
airplanes.
The FAA concluded that the takeoff performance standards of part 25
could be made more rational, and thus less restrictive overall, without
adversely affecting safety and proposed to amend the standards
accordingly. However, considering the safety benefits and available
economic impact information, the FAA could not support a recommendation
to make the standards proposed by NPRM 93-8 retroactive to either
airplanes currently in use or future production airplanes of designs
that have already been type certificated. If additional information to
support making these proposed standards retroactive became available at
a later date, the FAA proposed to review such information and determine
if further rulemaking would be appropriate.
In March 1992, the JAA issued its Notice of Proposed Amendment
(NPA) 25B, D, G-244: ``Accelerate-Stop Distances and Related
Performance Matters'' to amend the takeoff performance standards of
JAR-25. The amendments proposed in NPRM 93-8 were substantively the
same as the amendments proposed by the JAA NPA for JAR-25.
Discussion of the Proposals
In NPRM 93-8, the FAA proposed the following rule changes:
1. Replace the two seconds of continued acceleration beyond
V1 (mandated by Amendment 25-42) with a distance margin
equal to two seconds at V1 speed;
2. Require that the runway surface condition (dry or wet) be taken
into account when determining the runway length that must be available
for takeoff; and
3. Require that the capability of the brakes to absorb energy and
stop the airplane during landings and rejected takeoffs be based on
brakes that are worn to their overhaul limit.
Proposal 1
The FAA proposed to amend the method of determining the accelerate-
stop distance prescribed in Sec. 25.109 by replacing the two seconds of
continued acceleration after reaching V1 with a distance
equal to two seconds at V1 speed. This proposal would reduce
the accelerate-stop distance that must be available for a rejected
takeoff because the airplane would be assumed to begin stopping from a
lower speed (from V1, rather than from the speed reached
after two seconds of acceleration beyond V1). The FAA's
intent was to replace the most costly aspect of Amendment 25-42 with a
requirement that closely represents the pre-Amendment 25-42 criteria of
Sec. 25.109, as applied to the certification of recent U.S.-
manufactured airplanes.
Proposal 2
The FAA proposed to amend Sec. 25.105 to require that airplane
takeoff performance data be based on wet, in
[[Page 8301]]
addition to dry, runways. Section 25.1587(b) would be amended to
require that performance information for wet runways be included in the
Airplane Flight Manual (AFM). Sections 91.605, 121.189, and 135.379 of
the operating rules would be amended to require that wet runways be
taken into account when determining the runway length that must be
available for takeoff, if wet runway performance information exists in
the AFM. Thus, this rule would apply only to airplane designs for which
the application for type certification occurs after the amendment
becomes effective, and to those previously certificated airplane
designs for which the manufacturer chooses to re-certify to the amended
standards.
Section 25.109 would be revised to provide the details of how the
accelerate-stop distance would be calculated for a wet runway. The FAA
proposed the following approach to determining the wet runway takeoff
performance: (1) Take into account the reduced braking force due to the
wet surface; (2) permit performance credit for using available reverse
thrust as an additional stopping force; and (3) permit the minimum
airplane height over the end of the runway after takeoff to be reduced
from 35 feet to 15 feet. This approach would reduce the risk of
overruns during rejected takeoffs on wet runways while retaining safety
margins for continued takeoffs similar to those required for dry
runways.
The reduced braking force available is the most significant
variable affecting the stopping performance on a wet runway. The FAA
proposed to revise Sec. 25.109 to specify that the wet runway braking
force would be one-half the dry runway braking force, unless the
applicant demonstrated a higher wet runway braking force. Under this
proposal, the one-half of the dry braking force level would apply
regardless of whether the dry runway braking force is limited by the
torque capability of the brake (which is the friction force generated
within the brake) or the friction capability of the runway surface.
Although it can be argued that the torque capability of a brake is
independent of the runway surface condition, the proposed use of this
simple relationship between wet and dry runway braking capability would
depend on using the one-half dry relationship throughout the braking
phase.
Data published in Engineering Science Data Unit (ESDU) 71026,
entitled ``Frictional and Retarding Forces on Aircraft Types--Part II:
Estimation of Braking Force,'' shows that the relationship between wet
and dry braking coefficient varies significantly with speed. At high
speeds, the wet runway braking coefficient is typically less than one-
half the dry runway braking coefficient. At low speeds, the wet runway
braking coefficient is typically more than one-half the dry runway
braking coefficient. Used over the entire speed range for the stopping
portion of a rejected takeoff, however, the wet runway braking
coefficient can justifiably be approximated as one-half the dry braking
coefficient. The ESDU report is included in the docket.
Under this proposal, Sec. 25.109 would also be revised to permit
the use of available reverse thrust when determining the accelerate-
stop distance for a wet runway. ``Available'' reverse thrust was
interpreted as meaning the thrust from engines with thrust reversers
that are operating during the stopping portion of the rejected takeoff.
Credit for reverse thrust was included in the proposal because the most
significant variable that affects the stopping performance on a wet
runway, reduced braking friction, was also included as part of the
rational approach to wet runway rejected takeoff.
On dry runways, the FAA proposed to explicitly deny credit for
reverse thrust when calculating the accelerate-stop distance. This
proposal would codify current FAA policy. Although reverse thrust
should and probably would be used during most rejected takeoffs, the
FAA believes that the additional safety provided by not accounting for
reverse thrust in calculating the accelerate-stop distance on a dry
runway is necessary to offset other variables that can significantly
affect the dry runway accelerate-stop performance determined under the
current standards. For wet runways, credit for reverse thrust would be
permitted because taking into account the reduced braking force
available on the wet surface, as proposed in this notice, greatly
outweighs the effects of these other variables. Examples of variables
that can significantly affect the dry runway accelerate-stop
performance include: runway surfaces that provide poorer friction
characteristics than the runway used during flight tests to determine
stopping performance, dragging brakes, brakes whose stopping capability
is reduced because of heat retained from previous braking efforts, etc.
The FAA proposed to revise Sec. 25.113 to allow the distance
required for a continued takeoff from a wet runway to include taking
off and climbing to a height of 15 feet, rather than the height of 35
feet required on a dry runway. This lower screen height (which is the
height of an imaginary screen that the airplane would just clear with
the wings in a level attitude when taking off or landing) would reduce
the balanced field length V1 speed, thereby reducing the
number of high-speed rejected takeoffs on wet runways. The FAA
considers lowering the screen height to 15 feet to be an acceptable
method of reducing the risk of overruns on wet runways because of the
similarity to current rules when operating from dry runways that have a
clearway. The minimum height permitted over the end of the runway for
current dry runway takeoffs may be 13 to 17 feet, depending on the
airplane, when a clearway is present. In addition, a 15-foot minimum
screen height and vertical obstacle clearance distance has been allowed
for many years by the United Kingdom Civil Aviation Authority for wet
runway operations without any problems being reported.
The combination of a clearway with the proposed 15-foot screen
height for wet runways could result in a minimum height over the end of
the runway of near zero (i.e., liftoff very near the end of the
runway), if clearway credit were to be permitted for wet runways in the
same manner that it is currently permitted for dry runways. The FAA
considers this situation to be unacceptable. The possible presence of
standing water or other types of precipitation (e.g., slush or snow)
and numerous operational factors (e.g., late or slow rotation to
liftoff attitude) emphasize the need to provide more of a safety margin
than would be present if liftoff were permitted so near the end of the
runway. Therefore, the proposed Sec. 25.113 would not permit the
combination of clearway credit and a 15-foot screen height. The FAA
proposed to modify Sec. 25.113, however, to ensure that the presence of
a clearway does not result in requiring longer runway lengths than if
there were no clearway.
In addition to the reduced screen height for wet runways, the
minimum vertical distance required between the takeoff flight path
defined in Sec. 25.115 and obstacles (e.g., trees, hills, buildings,
etc.) would be reduced by a corresponding amount. To accomplish this,
the FAA proposed to revise Sec. 25.115 to state that the takeoff flight
path shall be considered to begin at a height of 35 feet at the end of
the takeoff distance.
This revised definition of the takeoff flight path would apply
equally to dry and wet runways, even though the height of the airplane
at the end of the takeoff distance (i.e., the screen height)
[[Page 8302]]
for wet runways is proposed to be only 15 feet. The effect of this
proposal would be to make it possible to use the flight path
information currently contained in the AFM even if the runway is wet.
Because the screen height would be reduced from 35 feet to 15 feet for
a wet runway, the height of an airplane at any point in the flight path
will therefore be approximately 20 feet lower from a wet runway than
from a dry runway. Under this proposal, the airplane's actual height
over obstacles would be reduced by approximately 20 feet when taking
off from a wet runway.
Under the current regulations, the airplane's flight path must be
higher than any obstacles by a combination of an increment of height
and an increment of gradient (i.e., the slope of the flight path).
Although this proposal would reduce the height increment by
approximately 20 feet, the gradient increment would be unchanged. As
the distance from the end of the takeoff distance increases, the
gradient increment provides an increasingly greater portion of the
total height difference between the airplane and the obstacle.
Therefore, the effect of reducing the height increment over obstacles
by 20 feet diminishes as the distance from the end of the takeoff
distance increases.
Proposal 3
The FAA proposed to amend Sec. 25.101(i) to require that
accelerate-stop and landing distances must be determined with all the
airplane brakes at the fully worn limit of their allowable wear range.
Section 25.735 would be revised to require that the maximum brake
energy capacity rating must be determined with each brake at the fully
worn limit of the allowable wear range. In addition Sec. 25.735 would
be amended to add a requirement for a flight test demonstration of the
maximum kinetic energy rejected takeoff with not more than 10 percent
of the allowable brake wear range remaining.
Miscellaneous
Additionally, the FAA proposed to add one new definition and one
new abbreviation to part 1, Definitions and Abbreviations.
As a result of their special investigation of rejected takeoff
accidents, the National Transportation Safety Board (NTSB) recommended
that the FAA clearly define the term ``takeoff decision speed''
(V1) in part 1. This recommendation is contained in the
NTSB's Special Investigative Report, ``Runway Overruns Following High
Speed Rejected Takeoffs,'' published on February 27, 1990.
Concurring with the NTSB recommendation, the FAA proposed to add a
definition of takeoff decision speed to Sec. 1.1 in order to remove
apparent confusion over the meaning of this term. The FAA's proposed
definition was intended to make it clear that the decision to reject
the takeoff, indicated by the pilot activating the first deceleration
device, must be made no later than V1 for the airplane to be
stopped within the accelerate-stop distance.
The abbreviation VEF is used in several places within
part 25. The FAA proposed to amend Sec. 1.2 to add the definition of
VEF, which currently appears in Sec. 25.107(a)(1).
VEF is the speed at which the critical engine is assumed to
fail during takeoff.
As stated previously, the FAA did not intend to apply these
proposed amendments retroactively to either airplanes currently in use
or future production airplanes of designs that have already been
approved. However, manufacturers or operators of these airplanes may
elect to comply with these proposed amendments by a change to the type
design. The benefits of the revision to the time delay criteria of
Sec. 25.109 would then be available to relieve the economic burden
imposed by Amendment 25-42. The proposed amendments to take into
account the effects of wet runways and worn brakes must also be
included in such a recertification. The FAA expects that, for airplanes
whose certification basis includes Amendment 25-42, most applicants
will elect to comply with this proposal because it will be economically
beneficial for them to do so.
Discussion of the Comments
The FAA received over 100 comments from 22 different commenters
regarding the proposals presented in NPRM 93-8. The commenters include
airplane pilots, manufacturers, operators, and the associations
representing them, foreign airworthiness authorities, and another
agency of the U.S. government. Because of the increasing emphasis
placed on international harmonization of the airworthiness standards,
and because the JAA issued substantively the same proposals to amend
JAR-25, the FAA also received many comments from foreign and
international sources.
In general, the pilots, and the airworthiness authorities of Canada
and the Netherlands oppose the proposed amendments unless the FAA
imposes the new standards retroactively. Conversely, the airplane
manufacturers and operators generally support the proposals as long as
they are not imposed retroactively. The JAA strongly supports the
proposals, but also believes that these requirements should be imposed
retroactively. The association representing European manufacturers
supports applying the proposed standards to new derivatives of existing
approved designs as well as to completely new airplane designs.
Another issue that generated strong contrasting views concerns the
distance needed to align an airplane on the runway for takeoff.
Typically, airplanes enter the takeoff runway from an intersecting
taxiway. The airplane must then be turned so that it is pointed down
the runway in the direction for takeoff. FAA regulations do not
explicitly require airplane operators to take into account the runway
distance used to align the airplane on the runway for takeoff. The
commenters who support retroactivity also support amending the
regulations to require operators to take this runway alignment distance
into account. Those who oppose retroactivity also oppose proposals to
require taking into account the runway alignment distance.
In NPRM 93-8, the FAA stated that ``with the safety benefits and
economic impact information available at this time, the FAA cannot
support a recommendation to make the standards proposed by this notice
retroactive to either airplanes currently in use or future production
airplanes of designs that have already been type certificated.'' This
conclusion was reached after a review of the estimated costs and the
potential benefits that would result from applying the proposed
standards retroactively and mandating that operators take into account
the runway alignment distance.
It should be noted, however, that one part of the proposed
standards has effectively already been imposed retroactively. The FAA
has issued airworthiness directives (AD's) concerning brake wear limits
for every FAA-certificated transport category airplane with a maximum
takeoff weight of over 75,000 pounds. These AD's ensure that the brakes
on these airplanes, even when fully worn, can absorb the energy from a
maximum energy rejected takeoff.
In addition to the economic impact of retroactively applying the
proposed standards, the FAA was influenced by the increasing emphasis
on international harmonization of the airworthiness standards.
Retroactivity of the proposed standards and the requirement to take
runway alignment distance into account, had the FAA decided to proceed
with these provisions, would have been
[[Page 8303]]
accomplished through revisions to the operating rules of the FAR. At
the time NPRM 93-8 was being developed, the JAA lacked operating rules
with which to impose these requirements. Although the introduction and
justification sections of JAA NPA 25B, D, G-244 discussed an intent to
apply the standards retroactively, and to require that runway alignment
distance be taken into account, the JAA lacked a regulatory mechanism
for doing so. Therefore, the proposed standards would not have been
harmonized had the FAA proposed such amendments to the part 91, 121,
and 135 operating rules.
Shortly thereafter, the JAA published NPA OPS-2, containing
proposed JAR operating rules for commercial air transportation (JAR-OPS
1). In this NPA, the JAA proposed to retroactively require operators to
take into account the performance effects of wet runways and runways
contaminated by slush, snow, ice or standing water, and to require
operators to apply adjustments for runway alignment distance. NPA OPS-2
did not address retroactive application of the proposed requirements
related to worn brakes. The JAR-OPS 1 final rule, which retained the
proposals noted above, was issued by the JAA on May 22, 1995. It
becomes effective on April 1, 1998, for operators of airplanes with a
maximum takeoff weight of over 10,000 pounds or a maximum approved
seating capacity of 20 or more passengers.
Due to the controversial nature of the issues of retroactivity and
runway alignment distance, the FAA has decided to: (1) Proceed with the
proposed rules without requiring retroactive application of these
standards or adding a new requirement concerning runway alignment
distance, and (2) recommend that the issues of retroactive application
of these standards and runway alignment distance be added to the FAA/
JAA harmonization work program. Except in the treatment of these two
issues, the final rule adopted by this amendment is completely
harmonized with the applicable JAA standards. These two issues reflect
differences between the FAA and JAA operating rules; the applicable
airworthiness standards of part 25 and JAR-25 are completely harmonized
by this amendment and a corresponding amendment to JAR-25.
The harmonization work program is the formal method developed by
the FAA and the JAA to harmonize relations and policies. Tasks on the
harmonization work program are assigned to FAR/JAR harmonization
working groups in accordance with the respective rulemaking procedures
of the FAA and the JAA. For the FAA, these tasks are assigned to the
Aviation Rulemaking Advisory Committee (ARAC).
The ARAC was established to provide advice and recommendations to
the FAA on all rulemaking activity. There are over 60 member
organizations on the committee, representing a wide range of interest
within the aviation community. Meetings of the committee are open to
the public, except as authorized by section 10(d) of the Federal
Advisory Committee Act. For issues on the harmonization work program,
the ARAC assigns members, who work on behalf of the FAA, to the FAR/JAR
harmonization working group. Although working group meetings are
generally not open to the public, working group task assignments are
published in the Federal Register, and all interested parties are
invited to participate as working group members. Working groups report
directly to the ARAC, and the ARAC must concur with a working group
proposal before that proposal can be presented to the FAA as an
advisory committee recommendation. After an ARAC recommendation is
received and found acceptable by the FAA, the agency proceeds with the
normal public rulemaking procedures.
Most of the commenters who oppose the proposed rulemaking also
claim that the proposals would degrade the level of safety provided by
the current standards. Specifically, these commenters oppose the
proposal to replace the two seconds of continued acceleration beyond
V1 with a distance margin equal to two seconds at
V1 speed (Proposal 1), because it would allow an increase in
the maximum allowable takeoff weight when that weight is limited by the
length of the runway. Although the FAA agrees with the commenters on
the effect of this particular proposal on takeoff weight limits, and
discussed this effect in NPRM 93-8, the FAA disagree that safety is
degraded when this proposal is considered in combination with the other
proposals presented in NPRM 93-8.
In addition to Proposal 1, the FAA proposed other amendments that
would make the current standards more stringent. As explained in NPRM
93-8, the purpose of the FAA proposals was to present a more rational
approach of explicitly providing for the specific elements affecting
takeoff performance, rather than the broad brush approach represented
by the two seconds of acceleration beyond V1. The FAA
considers the proposed standards for worn brakes and wet runways, which
the current standards do not explicitly address, to significantly
improve takeoff safety. Combined with Proposal 1, the proposed
amendments provide an equivalent or higher level of safety than the
current standards.
Depending on whether the runway is wet or dry and on the particular
airplane's stopping capability with worn brakes, the maximum allowable
takeoff weight for a given runway length could end up being either
increased or decreased under the proposed standards. Although its
effects are variable, the FAA estimates that Proposal 1 would reduce,
on average, the runway length needed for takeoff by 150 feet. For
airplanes equipped with typical steel brakes, the proposed worn brake
requirements would add an average of 150 feet to the runway length
needed for takeoff. The FAA estimates that the proposed wet runway
requirements would result in an average increase of 220 feet in the
runway length required for takeoff when the runway is wet. It should be
emphasized that these estimates are average effects that can vary
considerably depending on the airplane type and the specific takeoff
conditions. For example, airplanes equipped with carbon brakes or
certain heavy-duty steel brakes, usually will be uaffected by the worn
brake requirements because these brakes provide the same stopping
capability in the worn condition as the new condition. (The proposed
worn brake requirement represent an important safety improvement,
however, regardless of whether this improvement comes from taking into
account a loss in brake capability, or because the requirements act as
an incentive to provide brakes that do not suffer this loss in
capability.)
Along with this rulemaking effort, the FAA also participated in a
joint FAA/industry team to produce the Takeoff Safety Training Aid.
This training aid, first made available in August 1992, represents the
findings of the team relative to training and procedural actions that
could be taken to increase takeoff safety. The goal of the training aid
is to minimize the probability of rejected takeoff accidents and
incidents by: (1) Improving the ability of pilots to take advantage of
opportunities to maximize takeoff performance margins; (2) improving
the ability of pilots to make appropriate go/no-go decisions; and (3)
improving the ability of crews to effectively accomplish the rejected
takeoff procedures. Simulation trials and in-depth analyses of takeoff
accidents and incidents were used to develop the training aid material.
The FAA urges operators to use the Takeoff
[[Page 8304]]
Safety Training Aid in their qualification and recurrent aircrew
training programs. The FAA is convinced that adoption of this material
will further improve safety during the critical takeoff phase of
flight.
The FAA received a large number of comments on the proposed
definition of takeoff decision speed (V1), including its
relationship to the broader subject of the process by which the pilot
recognizes a failure, decides to reject the takeoff, and acts on that
decision. One commenter submitted several documents as additional
supporting material, including a detailed study of pilot reaction times
during rejected takeoff accidents. This commenter, accompanied by
several others, believes that the proposed standards inadequately
provide for the time it takes the average pilot to complete the
recognition, decision, and reaction process. Other commenters support
the FAA proposal, and some of these commenters also offered suggestions
to further clarify the purpose of the V1 speed.
The diversity displayed in the comments illustrates a great deal of
misunderstanding and disagreement regarding the definition and use of
the V1 speed. In general, inconsistent terminology used over
the years in reference to V1 has probably contributed to
this confusion. As noted by the commenters, V1 has been
referred to at various times as the critical engine failure speed, the
engine failure recognition speed, and the takeoff decision speed.
Special Civil Air Regulation No. SR-422, effective August 27, 1957,
originally referred to V1 as ``the critical engine failure
speed.'' These same standards, which were later recodified into part
25, defined the accelerate-stop distance as the distance to accelerate
to V1, and then to stop from that speed. Although an
allowance was required for any time delays that may reasonably be
expected in service, SR-422 did not explicitly state where or how the
time delays should be introduced relative to V1. For
certification purposes, the FAA considered V1 to be the
speed at which the pilot took the first action to stop the airplane.
Time delays for recognition and reaction to that failure were applied
prior to V1, and delays in accomplishing each subsequent
action for stopping the airplane were applied after V1.
Allowing for the time delays, the actual engine failure was therefore
assumed to occur prior to V1.
With Amendment 25-42, effective March 1, 1978, the FAA amended the
airworthiness standards to clarify and standardize the method of
applying these time delays. V1 was referred to as the
``takeoff decision speed,'' which turned out to be ambiguous in that it
could be interpreted to mean either the beginning or the end of the
pilot's decision process. The preamble to Amendment 25-42, however,
states that ``V1 is determined by adding to VEF
[the speed at which the critical engine is assumed to fail] the speed
gained with the critical engine inoperative during the time interval
between the instant at which the critical engine is failed and the
instant at which the test pilot recognizes and reacts to the engine
failure, as indicated by the pilot's application of the first retarding
means during accelerate-stop tests.'' This same definition was codified
as Sec. 25.107(a)(2). Not only is V1 intended to occur at
the end of the decision process, but it also includes the time it takes
for the pilot to perform the first action to stop the airplane.
The FAA requires applicants to demonstrate, by flight test, the
time intervals between VEF and V1, and between
each subsequent action taken by the pilot to stop the airplane. FAA
pilots and engineers witness and participate in these tests, which must
include at least six rejected takeoffs. Because the test pilots know
that they are going to reject the takeoff, human factors literature
refers to this process as a simple task. In actual operations, the
rejected takeoff maneuver is unexpected, and is referred to as a
complex task. In consideration of this complex task, the time intervals
measured during certification flight tests are increased when the
accelerate-stop distances published in the AFM are calculated. These
additional time increments are not intended to allow extra time for
making a decision to stop after passing through V1. Their
purpose is to allow sufficient time (and distance) for a pilot, in
actual operations, to accomplish the procedures for stopping the
airplane.
The first adjustment is made to the time interval between
VEF and V1. During the certification flight
tests, the pilot expects to reject the takeoff and reacts very quickly.
To take this into account, the time interval used to calculate the AFM
accelerate-stop distances must be the longer of either the demonstrated
time or one second. This standard has been applied to the certification
of every turbine-powered transport category airplane since the late
1960's, and the FAA has not proposed to change it.
The second adjustment concerns the time increment applied after
V1. The method of determining this adjustment has varied,
but the objective has always been the same--to provide enough time and
distance for a pilot to accomplish the procedures for stopping the
airplane. Prior to Amendment 25-42, a one-second increment was added to
the time interval between each pilot action occurring after
V1. For most transport category airplanes, the rejected
takeoff involves three separate pilot actions. The pilot applies the
brakes, reduces the thrust or power, and raises the spoilers. The
applicant defines the order in which the actions occur, but must
demonstrate that the resulting procedures do not require exceptional
skill to perform. Since the test pilot's first action determines
V1, there are typically two pilot actions occurring after
V1. Therefore, two seconds of additional time (and the
resulting distance) were added to the time intervals determined by the
certification flight tests.
Amendment 25-42 changed the method of applying these time
increments. The provisions added by Amendment 25-42 require the AFM
accelerate-stop distance to be calculated by inserting a two-second
time increment after V1, but before the pilot takes the
first action to stop the airplane. During this two-second time
increment, the airplane continues to accelerate. No further time
increments are added to the time intervals between the actions taken by
the pilot to stop the airplane.
It is important to note that Amendment 25-42 did not change the
certification flight test procedures. The two-second time increment is
applied analytically during the calculation of the AFM accelerate-stop
distances, not by directing the pilot to delay action for two seconds
after V1 during the rejected takeoff flight tests.
The proposal presented in NPRM 93-8 would change the method of
applying this two second time increment to a method similar to that
existing prior to Amendment 25-42. However, the proposed method uses a
distance increment rather than a time increment, to ensure that no
credit is taken during this time period for system transient effects
(e.g., engine spindown, brake pressure ramp-up, etc.). The distance
increment is equal to the distance traversed in two seconds at the
V1 speed. Unlike the pre-Amendment 25-42 method, this
distance increment cannot be reduced when fewer than three pilot
actions are used in the rejected takeoff procedures (e.g., for
airplanes using automated systems that take the place of one or more of
the usual pilot actions). The FAA considers the distance traveled in
two seconds at V1 speed to be the minimum acceptable
[[Page 8305]]
distance allowance needed to provide for the element of surprise and
other operational factors missing from the certification flight test
demonstrations.
As long as there are no more than three pilot actions needed to
accomplish a rejected takeoff, the accelerate-stop distance is
determined using the demonstrated time intervals between pilot actions
with no additional time or distance increments applied. For each
additional pilot action beyond the first three actions, however, a one-
second time (and distance) increment must be added to the demonstrated
time interval for that action.
The FAA disagrees with those commenters who believe that the
proposed standards inadequately provide for the time it takes the
average pilot to complete the recognition, decision, and reaction
process. Not only does the FAA require applicants to determine by
flight test the length of time needed for the pilot to complete this
process, but this demonstrated time interval is also increased to take
into account the element of surprise and other operational factors
missing from the certification flight test demonstrations.
Operationally, V1 represents the minimum speed from
which the takeoff can be safely continued within the takeoff distance
shown in the AFM, and the maximum speed from which the airplane can be
stopped within the accelerate-stop distance shown in the AFM.
Typically, the pilot not flying the airplane will call out
V1 as the airplane accelerates through this speed. If the
pilot flying the airplane has not taken action to stop the airplane
before this callout is made, the takeoff should be continued unless the
airplane is unsafe to fly.
One commenter states that airplane manufacturers produce
performance data for use by the U.S. military that provides the engine
failure speed, rather than the speed at which the pilot must respond to
the failure. This commenter believes that the military airworthiness
rejected takeoff standards, which provide the crew with the engine
failure speed, are safer than the civil airworthiness standards, which
provide the crew with the V1 speed. The commenter further
notes that many commercial pilots with a military background operate
under the belief that the civil airworthiness standards provide
equivalent safety to the military standards. In the commenter's
opinion, the civil standards provide a lower level of safety, and these
pilots have been given a false sense of security.
The FAA is aware of many differences between the civil and military
takeoff requirements. These differences are indicative of the different
operating needs and environments between civil and military flight
operations. For example, the military standards allow liftoff to occur
at the very end of the runway and obstacles to be cleared with no
safety margin in the event of the failure of the critical engine at the
designated ``go'' speed. In contrast, part 25 requires the airplane to
be at a height of 35 feet at the end of the takeoff distance (on a dry
runway), and obstacles must be cleared by 35 feet plus an additional
safety margin related to the flight path gradient. In summary, the
civil and military airworthiness standards provide for safe operations
within their respective operating environments. It would be
inappropriate, however, to apply unique procedures and techniques from
one operating environment to the other.
One commenter noted that the proposed definition for takeoff
decision speed tends to perpetuate the confusion over the meaning and
use of the V1 speed. The commenter points out that
V1 is really a ``pilot action speed'' that occurs
immediately after the pilot makes the decision to reject the takeoff.
Another commenter suggests that the proposed definition is technically
inaccurate because reducing thrust during a rejected takeoff would not
normally be construed as activating a deceleration device. Hence, the
commenter suggested alternative wording for the words ``the pilot
activates the first deceleration device.''
The FAA agrees with these commenters and has revised the proposal
accordingly. The term ``takeoff decision speed'' has been deleted both
from the proposed definition and from Sec. 25.107(a)(2). The proposal
to define takeoff decision speed in Sec. 1.1 is also withdrawn. The
adopted definition represents a change to the definition of
V1 in Sec. 1.2, rather than an addition to Sec. 1.1. This
revised definition clarifies that V1 represents the minimum
speed from which the takeoff can be safely continued within the takeoff
distance shown in the AFM and the maximum speed from which the airplane
can be stopped within the accelerate-stop distance shown in the AFM. In
addition, the preamble discussion of the proposals has been edited for
additional clarity to present a consistent description of the
V1 concept.
The proposed addition of the definition for VEF to
Sec. 1.2 is adopted as proposed. One commenter misunderstood this
proposal as representing the first time the FAA has sought to define
VEF. For clarification, the term VEF and its
definition were originally added to Sec. 25.107(a)(1) by Amendment 25-
42. The amendment adopted in this rule adds the existing definition for
VEF to the list of abbreviations and symbols in Sec. 1.2.
In addition to the definitions proposed in NPRM 93-8, one commenter
suggests revising the definition of rated takeoff thrust to allow its
use for up to ten minutes of operation. The current definition in
Sec. 1.1 limits the use of takeoff thrust to five minutes or less. The
FAA is currently considering the change proposed by this commenter as
part of a harmonization effort with the European JAA. In the interim,
the FAA has developed a procedure to review and approve specific
requests for the use of takeoff thrust for up to ten minutes duration
on transport category airplanes in the event of an engine failure or
shutdown.
One commenter recommended adding ``wet and dry runway conditions''
to the variables listed in Sec. 25.101(e) for which the airplane
configuration may vary. The rationale the commenter provides for this
recommendation is to encourage optimization of the airplane
configuration. The FAA does not believe that the suggested change will
accomplish the commenter's goal. Section 25.101(e) does not require
applicants to establish an optimum configuration to meet the applicable
requirements. Instead, Sec. 25.101(e) allows applicants to establish
different configurations (e.g., flap settings) to obtain better
performance at different weight, altitude, and temperature conditions.
The same commenter recommends revising Sec. 25.105(a)(2) to require
the takeoff data to be determined in the optimum configuration for the
takeoff conditions specified in Sec. 25.105(c). The commenter believes
that this change would require operators to use the optimum flap
setting for takeoff, rather than allow the use of any flap setting that
meets the applicable regulations. The FAA does not concur with this
recommendations for the following reasons. First, the commenter's
recommendation should be directed at the airplane operating
requirements, rather than the part 25 airworthiness standards. The
effect of the recommended revision to part 25 would be to prohibit
takeoff data from being provided for configurations that were not
deemed to be the optimum configuration. Second, the commenter does not
define how to determine the optimum configuration. The commenter
appears to support using the configuration that would provide the
shortest takeoff and accelerate-stop
[[Page 8306]]
distances. However, this configuration also typically results in the
poorest climb capability after takeoff, and may not be the optimum
configuration from the standpoint of obstacle clearance, noise,
standardization of crew procedures, or fuel use.
The FAA received several comments regarding the proposed change to
Sec. 25.101(i). One commenter recommends deletion of the proposed
requirement to determine the landing distances with worn brakes. This
commenter claims that the effects of worn brakes on landing is
insignificant, and notes that the FAA does not expect this requirement
to reduce the amount of payload that can be carried. The commenter also
notes that there has never been a landing incident or accident in which
a deficiency in brake energy due to wear was a factor, nor is there any
reasonable likelihood that there would ever be one. The commenter goes
on to say that the proposed requirement would result in additional
certification test and flight manual development costs with no
resultant safety benefit to the public.
Although the FAA agrees that the proposed requirement is not likely
to reduce the amount of payload that can be carried for most landings,
the FAA disagrees that the effects of worn brakes on landing will
always be insignificant. The effect of brake wear at the braking energy
levels associated with a landing stop depends on the particular brake
design. To provide for those cases in which the landing distance is
critical, the AFM landing distance data must be based on fully worn
brakes. The proposed requirement only specifies the wear condition of
the brakes for determining the landing distances. No additional AFM
information, and, therefore, no additional flight manual development
costs would be required. The proposed requirement also would not
necessarily result in additional certification testing. The only flight
test that must be performed with worn brakes is the maximum energy
rejected takeoff condition, in which the brakes must be worn to within
10 percent of the fully worn condition. All other data must only meet
the condition that sufficient data be available from airplane flight
tests or wheel-brake dynamometer tests to enable adjustment of all of
the takeoff and landing flight test results to the fully worn level.
For example, the testing performed to determine the effect of worn
brakes on accelerate-stop distances may also be used to determine the
effect of worn brakes on landing distances, if it can be shown to be
applicable.
Another commenter suggests adding the stipulation that the
determination of the accelerate-stop and landing distances must be
based on the demonstrated results obtained by flight test in accordance
with the proposed Sec. 25.735(g). The FAA concurs with the intent of
this suggestion. Instead of modifying the proposed Sec. 25.101(i),
however, the FAA is revising the proposed Sec. 25.735(g) and relocating
it as a new Sec. 25.109(i). The adopted wording clarifies that the
applicant must conduct a flight test demonstration of the maximum brake
kinetic energy accelerate-stop distance with no more than 10 percent of
the allowable wear range remaining on each of the airplane wheel
brakes. This change to the original proposal is also discussed later
relative to the comments received on the proposed Sec. 25.735(g).
A commenter proposes a wording change to Sec. 25.101(i) to
anticipate possible future brake materials that might show an improving
brake performance as the brake wears. This commenter suggests that the
proposed requirement should reference the wear condition that
dynamometer testing indicates as producing the least effective braking
performance. The FAA agrees that the most critical wear condition
should be used to determine the stopping distances and energy capacity
of the brakes. In practice, however, the FAA believes this condition
will always be the fully worn brake. The FAA does not believe that an
extensive dynamometer survey of different wear states is warranted.
One commenter suggests that stopping distances be based on brakes
that are worn to 90 percent of the allowable wear level instead of the
proposed level of fully worn. This commenter states that, in actual
operations, it would be virtually impossible for all the airplane's
brake assemblies to simultaneously be at the fully worn limit of their
allowable wear range. In addition, this commenter believes that such
conservatism in determining the stopping distances to be unwarranted
when combined with the worn brake requirements relating to brake energy
absorption capability. As an alternative, this commenter, joined by a
second commenter, proposes that Sec. 25.101(i) optionally allow
stopping performance to be based on the actual amount of brake wear
existing at the time of each flight. The two commenters state that it
is unnecessary and inappropriate for the regulations to assume the
worst case capability when satisfactory means to determine the actual
capability can be provided. They believe that the proposed regulation
would inhibit the development of technical and procedural advances that
would take into account the actual wear condition of the brakes.
The FAA does not concur with the recommendation to base the
stopping distances on brakes worn to 90 percent of the allowable wear
level. Although operators may typically overhaul brakes before they are
fully worn, and the brakes on different wheels are usually at different
levels of wear, airplanes may legally be operated with all of the brake
assemblies in their fully worn condition. The FAA agrees that it would
be inappropriate for the regulations to assume the worst case
capability when satisfactory means exist to determine the true
capability; however, the operational aspects must also be
satisfactorily addressed.
Regarding the commenters' proposal to allow stopping distances to
be based on the actual brake wear level, the FAA has significant
concerns over the operational aspects. Although it may be possible to
determine the accelerate-stop and landing distances as a function of
brake wear, the FAA considers it unacceptable to use, on a flight-by-
flight basis, the brake wear level as an additional takeoff performance
variable. The added complexity caused by this additional variable would
increase the chances of error in determining the allowable takeoff
weight and the takeoff speeds. Also, the FAA questions whether an
acceptable means can be developed to accurately and reliably determine
the actual wear state of the brake under all operational and
environmental conditions. Finally, extensive certification testing
would be required to determine the stopping distances as a function of
the brake wear level. A linear relationship between these variables
cannot be assumed. Therefore, Sec. 25.101(i) is adopted as proposed,
except for a minor editorial revision for clarification purposes.
Since the certified accelerate-stop and landing distances will
correspond to brakes that are at the fully worn limit of their
allowable wear range, the allowable brake wear range must be specified
as part of the approved type design for the airplane. This information
should be provided on the type certificate data sheet. The allowable
wear range should be defined in terms of a linear dimension in the
axial direction, which is typically determined by measuring the
extension of a pin used to indicate the amount of wear. At the fully
worn limit of the allowable brake wear range, the brake must be removed
from the airplane for overhaul.
Both favorable and adverse comments were received on the FAA's
proposal to
[[Page 8307]]
amend Sec. 25.109 to replace two seconds of acceleration beyond
V1 speed with the distance traversed in two seconds at
V1 speed. The commenters who objected to the proposed
amendments believe the proposal would reduce safety. One commenter who
disagrees with the proposed amendment also states that the comparison
between the one-engine-inoperative and all-engines-operating
accelerate-stop distances, as required by the proposed Sec. 25.109(a),
would become almost meaningless. This commenter claims that ``test
pilot response in the order of milliseconds preempts any significant
difference in acceleration distance between engine out and all engine
acceleration before V1.'' Also, the proposed distance
traversed during two seconds at V1 speed is the same for
both cases, as is the deceleration distance from V1 until
the airplane is stopped.
As discussed previously, the FAA considers the proposed additions
of worn brake and wet runway requirements to significantly improve
takeoff safety. These additional requirements, along with the proposal
to replace the two seconds of acceleration with a distance equal to two
seconds at V1 speed, would provide more rational takeoff
airworthiness standards and an equivalent or higher level of safety
than the current standards. Regarding the comparison of one-engine-
inoperative and all-engines-operating distances, the minimum time
between the critical engine failure speed (VEF) and
V1, as discussed earlier, is one second. During the period
after V1, unless reducing thrust is the first pilot action
following the engine failure, there will be another time interval
before thrust is reduced on the remaining operating engine(s). Since
thrust reversers may not be used in determining the dry runway
accelerate-stop distances, the operating engines (on a turbojet powered
airplane) will continue to produce forward thrust. Therefore (for
turbojet airplanes), the distance to stop from V1 will
usually be longer for all-engines-operating case than for the one-
engine-inoperative case. Whether the sum of the accelerate and stop
distances is greater for the all-engines-operating case as opposed to
the one-engine-inoperative case depends on the time intervals between
VEF and V1, V1 and the pilot action to
reduce thrust, and on the engine transient response (spindown)
characteristics. For wet runways, in which the effect of reverse thrust
would be included, the stopping distance with one-engine-inoperative
will usually be longer than that with all-engines-operating. In
general, the FAA expects the dry runway accelerate-stop distances to be
based on the all-engines-operating case, and the wet runway accelerate-
stop distances to be based on the one-engine-inoperative case.
One commenter suggests that the FAA should provide a statement
proclaiming that the standards proposed in NPRM 93-8 ``reflect the full
intent of the accelerate-stop transition segment AFM distance
construction'' and that ``additional time delays are not envisioned.''
This commenter states that FAA advisory material imposed an additional
two-second time delay beyond that prescribed by Amendment 25-42, and
the commenter desires a clarification that such a situation will not
recur. The FAA intends to revise Advisory Circular (AC) 25-7, ``Flight
Test Guide for Certification of Transport Category Airplanes,'' to be
consistent with this adopted rule and the description of the time
delays provided in this preamble discussion regarding the definition of
V1.
In reviewing the comments, the FAA discovered that the proposed
wording for Sec. 25.109(a) could be interpreted such that speeds
greater than V1 need not be considered in determining the
accelerate-stop distances. However, the airplane will typically exceed
V1 speed during the stop, particularly with all-engines-
operating, even when the pilot applies the brakes at V1. The
proposed amendments to Sec. 25.109(a) have been modified to clarify
that the accelerate-stop distances must include the highest speed
reached during the rejected takeoff maneuver. As modified, these
proposed amendments to Sec. 25.109(a) are adopted.
The FAA received a large number of comments regarding the proposed
method for determining takeoff performance on wet runways. One of the
provisions of the proposed method would allow applicants to use a
simplified approach to determine the braking capability on a wet runway
without the need for specific wet runway flight testing. Based on the
extensive wet runway testing conducted over the past 30 years by the
National Aeronautics and Space Administration (NASA), the FAA, the
aerospace industry, and other organizations around the world (a
compilation of which appears in the docket in ESDU item number 71026),
the FAA proposed using a braking coefficient of one-half the
demonstrated dry braking coefficient. The FAA intended for this one-
half factor to be applied even if the dry runway braking coefficient is
limited by the maximum torque capability of the brake, rather than the
maximum friction capability available from the runway surface.
Several commenters disagree with using a simple one-half factor to
determine the wet runway braking coefficient. One commenter feels the
factor is arbitrary and that using a simple factor is inappropriate.
Another commenter claims that other easily applied methods exist and
should be used to provide a wet runway braking coefficient. This
commenter believes that the proposed method effectively makes the low
speed accelerate-stop data more conservative than the high speed data,
which would be the opposite of what the commenter feels should be done
to increase safety. These commenters did not propose any alternative
methods for determining the wet runway braking coefficient.
Several commenters object to the specific aspect of applying the
one-half factor when the dry runway braking coefficient corresponds to
the maximum torque capability of the brake. In spite of the explanation
provided in the preamble discussion in NPRM 93-8, these commenters
oppose this provision on the basis that the maximum torque capability
of the brake is independent of the runway surface condition. One
commenter conducted laboratory tests of a simulated wet runway to show
that the stopping ability of an airplane on a wet runway is not a
function of the size or torque limit of the brakes. Another commenter
claims that this provision appears to prohibit the effective and safe
use of braking capacity up to the limit of the wet runway braking
coefficient. This commenter points out that an airplane with brakes
that have a low maximum torque capability would be unfairly penalized
relative to an airplane equipped with brakes of a higher maximum torque
capability. Another commenter questions whether the proposed
requirement is a conservative approach resulting from a lack of
appropriate test data.
The FAA agrees that the torque capability of the brake is usually
not a limiting factor on a smooth wet runway. The FAA proposed applying
a factor to the torque limited braking coefficient to represent the
varying relationship between the wet and dry runway braking
coefficients as a function of ground speed. At higher ground speeds,
the wet runway braking coefficient is typically less than one-half the
dry runway braking coefficient. At these higher speeds, the dry runway
braking coefficient is usually limited by the brake's maximum torque
capability. For the typical airplane/brake combination, factoring the
torque limited braking coefficient obtained on a dry runway by one-half
provides a reasonable approximation to the significantly
[[Page 8308]]
reduced braking coefficients observed at high speeds on wet runways.
Because the total stopping distance for a high speed stop is affected
more by the stopping capability at high speeds than at low speeds,
applying the one-half factor only to the non-torque limited braking
coefficient would be inadequate for determining the total distance
needed to stop on a wet runway.
The FAA does not concur with the comment that this proposal would
prohibit the safe and effective use of braking capability on a wet
runway. This proposal only addressed the method for determining the wet
runway accelerate-stop distances presented in the AFM. It would not
affect the manner in which the pilot uses the brakes. The FAA
recognizes, however, that not all airplanes share the same relationship
between V1 speeds and maximum brake torque capability, and
that some airplane types could be affected more than others by this
provision. In recognition of this potential disparity, the proposed
Sec. 25.109(b)(2) would have allowed applicants the option of
demonstrating a higher wet runway braking coefficient.
One commenter suggested that an advisory circular may be necessary
to provide guidance regarding an acceptable method for demonstrating a
wet runway braking coefficient higher than one-half the dry runway
value. Another commenter noted that one flight test, for example,
performed on a damp grooved runway with excellent friction capability
would be an insufficient basis for developing the AFM information
applicable to all wet runways. Another commenter recommended a change
to the FAA proposal to allow the use of methods other than flight
testing to demonstrate a higher wet runway braking coefficient. This
commenter believes that in the near future it may become feasible to
use data obtained from either an analysis, a simulation of the
airplane's braking system, or other sources.
One of the commenters who opposed portions of the FAA proposal
submitted an alternative proposal based on the same ESDU 71026 data
source used to develop the FAA proposal. The commenter proposes an
alternative method to replace the option for demonstrating a braking
coefficient higher than one-half the dry runway braking coefficient.
The following summary represents a brief synopsis of the commenter's
detailed proposal:
a. Derive a standard wet runway braking coefficient versus speed
curve from the ESDU 71026 data. This curve, representing the maximum
braking coefficient available from the runway surface, would be used
for all transport category airplanes as the basis for developing
airplane type specific curves.
b. Apply adjustments to this curve to reflect the capability of an
individual airplane type's anti-skid system on a wet runway. The anti-
skid system capability would be determined either directly from wet
runway testing, or a conservative capability (i.e., somewhat worse than
would be expected if testing were performed) would be assumed, based on
the capability of existing comparable anti-skid systems.
c. Allow higher braking coefficients for suitably maintained
grooved or porous friction course runways.
d. Use the brake torque limitations (i.e., the amount of torque the
brake is capable of producing) that are determined on a dry runway for
both wet and dry runways.
The FAA considers the commenter's proposal to have considerable
merit, not just as a replacement for the demonstration option as the
commenter proposes, but also as a replacement for the one-half the dry
braking coefficient methodology. The commenter's proposal addresses the
shortcomings inherent in the NPRM 93-8 methodology of determining the
wet runway braking coefficient by applying a single adjustment factor
to the dry runway braking coefficient. Under the commenter's proposal,
the wet runway braking capability would more accurately reflect the
significant variation in braking capability with speed that occurs on a
wet runway. Properly reflecting this variation with speed would remove
the need to apply a factor to the dry runway brake torque capability.
As adopted, Sec. 25.109(b) has been revised and new Secs. 25.109
(c) and (d) have been added to prescribe wet runway accelerate-stop
distance standards in a manner consistent with the commenter's
proposal. This final rule is based on the same information as the
original FAA proposal; however, the methodology for determining wet
runway accelerate-stop distances has been changed to more rationally
reflect the various factors affecting wet runway braking. The
methodology adopted by this amendment provides a more accurate
portrayal of wet runway stopping performance than had been proposed in
NPRM 93-8.
Significant issues related to the commenter's proposal, which had
to be addressed prior to preparing this final rule, included:
a. Defining the standard wet runway braking coefficient versus
speed curve, considering the various parameters that affect wet runway
stopping performance.
b. Defining a method for determining the capability of an
airplane's anti-skid system on a wet runway.
c. Establishing conservative levels of anti-skid capability that
could be used in lieu of determining this capability directly from test
data.
d. Determining whether a higher braking capability is appropriate
for use with grooved or porous friction course runways. (This issue is
discussed later along with other comments received on this topic).
ESDU 71026 contains curves of wet runway braking coefficients
versus speed for smooth and treaded tires at varying inflation
pressures. These data are presented for runways of various surface
roughness, including grooved and porous friction course runways.
Included in the data presentation are bands about each of the curves,
which represent variations in: water depths from damp to flooded,
runway surface texture within the defined texture levels, tire
characteristics, and experimental methods. From these data, it is
readily apparent that wet runway stopping performance is significantly
affected by many more variables than dry runway stopping performance.
In order to determine the wet runway stopping distance, a value must be
specified (or assumed) for each of these variables. Since it would be
impractical to try to measure or evaluate each of these variables for
every takeoff, the takeoff data must take into account the conditions
likely to occur in operational service.
It was the FAA's intent with the proposals of NPRM 93-8 to define a
wet runway performance level that would ensure safe operation for the
vast majority of wet runway rejected takeoffs likely to occur. This
same principle was used in specifying values for each of the variables
considered by the adopted wet runway methodology. The resulting
accelerate-stop distances, coupled with information provided to
operators and pilots concerning the use of these data, should greatly
reduce the risk of runway overruns during wet runway operations.
In defining the standard curves of wet runway braking coefficient
versus speed that are prescribed by the equations in Sec. 25.109(c)(1),
the effects of the following variables were considered: Tire pressure,
tire tread depth, runway surface texture, and the depth of the water on
the runway.
Tire Pressure
The effect of tire pressure is taken into account by providing
separate curves (i.e., equations) in Sec. 25.109(c)(1) for
[[Page 8309]]
several tire pressures. As stated in the adopted rule, linear
interpolation may be used for tire pressures other than those listed.
To provide additional safety, Sec. 25.109(c)(1) requires applicants to
base the accelerate-stop distances on the maximum tire pressure
approved for operation. Operating at a tire pressure that is lower than
the maximum tire pressure approved for that airplane will tend to
improve the airplane's stopping capability on a wet runway. Typically,
manufacturer recommended tire pressures are a function of airplane
weight; for operations at less than the maximum approved weight, the
recommended tire pressure would be less than the maximum approved tire
pressure.
Tire Tread Depth
The degree to which water can be channeled out from under the tires
significantly affects wet runway stopping capability. Airplane tires
have ribbed grooves around the circumference of the tire for this
purpose. The texture of the runway surface plays an equally important
role. ESDU 71026 provides braking data for both ribbed and smooth tires
on runways of different surface textures. A method is also provided in
ESDU 71026 for assessing the effects of tire wear. As ribbed tires
wear, the depth of the ribbed grooves decreases, impairing their
ability to channel water out from under the tire.
Surveys conducted by U.S. airplane and tire manufacturers, and
information from major tire retreaders, indicate that the typical
groove depth remaining at the time of tire removal can vary from about
1.5 to 5 mm. Airplane manufacturers' maintenance manuals usually
recommend removal when the tread depth is less than \1/32\ inch (1.2
mm), although operation with zero tread depth is not prohibited. Loss
of tread depth is not the sole criterion for tire removal, however.
Tires with significant tread depth remaining may be removed for other
reasons. Also, it is unlikely that all the tires on a particular
airplane would be worn to the same extent.
The standard curves (i.e., equations) of braking coefficient versus
speed prescribed in Sec. 25.109(c)(1) are based on a tire tread depth
of 2 mm. Since the tread depth of new tires is usually 10-12 mm, 2 mm
represents no more than 20 percent of the original tread depth. FAA
Advisory Circular 121.195(d)-1A, which provides guidance for
determining operational landing distances on wet runways, specifies
that the tires used in flight tests to determine wet runway landing
distances should be worn to a point where no more than 20 percent of
the original tread depth remains. Therefore, the adopted rule, which
reflects industry practice, is also consistent with existing FAA
guidance in this area.
Runway Surface Texture
ESDU 71026 groups runways into five categories. These categories
are labeled ``A'' through ``E,'' with ``A'' being the smoothest and
``C'' the most heavily textured ungrooved runways. Categories ``D'' and
``E'' represent grooved and other open textured surfaces. Category A
represents a very smooth texture (an average texture depth of less than
0.004 inches), and is not very prevalent in runways used by transport
category airplanes. The majority of ungrooved runways fall into the
category C grouping. The curves represented in Sec. 25.109(c)(1), as
adopted, represent a texture midway between categories B and C.
Depth of Water on the Runway
Obviously, the greater the water depth, the greater the degradation
in braking capability. The curves prescribed in Sec. 25.109(c)(1)
represent a well-soaked runway, but with no significant areas of
standing water.
In summary, the curves prescribed in Sec. 25.109(c)(1) represent
the maximum tire-to-ground braking coefficient likely to be available
from a wet runway during a rejected takeoff. They were derived by
interpolating between the curves presented in ESDU 71026 for runway
surface categories B and C, adjusted to represent tires with 2 mm tread
depth remaining, and extrapolated to cover the range of V1
speeds to be expected. The resulting curves were then smoothed and
reduced to a mathematical form for inclusion in the rule. The
capability for a particular airplane type to achieve this braking
coefficient depends on: (1) The amount of torque its brakes are capable
of producing, and (2) the performance of its anti-skid system. How the
revised regulation addresses these two components is discussed in the
ensuring paragraphs.
The torque capability of the brakes is evaluated during the flight
testing that applicants conduct to determine the dry runway accelerate-
stop distance. Since the torque capability is independent of the runway
surface condition, the torque capability demonstrated by the dry runway
flight tests also represents the maximum torque available during a wet
runway stop. As adopted, Sec. 25.109(b)(2)(i) limits the stopping force
from the wheel brakes used to determine the wet runway accelerate-stop
distance to the stopping force determined in meeting the requirements
of Sec. 25.101(i) (worn brakes) and Sec. 25.109(a) (the dry runway
accelerate-stop distance). This provision prohibits applicants from
using a brake torque that exceeds the dry runway torque limits when
determining the wet runway accelerate-stop distance.
An airplane's anti-skid system varies the braking action to prevent
locked wheel skids and to maximize stopping performance to the extent
possible. How close the anti-skid system comes to obtaining the maximum
braking friction available between the tires and the runway is referred
to as the anti-skid system efficiency.
As adopted, Sec. 25.109(c)(2) requires applicants to adjust the
maximum tire-to-ground wet runway braking coefficient determined in
Sec. 25.109(c)(1) for the efficiency of the anti-skid system.
Applicants will have the option of either determining the anti-skid
system efficiency directly from flight tests on a wet runway, or using
one of the anti-skid efficiency values specified in Sec. 25.109(c)(2).
Regardless of which method is used, an appropriate level of flight
testing must be performed to verify that the anti-skid system operates
in a manner consistent with the efficiency value used, and that the
system has been properly tuned for operation on wet runways.
For applicants using the anti-skid efficiency values specified in
Sec. 25.109(c)(2), a minimum of one complete wet runway stop, or
equivalent segmented stops, should be conducted at an appropriate speed
and energy to cover the critical operating mode of the anti-skid
system. This testing can be performed as part of the anti-skid
compatibility testing on a wet runway that is already required for
brake and anti-skid system approval under Sec. 25.735. Therefore, for
applicants using the anti-skid efficiency values specified in
Sec. 25.109(c)(2), no additional flight tests need actually be
performed. Existing flight test may need to be modified somewhat to
ensure that appropriate data are obtained to verify that the anti-skid
system operates in a manner consistent with the efficiency value used,
and that the system has been properly tuned for operation on wet
runways.
As revised, Sec. 25.109(c)(2) identifies three different classes of
anti-skid systems, and specifies a unique efficiency value associated
with each one. This classification of anti-skid system types and the
assigned efficiency values are based on information contained in
Society of Automotive Engineers (SAE) Aerospace Information Report
(AIR) 1739, title ``Information on
[[Page 8310]]
Anti-Skid Systems.'' The efficiency values prescribed in
Sec. 25.109(c)(2) represent the worst system performance expected for
each type of system after being properly tuned for operation on wet
runways. The SAE document is available in the public docket for this
rulemaking.
The three classes of anti-skid systems represent evolving levels of
technology and differing performance capabilities on dry and wet
runways. On/off systems are the simplest of the three types of anti-
skid systems. For these systems, full metered brake pressure (as
commanded by the pilot) is applied until wheel locking is sensed. Brake
pressure is then released to allow the wheel to spin back up. When the
system senses that the wheel is accelerating back to synchronous speed
(i.e., ground speed), full metered pressure is again applied. The cycle
of full pressure application/complete pressure release is repeated
throughout the stop (or until the wheel ceases to skid with pressure
applied).
Quasi-modulating systems, the second type of anti-skid system,
attempt to continuously regulate brake pressure as a function of wheel
speed. Typically, brake pressure is released when the wheel
deceleration rate exceeds a preselected value. Brake pressure is re-
applied at a lower level after a length of time appropriate to the
depth of the skid. Brake pressure is then gradually increased until
another incipient skid condition is sensed. In general, the corrective
actions taken by these systems to exit the skid condition are based on
a pre-programmed sequence rather than the wheel speed time history.
Fully modulating systems, the third type of anti-skid system, are a
further refinement of the quasi-modulating systems. The major
difference between these two types of anti-skid systems is in the
implementation of the skid control logic. During a skid, corrective
action is based on the sensed wheel speed signal, rather than a pre-
programmed response. Specifically, the amount of pressure reduction or
reapplication is based on the rate at which the wheel is going into or
recovering from a skid. Also, higher fidelity transducers and upgraded
control systems are used, which respond more quickly.
For applicants who elect to determine the anti-skid efficiency
directly from flight tests, sufficient flight testing, with adequate
instrumentation, must be conducted to ensure confidence in the
efficiency obtained. Although additional flight testing will be
necessary, the FAA does not expect applicants to use this method for
determining the anti-skid efficiency unless proportionate benefits
(i.e., an increase in takeoff weight) are obtained. A minimum of three
complete stops, or equivalent segmented stops, should be conducted on a
wet runway at appropriate speeds and energies to cover the critical
operating modes of the anti-skid system.
As adopted, Sec. 25.109(b)(2)(ii) also requires applicants to
adjust the wheel brakes stopping force to take into account the effect
of the distribution of the normal load between braked and unbraked
wheels at the most adverse center-of-gravity position approved for
takeoff. The stopping force due to braking is equal to the braking
coefficient multiplied by the normal load (i.e., the effective weight)
on the braked wheels. The location of the airplane's center-of-gravity,
which is a function of the airplane's configuration and how it is
loaded (i.e., the position of passengers, baggage, cargo, etc.),
affects how the load is distributed between braked and unbraked wheels.
Typically, the nose wheels of transport category airplanes are
unbraked, although some airplanes also have some of the main gear
wheels unbraked). This effect must be taken into account for the most
adverse center-of-gravity position approved for takeoff. The most
adverse center-of-gravity position is that which results in the least
load on the braked wheels.
For the following reasons, the FAA regards the wet runway
methodology issued in this final rule to be a logical outgrowth of the
proposal published in NPRM 93-8. First, the final rule methodology
relies on the same technical basis as the original proposal. Second, it
responds to a comment raised during the NPRM 93-8 public comment
process. And third, it is consistent with the overall intent of this
rulemaking, which is to more rationally address relevant operational
factors rather than applying more restrictive standards to all
operating conditions. This methodology also provides applicants with
the ability to better control any increased costs resulting from the
addition of wet runway accelerate-stop requirements to part 25, while
ensuring safer wet runway operations. Depending on the desired balance
between manufacturing costs (including design and flight testing) and
operational capabilities, an applicant can make informed choices
regarding design characteristics (e.g., type of anti-skid system,
takeoff speeds) and the level of wet runway testing to perform (i.e.,
use of the anti-skid efficiency values provided in the rule versus
determining the efficiency directly from flight tests).
The FAA recognizes that extensive guidance material will be
necessary to assist applicants in complying with the wet runway
accelerate-stop distance requirements incorporated in this amendment.
Published elsewhere in this issue of the Federal Register is a notice
of availability for a proposed revision to AC 25-7, ``Flight Test Guide
for Certification of Transport Category Airplanes.'' A request for
comments is included in that notice of availability. The proposed
revision includes detailed guidance for:
a. Using reverse thrust in determining wet runway accelerate-stop
distances;
b. classifying the types of anti-skid systems;
c. Verifying the type of anti-skid system installed on the airplane
and that it is properly tuned for operation on wet and slippery
runways;
d. Determining the anti-skid efficiency value; and
e. Developing an analytical model of wet runway braking performance
in accordance with Sec. 25.109(c).
One commenter points out that many operators already use a form of
wet runway takeoff performance data, which is provided to them by the
airplane manufacturers as unapproved guidance information. These data,
used on a voluntary basis to provide additional safety on wet runways,
are typically developed using criteria similar to those proposed in
NPRM 93-8. Another commenter believes that the proposed wording for
Secs. 91.605(b)(3), 121.189(e), and 135.379(e) would result in
retroactive changes to those airplanes for which the AFMs contain wet
runway information carried over from previous foreign certifications.
(Some foreign certification authorities, notably the United Kingdom
Civil Aviation Authority, have required wet runway performance
information to be included in the AFM.) This commenter notes that use
of such data has not been required in the past in U.S. operations and
does not necessarily reflect the standards proposed in NPRM 93-8.
Although the commenter supports the proposal in general, it is
suggested that the wording be changed to specify that the wet runway
requirements apply only to airplanes certificated after the proposed
amendment becomes effective.
The FAA acknowledges that airplane manufacturers have for many
years produced guidance information, including takeoff performance
data, for wet runway operations. In general, the FAA supports the
voluntary use of these available data to provide additional safety on
wet runways for existing transport category airplanes, as long as
compliance with the applicable
[[Page 8311]]
airworthiness and operating rules is maintained.
The FAA did not intend, by the proposed wording Secs. 91.605(b)(3),
121.189(e), and 135.379(e), to effectively apply the proposed wet
runway standards retroactively. Operators should be aware that the
approved portion of the AFM (containing the operating limitations) for
a U.S. operator should only reflect the FAR and should not contain
extraneous information carried over from a foreign certification. Such
information may, however, appear in an unapproved portion of the AFM as
supplementary guidance information. Operators may use this information
(as long as it does not conflict with the FAR), but are not required to
abide by it.
The FAA does not agree with the comment to limit application of the
proposed operating rules only to those airplanes certificated after
this amendment becomes effective. Some manufacturers have elected to
comply with the standards proposed in NPRM 93-8 prior to the adoption
of this final rule. The AFMs for the affected airplane types contain
takeoff and accelerate-stop distance limitations for takeoffs on wet
runways, and operators must comply with these limitations, regardless
of the date the airplane was certificated. Therefore, these amendments
to Secs. 91.605(b)(3), 121.189(e), and 135.379(e) are adopted
essentially as proposed, but with a clarification that this provision
applies to operating limitations, if they exist, associated with the
minimum distances required for takeoff from wet runways. As discussed
earlier, further consideration of retroactive application of the
requirements adopted by this final rule will be added to the FAA/JAA
harmonization work program.
Several commenters recommend that the proposed standards be revised
to allow a higher wet runway braking coefficient to be used for grooved
runways or runways treated with a porous friction course (PFC) overlay,
without the need for additional flight testing. These commenters point
out that runway friction measurement tests show that a wet runway with
grooves or a PFC surface overlay has much better friction
characteristics than a smooth surface. According to these commenters,
providing credit for the improved stopping capability on these surfaces
will result in significant public safety benefits by helping to
expedite future runway improvements and by providing a strong incentive
to properly maintain these surfaces. The commenters believe it is
neither necessary nor in the public interest to avoid or defer this
issue, considering the significant effort that has already been made by
airport operators, both domestic and foreign, to improve runway
surfaces.
To facilitate timely action on this issue, these commenters propose
that the FAA initially adopt a value that the commenters consider to be
very conservative (i.e., a much lower wet runway braking coefficient
than would be expected). Most of these commenters propose using a wet
runway braking coefficient for grooved and PFC runways equal to 70
percent of the dry runway braking coefficient, although one commenter
proposed a factor of 80 percent. For comparison purposes, one commenter
reports that tests conducted using a Boeing 737-300 airplane showed wet
grooved runway braking capability that was equal to, or in some cases
greater than, 95 percent of that obtained on a dry runway. The
commenters note that a longer term rulemaking activity could be
undertaken in the future to establish a higher factor, if warranted.
One of these commenters provided information relative to grooved
and PFC runway credit in Japan. This commenter states that the Japanese
Civil Aviation Bureau allows a wet runway braking coefficient of 70 to
80 percent of the dry runway value to be used for grooved or PFC
runways. In Japan, Most of the runways at civil airports are grooved,
and periodic friction surveys are conducted to assure that the surfaces
are properly maintained. These surveys are done by using a combination
of visual inspections and friction measuring devices.
The FAA agrees that grooved and PFC runways can offer substantial
safety benefits in wet conditions. The FAA has taken an active role
since the late 1960's in evaluating the benefits of these runway
surface treatments and supports their use throughout the U.S. Tests
conducted by the FAA, NASA, and others confirm that applying a factor
of 70 percent to the dry runway braking coefficient, as proposed by the
commenters, would conservatively represent the stopping performance on
properly designed, constructed, and maintained grooved and PFC runways.
A summary of these test data has been placed in the docket. The actual
friction capability of grooved and PFC runways varies, however,
depending on variables such as groove shape, depth, and spacing, method
used to construct the grooves, type of pavement surface, volume and
type of airplane traffic, frequency of pavement evaluations, and
maintenance. The FAR currently do not contain mandatory standards
regarding the design, construction, and maintenance of grooved or PFC
runways, but AC 150/5320-12B, ``Measurement, Construction, and
Maintenance of Skid-Resistant Airport Pavement Surfaces,'' provides
relevant guidelines and procedures.
The FAA concurs with the commenters' proposal and agrees that it
presents an opportunity to provide an additional incentive for airport
operators to install and maintain grooved and PFC runways. The FAA
agrees that 70 percent of the dry runway braking coefficient
conservatively represents the stopping performance on properly
designed, constructed, and maintained grooved or PFC runways. Using a
simple factor applied to the dry runway braking coefficient is
appropriate for grooved and PFC runways because the braking
coefficient's variation with speed is much lower on these types of
runways.
As noted in the earlier discussion of the parameters affecting wet
runway stopping performance, ESDU 71026 contains data corresponding to
grooved and PFC surfaces. An evaluation of the ESDU data reveals that
using a surface texture mid-way between surfaces D and E in combination
with typical anti-skid efficiencies provides approximately the same
airplane stopping performance as using 70 percent of the dry runway
braking capability.
In response to the comments regarding grooved and PFC runways, a
new Sec. 25.109(d) is adopted to establish an optional wet runway
braking coefficient for grooved or PFC runways. The braking coefficient
for determining the accelerate-stop distance on grooved and PFC runways
is defined in Sec. 25.109(d) as either 70 percent of the value used to
determine the dry runway accelerate-stop distances, or a value based on
the ESDU data and derived in a manner consistent with that used for
ungrooved runways. Section 25.105(c)(1) is revised to allow applicants,
at their option, to provide data for grooved and PFC runways, in
addition to the smooth surface runway data that is currently required.
In addition, the existing Sec. 25.109(d) is revised to remove the words
``smooth'' and ``hard-surfaced'' and redesignated as Sec. 25.109(h).
Section 25.1533(a)(3) is amended to allow wet runway takeoff
distances on grooved and PFC runways to be established as additional
operating limitations, but approval to use these distances is limited
to runways that have been designed, constructed, and maintained in a
manner acceptable to the FAA Administrator. In conjunction,
Secs. 91.605(b)(3), 121.189(e), and 135.379(e) of the operating rules
are
[[Page 8312]]
amended to limit the use of the grooved and PFC wet runway accelerate-
stop distances to runways that the operator has determined have been
designed, constructed, and maintained in a manner acceptable to the FAA
Administrator. The page(s) in the AFM containing the wet runway
accelerate-stop distances for grooved and PFC runways should contain a
note equivalent to the following: ``These accelerate-stop distances
apply only to runways that are grooved or treated with a porous
friction course (PFC) overlay that the operator has determined have
been designed, constructed, and maintained in a manner acceptable to
the FAA Administrator.''
Airplane operators who wish to use the grooved or PFC runway
accelerate-stop distances must determine that the design, construction,
and maintenance aspects are acceptable for each runway for which such
credit is sought. In making these determinations, operators may rely on
certifications from airport operators or independent evaluations of
runways. In either case, it is expected that operators will be able to
demonstrate that their determinations are well founded. Acceptable
runways should be listed in Part C of the operator's approved
operations specifications (for those operators required to have
operations specifications).
FAA AC 150/5320-12B provides guidance regarding grooved and PFC
runway construction and maintenance techniques that are considered
acceptable to the Administrator. These criteria for obtaining
operational approval to use the grooved and PFC wet runway accelerate-
stop distances are consistent with the guidance provided in AC
121.195(d)-1A for approval to use operational landing distance for wet
runways. After adoption of this final rule, the FAA also intends to
include this information in an update to AC 91-6A, ``Water, Slush, and
Snow on the Runway.''
Under the proposals for Secs. 25.109 (c) and (d) in NPRM 93-8, wet
runway accelerate-stop distances may include the additional stopping
force provided by reverse thrust; however, including this stopping
force would be prohibited when determining the dry runway accelerate-
stop distances. Most of the commenters supported the proposal for wet
runways, although several commenters noted that several important
aspects were not addressed. These aspects include issues such as
reliability of the trust reversers, piloting procedures,
controllability in crosswinds, flight test methods, etc.
The FAA agrees that detailed guidance material is needed, relative
to thrust reversers, to define an acceptable means to comply with the
proposed requirements of Sec. 25.109(c). As mentioned earlier, the FAA
intends to propose specific guidance material soon as part of a
revision to AC 25-7. In general, the FAA intends to propose that: (1)
Acceptable procedures should be developed and demonstrated, including
the time needed to accomplish these procedures; (2) the responses and
interactions of airplane systems should be taken into account; (3) the
recommended level of reverse thrust should be easily obtainable under
in-service conditions (e.g., by providing a detent or other tactile
method of thrust selection); (4) directional control should be
demonstrated with maximum braking on a wet runway with a ten-knot
crosswind from the most adverse direction; (5) the probability of
failure should be no more than 1 per 1000 selections; (6) inoperative
thrust reversers at dispatch should be taken into account; (7)
satisfactory engine operating characteristics should be demonstrated;
and (8) appropriate flight tests should be conducted to determine the
effective stopping force provided by reverse thrust, and to validate
the total stopping force provided by all of the decelerating means.
One commenter proposed an amendment to the existing Sec. 25.109(c)
to clarify that a finding of ``safe and reliable'' for any deceleration
means other than wheel brakes must take into account the interactions
and interdependencies of the various systems involved, and that
consistent results must be expected under all conditions covered by the
AFM. This comment is directed primarily at a landing situation in which
slippery runways and higher than normal approach speeds could thwart or
delay sensing logic for determining whether the airplane is on the
ground. Consequently, the operation of any deceleration means that can
only be activated on the ground (e.g., ground spoilers and thrust
reversers) would also be delayed.
Under the existing Secs. 25.109(c) and 25.1309, the FAA already
reviews the system operation and inter-compatibility issues that would
be addressed by the commenter's proposed changes to Sec. 25.109(c).
Therefore, the FAA considers these proposed changes to be unnecessary.
One commenter noted that the same reasons in the FAA's proposal for
denying accelerate-stop distance credit for the use of reverse thrust
on dry runways also apply to wet runways. Therefore, if dry runway
accelerate-stop distances need the safety margin provided by not
including the effects of reverse thrust, then so do the wet runway
accelerate-stop distances. The FAA does not concur. As stated in the
discussion of the proposal, the FAA believes that the additional safety
provided by not accounting for reverse thrust in calculating the
accelerate-stop distance on a dry runway is necessary to offset other
variables that can significantly affect the dry runway accelerate-stop
performance. Examples of variables that can significantly affect the
dry runway accelerate-stop performance include: runway surfaces that
provide poorer friction characteristics than the runway used during
flight tests to determine stopping performance, dragging brakes, brakes
whose stopping capability is reduced because of heat retained from
previous braking efforts, etc. Although these variables may also be
present for wet runways, their effects are adequately covered by the
adopted method of determining the stopping capability on a wet runway.
This method provides a margin of safety by using conservative
assumptions regarding runway surface texture, tire tread depth, tire
inflation pressure, anti-skid efficiency, etc.
Despite the reasons the FAA presented in NPRM 93-8 for denying
accelerate-stop distance credit for the use of reverse thrust on dry
runways, several commenters propose that reverse thrust credit be
permitted, at least to the extent that it offsets any performance
degradation due to worn brakes. These commenters claim that the
majority of the factors degrading accelerate-stop performance have been
taken into account; therefore, it would be appropriate to include the
positive effect of reverse thrust. These commenters also note that
reverse thrust capability is provided on nearly all commercial jet
transport airplanes, current thrust reversers are reliable, flightcrews
are trained to use reverse thrust, and its use is a normal part of
operational stopping procedures. Also, the probability of a thrust
reverser failing to operate, combined with the probability of all
brakes being at the fully worn limit, is very low, and there would be
an even lower probability of these factors occurring in combination
with a takeoff rejected from a critically high speed. Under the
proposal offered by most of these commenters, the dry runway
accelerate-stop distance would be required to be the greater of either:
(1) The distance determined using new brakes without reverse thrust, or
(2) the distance determined using worn brakes
[[Page 8313]]
with reverse thrust. Since item (1) corresponds to the current
standards, this proposal would not reduce the accelerate-stop distance
to less than what is currently required. The effect of the commenters'
proposal would be to offset any loss in stopping capability associated
with worn brakes.
As stated previously, the FAA considers that the additional safety
provided by not including the effect of reverse thrust for the
accelerate-stop distance on a dry runway is necessary to offset other
variables that can significantly affect the dry runway accelerate-stop
performance. The effect of these other variables on the dry runway
accelerate-stop distance are unchanged by this rulemaking. Although the
part 25 airworthiness standards are being made more stringent by adding
requirements related to worn brakes and wet runways, the overall effect
of these additions are partially offset by the change in the method
used to account for the time it takes the pilot to perform the
procedures for rejecting the takeoff. Further alleviating provisions
are inappropriate because they would unacceptably reduce the level of
safety. Therefore, Secs. 25.109(c) and (d) are amended as proposed in
NPRM 93-8, except that they have been re-designated as paragraphs (e)
and (f), respectively.
As part of the proposed wet runway standards, Secs. 25.13 (a) and
(b) would allow the airplane's height over the end of the runway (known
as the screen height) to be reduced from 35 feet on dry runways to 15
feet on wet runways. Some commenters object to reducing the screen
height for wet runways, stating that safety margins would be reduced
for takeoffs that are continued following an engine failure. One
commenter would accept a reduced screen height only if operators are
first required to use the configuration that provides the best short
field performance. The FAA response to the latter comment was provided
in the discussion of the commenter's proposed change to
Sec. 25.105(a)(2).
The FAA proposed reducing the required screen height for wet
runways to re-balance the available safety margins, in a manner that
does not impose significant costs on airplane operators, when taking
off from a wet runway. On a wet runway, the distance needed to stop the
airplane increases significantly due to the reduced braking
effectiveness. On the other hand, the distance needed to complete a
continued takeoff is generally unchanged from that needed for a dry
runway. By reducing the required screen height on a wet runway, a lower
V1 speed can be used. The effect of lower V1
speeds will be to reduce the number of rejected takeoffs that occur on
wet runways, and to reduce the speed from which these takeoffs are
rejected. The latter effect is considered especially important because
the braking capability on a wet runway is significantly poorer at
higher speeds.
As noted by one of the commenters, any reduction in the number of
takeoffs that are rejected will produce an equal number of additional
continued takeoffs. Because of the lower V1 speed, the
airplane's height over the end of the runway for these takeoffs, as
well as the ensuring flight path, will be lower than would normally be
achieved on a dry runway. If a clearway area is available, however, the
minimum height of the airplane over the end of a dry runway may, under
the current standards, be as low as 13 to 17 feet. On this basis, the
FAA considers a minimum screen height of 15 feet to be acceptable when
the runway is wet.
Allowing the screen height to be reduced on wet runways also
reduces the cost burden imposed on airplane operators by the wet runway
standards. By taking into account the degraded braking capability on
wet runways, these standards may reduce the maximum weight at which the
airplane would be allowed to take off from a given runway. If a screen
height of 35 feet were retained for wet runways, an even greater
reduction in takeoff weight capability could be necessary.
In the proposed Sec. 25.113(c), the FAA intended to require that
the minimum screen height on a wet runway with a clearway would not be
lower than either: (1) 15 feet, or (2) the screen height that could be
achieved if the runway were dry. A clearway is an area at least 500
feet wide beyond the departure end of the runway that has not obstacles
protruding above a 1.25 percent upward sloping gradient. On a dry
runway, up to one-half of the distance traversed between liftoff and a
height of 35 feet may be over the clearway. As noted earlier, the
screen height (i.e., the height at the end of the runway) achieved on a
dry runway with clearway may end up being as low as 13 feet.
Accordingly, a higher takeoff weight is possible when a clearway is
present. The words ``but not beyond the end of the runway'' included in
the proposal for Sec. 25.113(b)(2) would effectively require the wet
runway screen height to be not less than 15 feet. Under the proposed
wording, therefore, the presence of clearway could not be used to
increase the takeoff weight on a wet runway. Also, in some instances,
the minimum screen height on a wet runway would be higher than that for
a dry runway.
Several commenters expressed confusion over the discrepancy between
the FAA's intent, as expressed in the preamble to NPRM 93-8, and the
proposed wording for Secs. 25.113(b) (2) and (c). One commenter noted
that the words ``but not beyond the end of the runway'' appear to
inappropriately introduce an operating rule into the type design
standards. This commenter also notes that the quoted phrase does not
appear in the JAA's equivalent NPA. This commenter further suggests
that removing the quoted phrase would accomplish the FAA's stated
intent of allowing a very limited takeoff weight increase on wet
runways when clearway is present.
Another commenter recommends that maximum clearway credit be
permitted in combination with the 15-foot screen height on a wet
runway. The commenter notes that V1 speed could then be
reduced even further, thus providing additional safety in the event of
a rejected takeoff on a wet runway. The FAA infers that this commenter
is proposing that half of the distance traversed between liftoff and a
height of 15 feet be permitted to occur over the clearway. Because of
the parabolic shape of the flight path, the airplane may end up being
only five to eight feet high at the end of the runway. The point at
which the airplane lifts off would thus be very near the end of the
runway. As discussed in NPRM 93-8, the FAA considers such a situation
to be unacceptable. The possibility of standing water on the wet
runway, or operational considerations such as a late or slow rotation
to the liftoff attitude, emphasize the need to require liftoff to occur
well before the end of the runway.
Other commenters, including an international association
representing airplane operators, suggest that the potential benefit
provided by the FAA's intended proposal regarding clearway on a wet
runway is so small that it is insignificant. These commenters are
willing to accept the slight conservatism associated with prohibiting
credit for clearway in conjunction with the 15-foot screen height on
wet runways in favor of simplifying and clarifying the rule language.
The FAA concurs with this comment and is amending Sec. 25.113
accordingly. The phrase ``but not beyond the end of the runway,''
contained in the proposed Sec. 25.113(b)(2), is removed. The proposed
Sec. 25.113(c) is clarified to prohibit a screen height of less than 15
feet on a wet runway. If the limiting takeoff distance is determined by
the all-engines-operating condition, where
[[Page 8314]]
the minimum height at the end of the takeoff distance remains 35 feet,
clearway credit is allowed on a wet runway in the same manner as it is
allowed on a dry runway. Also, Sec. 25.113 is amended to add the
provision that in the absence of clearway, the takeoff run is equal to
the takeoff distance. This provision is added only to ensure
completeness of the definition of takeoff run within the airworthiness
standards and is in accordance with standard industry practice. The
current requirement does not define the takeoff run when clearway is
not present.
Some commenters apparently misunderstand some aspects of the wet
runway standards, especially the effect of Secs. 25.109(b)(1) and
25.113(b)(1). These sections require the accelerate-stop and takeoff
distances on a wet runway (at the wet runway V1 speed) to be
at least as long as the corresponding distances on a dry runway (at the
dry runway V1 speed). These requirements therefore ensure
that the maximum takeoff weight for a wet runway can never be higher
than that allowed when the runway is dry. In practice, applicants
should use the following procedure to determine takeoff performance
when the runway is wet. First, conduct the takeoff performance analysis
assuming the runway is dry. Then, repeat the analysis using wet runway
data, including the wet runway V1 speed. The lowest takeoff
weight from these analyses is the maximum takeoff weight that can be
used when the runway is wet. For this takeoff weight, determine and
compare the accelerate-stop and takeoff distances applicable to both
dry and wet conditions. The longer of each of these accelerate-stop and
takeoff distances apply when the runway is wet.
The FAA received only one comment related to the proposed change to
Sec. 25.115(a). This proposed change would allow the airplane's height
over any obstacles to be reduced by an amount corresponding to the
reduced screen height allowed when taking off from a wet runway. The
commenter suggested that the current obstacle clearance criteria should
be updated to represent more realistic operational conditions. The
commenter is referring to the criteria used to evaluate whether the
obstacle must be cleared vertically, or whether an operator can
consider the obstacle to be laterally outside of the airplane's path.
The FAA is currently developing an advisory circular that will address
this issue in detail. Therefore, Sec. 25.115(a) is amended as proposed.
The FAA received several comments on the proposed changes to
Sec. 25.735. One commenter proposed that Sec. 25.735(f) refer to the
wear condition that provides the least effective braking performance.
This comment is related to a similar comment regarding Sec. 25.101(i).
As discussed in response to the earlier comment, the FAA believes that
the fully worn condition will always provide the least effective
braking performance.
This commenter also suggests that the flight test proposed under
Sec. 25.735(g) is unnecessary. The commenter proposes that a flight
test should be required only if poor correlation exists between
dynamometer test results and flight test results. The commenter also
believes that a rejected takeoff may not represent the most severe
stopping condition. For example, landing at the maximum landing weight
with the flaps retracted may involve higher stopping energies. For this
reason, the commenter suggests that Sec. 25.735(g) refer to the most
severe stop rather than a rejected takeoff.
The flight test proposed in Sec. 25.735(g) is the only flight test
that would be required to be conducted at a specific brake wear level.
The FAA considers this test to be a necessary demonstration of the
airplane's ability to safely stop under the most critical rejected
takeoff condition. For the remainder of the flight testing to determine
the rejected takeoff and landing stopping distances, the brakes may be
at any wear level desired by the applicant (including new brakes).
Dynamometer testing could be used to determine the difference in
stopping capability between fully worn brakes and the brake wear level
used in the flight tests. This difference would be applied to the
flight test results to determine the stopping distances for fully worn
brakes.
For the purposes of this demonstration, the FAA considers the
maximum kinetic energy rejected takeoff to be the most critical
stopping condition. Therefore, the FAA does not concur with the
commenter's suggestion to replace the reference to rejected takeoff in
the flight test demonstration with a reference to the most severe stop.
However, from a brake approval standpoint, the FAA agrees that the
brakes, in the fully worn condition, should be capable of absorbing the
energy produced during the most severe stopping condition. The FAA has
tasked a harmonization working group with recommending new or revised
requirements for approval of brakes installed on transport category
airplanes, and this working group is expected to recommend proposed
standards addressing this issue.
Another commenter suggests that the flight test demonstration
referenced by the proposed Sec. 25.735(g) should include a two-second
overshoot of V1, before applying the brakes, to allow for
the average pilot response time. The FAA does not concur with this
comment because V1 represents the highest speed at which the
pilot should take the first action to reject the takeoff. Also, the
procedures used during the flight test demonstration, including the
time at which the pilot applies the brakes, should be consistent with
the rejected takeoff procedures provided by the applicant in the AFM.
One commenter proposed that Sec. 25.735(f) be clarified to allow
for other devices inherent in a particular airplane design that may be
used to dissipate energy. Failure to allow such credit, claims the
commenter, will diminish the value of technological improvements in
energy dissipation devices that are likely to be introduced to improve
airplane stopping performance under wet runway conditions.
The current Sec. 25.735(f) allows for the use of the same
decelerating means to determine the brake kinetic energy capacity
rating as are used to determine the dry runway accelerate-stop
distances. The energy absorption capability of the brake is generally
more of a concern on a dry runway than on a wet runway because of the
difference in deceleration capability. To receive credit for energy
dissipation devices that are likely to be introduced to improve
airplane stopping performance under wet runway conditions, these
devices must also provide proportionate benefits when the runway is
dry, as well as meet the safety and reliability criteria of the amended
Sec. 25.109(e). Within these constraints, the FAA will consider any
technological improvements in energy deceleration devices at the time
such devices are proposed for evaluation.
Two commenters suggest that the proposed amendment to associate the
brake energy rating of Sec. 25.735(f) with brakes in the fully worn
condition is inappropriate and could lead to confusion during the brake
approval process. These commenters concur with the intent that each
wheel-brake assembly, when fully worn, be capable of absorbing the
maximum kinetic energy for which it is approved. However, these
commenters note that the kinetic energy level defined in Sec. 25.735(f)
is the same energy level used in Technical Standard Order (TSO)-C26c
for demonstrating the capability of the brake to successfully complete
100 landing stops with no refurbishment or other changes made to brake
system components (except for one change in
[[Page 8315]]
brake lining material). (TSO-C26c contains minimum performance
standards for aircraft landing wheels and wheel-brake assemblies and
specifies the brake dynamometer tests to demonstrate compliance with
these standard.) Because of the relationship between Sec. 25.735(f) and
the TSO, any change to the definition of the energy level in
Sec. 25.735(f) would presumably also apply to the TSO. Since the TSO
100-stop test is intended to verify that the brake has acceptable
structural durability, rather than to demonstrate the capability to
successfully complete a high energy stop in the fully worn condition,
the combination of the worn condition with the TSO energy level would
be inappropriate. A brake that is fully worn at the beginning of the
100-stop test would be unable to successfully complete the test.
One of the commenters notes that the TSO also requires a test
involving one stop at the maximum rejected takeoff kinetic energy.
According to the commenter, it is this test that should be conducted
with a fully worn brake. The energy rating demonstrated by this test is
not explicitly referenced in part 25, but is contained in JAR-25 as JAR
25.735(h). The commenter proposes adding JAR 25.735(h) to part 25 to
harmonize the two standards and to help clarify the application of the
worn brake requirements. This commenter also suggests adding references
to the applicable TSO and clarifying that the formula provided in
Sec. 25.735(f)(2) need only be modified in cases of designed unequal
braking distributions. Uneven braking distributions can unintentionally
occur during flight tests, but this characteristic cannot be predicted
during the design or qualification stages for which Sec. 25.735(f)(2)
is relevant.
The FAA concurs with these proposals. As amended, Sec. 25.735(f)
defines the landing kinetic energy rating to be used during
qualification testing per the applicable TSO or other qualification
testing used to show an equivalent level of safety, as necessary to
obtain the approval required by Sec. 25.735(a). The proposed reference
to a fully worn brake is inappropriate in this section and has been
removed. In the proposed revision to AC 25-7, for which the notice of
availability is published elsewhere in this issue of the Federal
Register, the FAA proposes to clarify that the relevant TSO 100-stop
test may begin with a brake in any condition representative of service
use, including new. In addition, a new Sec. 25.735(h), based on JAR
25.735(h), has been added. This section is similar to Sec. 25.735(f),
but defines the rejected takeoff, rather than the landing kinetic
energy rating used in the applicable TSO. Unlike the landing brake
kinetic energy rating, the rejected takeoff brake kinetic energy rating
must be demonstrated with a fully worn brake. Finally, both the revised
Sec. 25.735(f)(2) and the new Sec. 25.735(h)(2) require the referenced
formulae for determining the brake energy capacity rating to be
modified only in the case of designed unequal braking distributions.
The format of the existing Sec. 25.735(f)(2), with respect to this
provision, has been adjusted to conform to Federal Register formatting
guidelines, and the new Sec. 25.735(h)(2) has been formatted similarly.
With these changes, the final rule better matches the intent of the
NPRM 93-8 proposals, and also harmonizes these sections with JAR-25.
The FAA intends to revise TSO-C26c to be consistent with these
amendments to Sec. 25.735. The Aviation Rulemaking Advisory Committee
(ARAC) has been chartered with recommending appropriate changes to the
TSO. Currently, the FAA envisions issuing the revised TSO, applicable
to transport category airplanes, under a new designation, TSO-C135.
One commenter suggests that the proposed Sec. 25.735(g) should be
deleted. This commenter believes that this proposed flight test
requirement is misplaced in the brake design and construction section
of part 25. The commenter suggests that this issue should be addressed
in the flight test guidance provided in AC 25-7.
The FAA concurs that the proposed flight test requirement would be
better placed elsewhere, but does not concur with completely removing
it from part 25. As stated previously, the FAA considers this test to
be a necessary demonstration of the airplane's ability to safely stop
under the most critical rejected takeoff condition. In addition, the
FAA intends for this test to determine or validate the AFM accelerate-
stop distance for this condition. Therefore, the proposed
Sec. 25.735(g) has been reworded to clarify that the airplane must stop
within the accelerate-stop distance and is adopted as Sec. 25.109(i).
Existing Sec. 25.735(g), which would have been redesignated as
Sec. 25.735(h), remains as Sec. 25.735(g) in the adopted rule.
The FAA received one comment regarding the proposed amendment to
Sec. 25.1587(b). The objective of this proposal is to require that
takeoff performance information for wet runways be included in the AFM.
The commenter agrees with this objective, but notes that
Sec. 25.1587(b) addresses performance information other than that which
would be affected by the surface condition of the takeoff runway. The
commenter suggests that the proposed amendment instead be placed in
Sec. 25.1533(a)(3), which addresses operating limitations based on the
minimum takeoff distances. The FAA concurs with this comment.
Therefore, the proposed change to Sec. 25.1587(b) has been removed, and
Sec. 25.1533(a)(3) is revised accordingly. The adopted amendment also
corrects a typographical error in existing Sec. 25.1533(a), identified
by this commenter, by replacing the reference to Sec. 25.103 with a
reference to Sec. 25.109.
One commenter strongly endorses a requirement to add a takeoff
performance monitor to the flight deck of all airplanes to help pilots
determine whether a takeoff should be rejected or continued. The
commenter notes that modern transport category airplanes already
contain most of the necessary instrumentation. According to the
commenter, all that would be needed would be a display and a dedicated
processor to compute the data to be displayed.
The FAA has participated in past evaluations of systems designed to
monitor the performance of the airplane during the takeoff. Such
systems typically compare the airplane's actual performance, as
determined by airplane instrumentation, with the performance predicted
by the AFM. If the airplane's performance is less than predicted, the
performance shortfall would be indicated by the monitor. In addition,
the takeoff speeds, V1 and VR, could be
correlated with the point on the runway at which they should be
reached. This information could assist pilots in determining whether it
is safer to reject or to continue the takeoff.
The FAA supports efforts at improving the go/no-go decision
process. Advisory Circular 25-15. ``Approval of Flight Management
Systems in Transport Category Airplanes,'' provides a means to obtain
FAA approval of a takeoff performance monitor function as part of a
flight management system. However, takeoff performance monitors are not
yet sufficiently reliable nor are they sophisticated enough to warrant
requiring their addition to the flight deck of transport category
airplanes. Varying winds during the takeoff or a runway with a variable
slope may cause the monitor to provide a false indication. The FAA is
also concerned that the number of high speed rejected takeoffs could
increase as pilots delay action to determine, for example, if an
initially sub-par acceleration is corrected. Also, unnecessary rejected
takeoffs could occur as a result of small
[[Page 8316]]
differences between the predicted airplane acceleration and the actual
airplane's acceleration as determined by the onboard instrumentation. A
takeoff performance monitor would need to consider all of the variables
reflected in the takeoff performance data, such as atmospheric
conditions, airplane flap setting, thrust level (including reduced and
derated takeoff thrust), runway length, slope, and surface condition,
etc. It is possible to design such a system, but current systems have
not demonstrated a safety benefit over the information currently
available to the pilot.
The same commenter recommends that the FAA undertake a study using
research simulators to validate airplane/pilot performance in obstacle
limited takeoffs with engine failures. The objective of this study
would be to determine if there is a high degree of reliability that the
combined airplane/pilot performance is acceptable. The commenter feels
that such a study is essential to considerations of lower screen
heights, tailwind takeoffs, and pilot decision making when the takeoff
weight is limited by obstacle clearance considerations. In the interim,
the commenter suggests that the FAA adopt more stringent obstacle
clearance criteria, such as those contained in the International Civil
Aviation Organization's (ICAO) Annex 6, Attachment C, Paragraph 3--
Takeoff Obstacle Clearance Limitations.
Section 25.111 currently requires applicants to determine the
airplane's takeoff path, which begins with the start of the takeoff
roll and ends approximately 1,500 feet above the takeoff surface. Under
Sec. 25.111(d), applicants must conduct flight tests to ensure that the
airplane can achieve the takeoff path presented in the AFM. The takeoff
path data, and the flight test demonstrations, must be based on the
procedures established by the applicant for operation in service, and
assume that one engine fails at VEF. Except for automatic
propeller feathering and retraction of the landing gear, the airplane
configuration must remain constant, and changes in power or thrust that
require action by a pilot may not be made until the airplane reaches a
height of 400 feet above the takeoff surface.
In addition to the takeoff path determined under Sec. 25.111,
Sec. 25.115 requires applicants to determine the net takeoff flight
path. The net takeoff flight path begins at the end of the takeoff
distance and is equal to the takeoff flight path with the gradient of
climb reduced by: 0.8 percent for two-engine airplanes; 0.9 percent for
three-engine airplanes; and 1.0 percent for four-engine airplanes.
These adjustments to the airplane's demonstrated climb gradient
capability represent a safety margin for use in complying with the
obstacle clearance requirements prescribed by the applicable operating
rules. For airplanes operated under parts 121 or 135, the net takeoff
flight path not only must clear all applicable obstacles, but must
clear them by a height of at least 35 feet.
The current airworthiness standards already address the issues the
commenter proposes for further study. For each part 25 airplane type
design, applicants must conduct flight tests to validate the capability
of the airplane, using normal piloting actions, to achieve the
published flight path. Safety margins are then added to ensure that
this flight path adequately clears all applicable obstacles.
The obstacle clearance criteria recommended by ICAO would require
airplane operators to consider a larger ground area to be under the
takeoff flight path when determining which obstacles must be cleared
vertically. An obstacle that can be considered to be cleared laterally
under current FAA practices may have to be cleared vertically under the
ICAO recommendations. This change could result in restricting the
amount of cargo or passengers to be carried because the airplane's
vertical flight path capability is directly related to its takeoff
weight. The FAA is currently drafting an advisory circular to provide
standardized guidelines regarding the extent of the ground area that
must be considered when determining which obstacles must be cleared
vertically.
Regulatory Evaluation Summary
Proposed changes to Federal regulations must undergo several
economic analyses. First, Executive Order 12866 directs that each
Federal agency shall propose or adopt a regulation only upon a reasoned
determination that the benefits of the intended regulation justify its
costs. Second, the Regulatory Flexibility Act of 1980 requires agencies
to analyze the economic effect of regulatory changes on small entities.
Third, the Office of Management and Budget directs agencies to assess
the effects of regulatory changes on international trade. In conducting
these analyses, the FAA has determined that this rule: (1) Will
generate benefits that justify its costs as defined in the Executive
Order; (2) will not have a significant impact on a substantial number
of small entities; and (3) will not constitute a barrier to
international trade. These analyses, available in the docket, are
summarized below.
In order to analyze the potential net costs of the rule, this
evaluation considers a hypothetical production program for a
representative new type certification. This example assumes that: (1)
Incremental certification costs are incurred in year ``0'', (2)
production starts in year ``4'', (3) the first airplane enters service
in year ``5'', (4) 50 airplanes are produced per year for ten years so
that total production equals 500, (5) each airplane is retired at the
end of its 25 year design service goal, and (6) the discount rate is 7
percent.
The analysis of incremental costs is divided into two cases: one
which assumes a brake design that exhibits little decline in brake
performance with wear, and another which assumes a brake design that
exhibits a decline in brake performance with wear.
In the former case, the average reduction in dry runway accelerate-
stop distance associated with the revised 2-second-at-V1
requirement is greater than the average increase in accelerate-stop
distance associated with the worn brake requirement. This will result
in a reduction in operating costs of approximately $5,105 per airplane
per year, or $128,000 per airplane over its service life (in nominal
terms). However, approximately one third of takeoffs would be conducted
using the wet runway accelerate-stop distance. Under the production run
and cost assumptions enumerated above, the wet runway amendments will
add approximately $2,700 to operating costs per airplane per year, or
$68,000 per airplane over its service life. Therefore, net operating
costs under this design assumption will decline by approximately $2,400
per airplane per year, or $59,400 per airplane over its service life.
Total costs (including consideration of incremental certification and
development costs), then, will be reduced by approximately $28.9
million for the 500 airplane fleet over its 34 year service life. On a
discounted basis, total fleet costs will be reduced by approximately
$7.5 million.
In the case where brake performance is assumed to decline with
wear, the average reduction in dry runway accelerate-stop distance
associated with the revised 2-second-at-V1 requirement is
offset by the average increase in dry runway accelerate-stop distance
associated with the worn brake requirement. Again, however, the wet
runway requirements will add approximately $2,700 (in nominal terms)
per year per airplane to operating costs. Therefore, lifetime
incremental costs (again including consideration of
[[Page 8317]]
incremental certification and development costs) for the 500 airplane
fleet are approximately $34.9 million, or $9.6 million on a discounted
basis. It should be emphasized, however, that FAA anticipates that
future airplane models will incorporate brake designs that exhibit
little reduction in braking force with wear.
The rule will have significant safety implications owing to the
fact that it creates economic incentives for manufacturers, operators,
and airports to adopt procedures which reduce takeoff hazards. While
these ancillary safety benefits are not directly valued in this
economic analysis, they are discussed in a qualitative way below.
The rule's worn-brake provisions will have important safety
impacts. For airplanes that continue to make use of brake designs in
which braking capacity declines with wear, the rule provides an
incentive to reduce the specified level of allowable wear in return for
some reduction in accelerate-stop distances. In this way, accelerate-
stop distances are more closely related to actual brake performance.
Existing regulations do not distinguish between dry and wet runway
surface conditions. The accident history, however, shows that wet
runway rejected takeoff overrun accidents account for a
disproportionate share of the total. In fact, the wet runway rejected
takeoff accident rate (involving substantial damage or hull loss) is
seven times greater than the dry runway accident rate. The rule
enhances safety by taking into account this hazardous takeoff
condition. First, it directly increases accelerate-stop margins for wet
runway conditions. Second, it creates an economic incentive to develop
more stringent maintenance programs for skid-resistant runway surfaces.
Regulatory Flexibility Determination
The Regulatory Flexibility Act of 1980 (RFA) was enacted by
Congress to ensure that small entities are not unnecessarily and
disproportionately burdened by government regulations. The RFA requires
agencies to review rules which may have ``a significant economic impact
on a substantial number of small entities.'' FAA Order 2100.14A,
Regulatory Flexibility Criteria and Guidance, specifies small entity
size and cost thresholds by Standard Industrial Classification (SIC).
Entities potentially affected by the rule include manufacturers of
transport category airplanes (SIC 3721) and operators of aircraft for
hire (SIC 4511).
There are no manufacturers of transport category airplanes that
meet the SIC 3721 size threshold for small entities (75 employees).
However, small air carriers operating transport category airplanes
could be affected by the rule. Order 2100.14A defines a small carrier
as one owning 9 or fewer aircraft. The definition of ``significant
economic impact'' varies by air carrier type: for operators whose
fleets consist entirely of aircraft having a seating capacity of more
than 60 passengers the threshold is $123,445, for other operators the
threshold is $69,005.
Under the most conservative (that is, most costly) compliance
assumptions, the rule will increase operating costs by approximately
$2,700 per airplane per year; or $24,300 per year for a nine-airplane
fleet. Assuming that all incremental certification costs are passed on
to the operator, the rule would increase the price of an airplane by
$1,570. When this is amortized over the 25-year life of the airplane
(assuming a 7% discount rate), the incremental cost per airplane is
approximately $126 per year or $1,134 per year for a nine-airplane
fleet. An upper-bound estimate of the annual impact of the proposed
rule to small operators, then, is approximately $24,300+$1,134=$25,434.
FAA holds, therefore, that the rule will not have a significant
economic impact on a substantial number of small entities.
Unfunded Mandates Reform Act
Title II of the Unfunded Mandates Reform Act of 1995 (the Act),
enacted as Pub. L. 104-4 on March 22, 1995, requires each Federal
agency, to the extent permitted by law, to prepare a written assessment
of the effects of any Federal mandate in a proposed or final agency
rule that may result in the expenditure by State, local, and tribal
governments, in the aggregate, or by the private sector, of $100
million or more (adjusted annually for inflation) in any one year.
Section 204(a) of the Act, 2 U.S.C. 1534(a), requires the Federal
agency to develop an effective process to permit timely input by
elected officers (or their designees) of State, local, and tribal
governments on a proposed ``significant intergovernmental mandate.'' A
``significant intergovernmental mandate'' under the Act is any
provision in a Federal agency regulation that will impose an
enforceable duty upon State, local, and tribal governments, in the
aggregate, of $100 million (adjusted annually for inflation) in any one
year. Section 203 of the Act, 2 U.S.C. 1533, which supplements section
204(a), provides that before establishing any regulatory requirements
that might significantly or uniquely affect small governments, the
agency shall have developed a plan that, among other things, provides
for notice to potentially affected small governments, if any, and for a
meaningful and timely opportunity to provide input in the development
of regulatory proposals.
The rule does not contain any Federal intergovernmental or private
sector mandate. Therefore, the requirements of Title II of the Unfunded
Mandates Reform Act of 1995 do not apply.
Trade Impact Assessment
Recognizing that nominally domestic regulations often affect
international trade, the Office of Management and Budget directs
Federal agencies to assess whether or not a rule or regulation will
have the effect of lessening the restraints of any trade-sensitive
actively. The FAA determines that the subject rule will reduce barriers
to international trade.
The rule collectively places U.S. and foreign transport airplanes
on a more equitable basis regarding their marketability. The
standardization of certification criteria between the FAA and the Joint
Aviation Authorities (JAA) of Europe, and the equalization of safety
levels for pre- and post-Amendment 25-42 airplanes eliminates the
slight comparative disadvantage experienced by certain foreign
airplanes. The requirement regarding the two-second margin allows
European-produced airplanes certified under Amendment 25-42 to become
slightly more competitive against current production U.S. airplanes
that were not certified under Amendment 25-42 by marginally expanding
their takeoff envelope.
Federalism Implications
The regulations adopted herein will not have substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government. Therefore, in
accordance with Executive Order 12612, it is determined that this final
rule will not have sufficient federalism implications to warrant the
preparation of a Federalism Assessment.
International Civil Aviation Organization (ICAO) and Joint Aviation
Regulations
In keeping with U.S. obligations under the Convention on
International Civil Aviation, it is FAA policy to comply with ICAO
Standards and Recommended Practices to the maximum extent practicable.
The FAA has determined that this rule does not
[[Page 8318]]
conflict with any international agreement of the United States.
Paperwork Reduction Act
In accordance with the Paperwork Reduction Act of 1990 (44 U.S.C.
3501 et seq.). there are not reporting or recordkeeping requirements
associated with this rule.
Regulations Affecting Intrastate Aviation in Alaska
Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat.
3213) requires the Administrator, when modifying regulations in Title
14 of the CFR in a manner affecting intrastate aviation in Alaska, to
consider the extent to which Alaska is not served by transportation
modes other than aviation, and to establish such regulatory
distinctions as he or she considers appropriate. Because this final
rule applies to the certification of future designs of transport
category airplane and their subsequent operation, it could affect
interstate aviation in Alaska. The Administrator has considered the
extent to which Alaska is not served by transportation modes other than
a aviation, and how the final rule could have been applied differently
to intrastate operations in Alaska. However, the Administrator has
determined that airplanes operated solely in Alaska would present the
same safety concerns as all other affected airplanes; therefore, it
would be inappropriate to establish a regulatory distinction for the
intrastate operation of affected airplanes in Alaska.
List of Subjects
14 CFR Part 1
Air transportation.
14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
14 CFR Part 91
Aircraft, Airmen, Aviation safety, Reporting and recordkeeping
requirements.
14 CFR Part 121
Air carriers, Aircraft, Airmen, Aviation safety, Charter flights,
Reporting and recordkeeping requirements, Safety, Transportation.
14 CFR Part 135
Aircraft, Airplane, Airworthiness, Air transportation.
Adoption of the Amendment
In consideration of the foregoing, the Federal Aviation
Administration amends 14 CFR parts 1, 25, 91, 121, and 135 of the
Federal Aviation Regulations (FAR) as follows:
PART 1--DEFINITIONS AND ABBREVIATIONS
1. The authority citation for part 1 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
2. Section 1.2 is amended by adding a new abbreviation
``VEF'' and revising the description for the abbreviation
``V1'' to read as follows:
Sec. 1.2 Abbreviations and symbols.
* * * * *
VEF means the speed at which the critical engine is
assumed to fail during takeoff.
* * * * *
V1 means the maximum speed in the takeoff at which the
pilot must take the first action (e.g., apply brakes, reduce thrust,
deploy speed brakes) to stop the airplane within the accelerate-stop
distance. V1 also means the minimum speed in the takeoff,
following a failure of the critical engine at VEF, at which
the pilot can continue the takeoff and achieve the required height
above the takeoff surface within the takeoff distance.
* * * * *
PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
3. The authority citation for part 25 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44704.
4. Section 25.101 is amended by adding a new paragraph (i) to read
as follows:
Sec. 25.101 General.
* * * * *
(i) The accelerate-stop and landing distances prescribed in
Secs. 25.109 and 25.125, respectively, must be determined with all the
airplane wheel brake assemblies at the fully worn limit of their
allowable wear range.
5. Section Sec. 25.105 is amended by revising paragraph (c)(1) to
read as follows:
Sec. 25.105 Takeoff.
* * * * *
(c) * * *
(1) In the case of land planes and amphibians:
(i) Smooth, dry and wet, hard-surfaced runways; and
(ii) At the option of the applicant, grooved or porous friction
course wet, hard-surfaced runways.
* * * * *
6. Section Sec. 25.107 is amended by revising paragraph (a)(2) to
read as follows:
Sec. 25.107 Takeoff speeds.
(a) * * *
(2) V1, in terms of calibrated airspeed, is selected by
the applicant; however, V1 may not be less than
VEF plus the speed gained with critical engine inoperative
during the time interval between the instant at which the critical
engine is failed, and the instant at which the pilot recognizes and
reacts to the engine failure, as indicated by the pilot's initiation of
the first action (e.g., applying brakes, reducing thrust, deploying
speed brakes) to stop the airplane during accelerate-stop tests.
* * * * *
7. Section 25.109 is amended by revising paragraph (a),
redesignating paragraph (b) as paragraph (e) and revising the
introductory text, redesignating paragraph (c) as paragraph (g)
redesignating paragraph (d) as paragraph (h) and revising the first
sentence, and adding new paragraphs (b), (c), (d), (f), and (i) to read
as follows:
Sec. 25.109 Accelerate-stop distance.
(a) The accelerate-stop distance on a dry runway is the greater of
the following distances:
(1) The sum of the distances necessary to--
(i) Accelerate the airplane from a standing start with all engines
operating to VEF for takeoff from a dry runway;
(ii) Allow the airplane to accelerate from VEF to the
highest speed reached during the rejected takeoff, assuming the
critical engine fails at VEF and the pilot takes the first
action to reject the takeoff at the V1 for takeoff from a
dry runway; and
(iii) Come to a full stop on a dry runway from the speed reached as
prescribed in paragraph (a)(1)(ii) of this section; plus
(iv) A distance equivalent to 2 seconds at the V1 for
takeoff from a dry runway.
(2) The sum of the distances necessary to--
(i) Accelerate the airplane from a standing start with all engines
operating to the highest speed reached during the rejected takeoff,
assuming the pilot takes the first action to reject the takeoff at the
V1 for takeoff from a dry runway; and
(ii) With all engines still operating, come to a full stop on dry
runway from the speed reached as prescribed in paragraph (a)(2)(i) of
this section; plus
(iii) A distance equivalent to 2 seconds at the V1 for
takeoff from a dry runway.
[[Page 8319]]
(b) The accelerate-stop distance on a wet runway is the greater of
the following distances:
(1) The accelerate-stop distance on a dry runway determined in
accordance with paragraph (a) of this section; or
(2) The accelerate-stop distance determined in accordance with
paragraph (a) of this section, except that the runway is wet and the
corresponding wet runway values of VEF and V1 are
used. In determining the wet runway accelerate-stop distance, the
stopping force from the wheel brakes may never exceed:
(i) The wheel brakes stopping force determined in meeting the
requirements of Sec. 25.101(i) and paragraph (a) of this section; and
(ii) The force resulting from the wet runway braking coefficient of
friction determined in accordance with paragraphs (c) or (d) of this
section, as applicable, taking into account the distribution of the
normal load between braked and unbraked wheels at the most adverse
center-of-gravity position approved for takeoff.
(c) The wet runway braking coefficient of friction for a smooth wet
runway is defined as a curve of friction coefficient versus ground
speed and must be computed as follows:
(1) The maximum tire-to-ground wet runway braking coefficient of
friction is defined as:
BILLING CODE 4910-13-M
[GRAPHIC] [TIFF OMITTED] TR18FE98.004
BILLING CODE 4910-13-C
Where--
Tire Pressure=maximum airplane operating tire pressure (psi);
t/gMAX=maximum tire-to-ground braking coefficient;
V=airplane true ground speed (knots); and
Linear interpolation may be used for tire pressures other than those
listed.
(2) The maximum tire-to-ground wet runway braking coefficient of
friction must be adjusted to take into account the efficiency of the
anti-skid system on a wet runway. Anti-skid system operation must be
demonstrated by flight testing on a smooth wet runway, and its
efficiency must be determined. Unless a specific anti-skid system
efficiency is determined from a quantitative analysis of the flight
testing on a smooth wet runway, the maximum tire-to-ground wet runway
braking coefficient of friction determined in paragraph (c)(1) of this
section must be multiplied by the efficiency value associated with the
type of anti-skid system installed on the airplane:
------------------------------------------------------------------------
Efficiency
Type of anti-skid system value
------------------------------------------------------------------------
On-Off...................................................... 0.30
Quasi-Modulating............................................ 0.50
Fully Modulating............................................ 0.80
------------------------------------------------------------------------
(d) At the option of the applicant, a higher wet runway braking
coefficient of friction may be used for runway surfaces that have been
grooved or treated with a porous friction course material. For grooved
and porous friction course runways, the wet runway braking coefficent
of friction is defined as either:
(1) 70 percent of the dry runway braking coefficient of friction
used to determine the dry runway accelerate-stop distance; or
(2) The wet runway braking coefficient defined in paragraph (c) of
this section, except that a specific anti-skid system efficiency, if
determined, is appropriate for a grooved or porous friction course wet
runway, and the maximum tire-to-ground wet runway braking coefficient
of friction is defined as:
BILLING CODE 4910-13-M
[[Page 8320]]
[GRAPHIC] [TIFF OMITTED] TR18FE98.005
BILLING CODE 4910-13-C
Where--
Tire Pressure=maximum airplane operating tire pressure (psi);
t/gMAX=maximum tire-to-ground braking coefficient;
V=airplane true ground speed (knots); and
Linear interpolation may be used for tire pressures other than those
listed.
(e) Except as provided in paragraph (f)(1) of this section, means
other than wheel brakes may be used to determine the accelerate-stop
distance if that means--
* * * * *
(f) The effects of available reverse thrust--
(1) Shall not be included as an additional means of deceleration
when determining the accelerate-stop distance on a dry runway; and
(2) May be included as an additional means of deceleration using
recommended reverse thrust procedures when determining the accelerate-
stop distance on a wet runway, provided the requirements of paragraph
(e) of this section are met.
* * * * *
(h) If the accelerate-stop distance includes a stopway with surface
characteristics substantially different from those of the runway, the
takeoff data must include operational correction factors for the
accelerate-stop distance. * * *
(i) A flight test demonstration of the maximum brake kinetic energy
accelerate-stop distance must be conducted with not more than 10
percent of the allowable brake wear range remaining on each of the
airplane wheel brakes.
8. Section 25.113 is amended by revising the introductory text of
paragraph (a) and revising paragraph (a)(1), redesignating paragraph
(b) as paragraph (c) and revising it, and adding a new paragraph (b) to
read as follows:
Sec. 25.113 Takeoff distance and takeoff run.
(a) Takeoff distance on a dry runway is the greater of--
(1) The horizontal distance along the takeoff path from the start
of the takeoff to the point at which the airplane is 35 feet above the
takeoff surface, determined under Sec. 25.111 for a dry runway; or
* * * * *
(b) Takeoff distance on a wet runway is the greater of--
(1) The takeoff distance on a dry runway determined in accordance
with paragraph (a) of this section; or
(2) The horizontal distance along the takeoff path from the start
of the takeoff to the point at which the airplane is 15 feet above the
takeoff surface, achieved in a manner consistent with the achievement
of V2 before reaching 35 feet above the takeoff surface,
determined under Sec. 25.111 for a wet runway.
(c) If the takeoff distance does not include a clearway, the
takeoff run is equal to the takeoff distance. If the takeoff distance
includes a clearway--
(1) The takeoff run on a dry runway is the greater of--
(i) The horizontal distance along the takeoff path from the start
of the takeoff to a point equidistant between the point at which
VLOF is reached and the point at which the airplane is 35
feet above the takeoff surface, as determined under Sec. 25.111 for a
dry runway; or
(ii) 115 percent of the horizontal distance along the takeoff path,
with all engines operating, from the start of the takeoff to a point
equidistant between the point at which VLOF is reached and
the point at which the airplane is 35 feet above the takeoff surface,
determined by a procedure consistent with Sec. 25.111.
(2) The takeoff run on a wet runway is the greater of--
(i) The horizontal distance along the takeoff path from the start
of the takeoff to the point at which the airplane is 15 feet above the
takeoff surface, achieved in a manner consistent with the achievement
of V2 before reaching 35 feet above the takeoff surface, as
determined under Sec. 25.111 for a wet runway; or
(ii) 115 percent of the horizontal distance along the takeoff path,
with all engines operating, from the start of the takeoff to a point
equidistant between the point at which VLOF is reached and
the point at which the airplane is 35 feet above the takeoff surface,
determined by a procedure consistent with Sec. 25.111.
9. Section 25.115 is amended by revising paragraph (a) to read as
follows:
Sec. 25.115 Takeoff flight path.
(a) The takeoff flight path shall be considered to begin 35 feet
above the takeoff surface at the end of the takeoff distance determined
in accordance with Sec. 25.113(a) or (b), as appropriate for the runway
surface condition.
* * * * *
10. Section 25.735 is amended by revising paragraphs (f)
introductory text and (f)(2) and adding a new paragraph (h) to read as
follows:
Sec. 25.735 Brakes
* * * * *
(f) The design landing brake kinetic energy capacity rating of each
main wheel-brake assembly shall be used during qualification testing of
the brake to the applicable Technical Standard Order (TSO) or an
acceptable equivalent. This kinetic energy rating may not be less than
the kinetic energy absorption requirements determined under either of
the following methods:
(1) * * *
(2) Instead of a rational analysis, the kinetic energy absorption
requirements for each main wheel-brake assembly may be derived from the
following formula, which must be modified in cases of designed unequal
braking distributions.
[[Page 8321]]
[GRAPHIC] [TIFF OMITTED] TR18FE98.006
Where--
KE=Kinetic energy per wheel (ft.-lb.);
W=Design landing weight (lb.);
V=Airplane speed in knots. V must not be less than VS0, the
power off stalling speed of the airplane at sea level, at the design
landing weight, and in the landing configuration; and
N=Number of main wheels with brakes.
* * * * *
(h) The rejected takeoff brake kinetic energy capacity rating of
each main wheel-brake assembly that is at the fully worn limit of its
allowable wear range shall be used during qualification testing of the
brake to the applicable Technical Standard Order (TSO) or an acceptable
equivalent. This kinetic energy rating may not be less than the kinetic
energy absorption requirements determined under either of the following
methods:
(1) The brake kinetic energy absorption requirements must be based
on a rational analysis of the sequence of events expected during an
accelerate-stop maneuver. This analysis must include conservative
values of airplane speed at which the brakes are applied, braking
coefficient of friction between tires and runway, aerodynamic drag,
propeller drag or powerplant forward thrust, and (if more critical) the
most adverse single engine or propeller malfunction.
(2) Instead of a rational analysis, the kinetic energy absorption
requirements for each main wheel brake assembly may be derived from the
following formula, which must be modified in cases of designed unequal
braking distributions:
[GRAPHIC] [TIFF OMITTED] TR18FE98.007
Where--
KE=Kinetic energy per wheel (ft.-lb.);
W=Airplane weight (lb.);
V=Airplane speed (knots);
N=Number of main wheels with brakes; and
W and V are the most critical combination of takeoff weight and ground
speed obtained in a rejected takeoff.
11. Section 25.1533 is amended by revising paragraph (a)(3) to read
as follows:
Sec. 25.1533 Additional operating limitations.
(a) * * *
(3) The minimum takeoff distances must be established as the
distances at which compliance is shown with the applicable provisions
of this part (including the provisions of Secs. 25.109 and 25.113, for
weights, altitudes, temperatures, wind components, runway surface
conditions (dry and wet), and runway gradients) for smooth, hard-
surfaced runways. Additionally, at the option of the applicant, wet
runway takeoff distances may be established for runway surfaces that
have been grooved or treated with a porous friction course, and may be
approved for use on runways where such surfaces have been designed
constructed, and maintained in a manner acceptable to the
Administrator.
* * * * *
PART 91--GENERAL OPERATING AND FLIGHT RULES
12. The authority citation for part 91 continues to read as
follows:
Authority: 49 U.S.C. 106(g), 1155, 40103, 40113, 40120, 44101,
44111, 44701, 44709, 44711, 44712, 44715, 44716, 44717, 44722,
46306, 46315, 46316, 46502, 46504, 46506-46507, 47122, 47508, 47528-
47531; Articles 12 and 29 of the Convention on International Civil
Aviation (61 Stat. 1180), 902.
13. Section 91.605 is amended by revising paragraph (b)(3) to read
as follows:
Sec. 91.605 Transport category civil airplane weight limitations.
* * * * *
(b) * * *
(3) The takeoff weight does not exceed the weight shown in the
Airplane Flight Manual to correspond with the minimum distances
required for takeoff, considering the elevation of the airport, the
runway to be used, the effective runway gradient, the ambient
temperature and wind component at the time of takeoff, and, if
operating limitations exist for the minimum distances required for
takeoff from wet runways, the runway surface condition (dry or wet).
Wet runway distances associated with grooved or porous friction course
runways, if provided in the Airplane Flight Manual, may be used only
for runways that are grooved or treated with a porous friction course
(PFC) overlay, and that the operator determines are designed,
constructed, and maintained in a manner acceptable to the
Administrator.
* * * * *
PART 121--OPERATING REQUIREMENTS: DOMESTIC, FLAG, AND SUPPLEMENTAL
OPERATIONS
14. The authority citation for part 121 continues to read as
follows:
Authority: 49 U.S.C. 106(g), 40113, 40119, 44101, 44701-44702,
44705, 44709-44711, 44713, 44716-44717, 44722, 44901, 44903-44904,
44912, 46105.
15. Section 121.189 is amended by revising paragraph (e) to read as
follows:
Sec. 121.189 Airplanes: Turbine engine powered: Takeoff limitations.
* * * * *
(e) In determining maximum weights, minimum distances, and flight
paths under paragraphs (a) through (d) of this section, correction must
be made for the runway to be used, the elevation of the airport, the
effective runway gradient, the ambient temperature and wind component
at the time of takeoff, and, if operating limitations exist for the
minimum distances required for takeoff from wet runways, the runway
surface condition (dry or wet). Wet runway distances associated with
grooved or porous friction course runways, if provided in the Airplane
Flight Manual, may be used only for runways that are grooved or treated
with a porous friction course (PFC) overlay, and that the operator
determines are designed, constructed, and maintained in a manner
acceptable to the Administrator.
* * * * *
PART 135--OPERATING REQUIREMENTS: COMMUTER AND ON-DEMAND OPERATIONS
16. The authority citation for part 135 continues to read as
follows:
Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44705, 44709,
44711-44713, 44715-44717, 44722.
17. Section 135.379 is amended by revising paragraph (e) to read as
follows:
Sec. 135.379 Large transport category airplanes: Turbine engine
powered: Takeoff limitations.
* * * * *
(e) In determining maximum weights, minimum distances, and flight
paths under paragraphs (a) through (d) of this section, correction must
be made for the runway to be used, the elevation of the airport, the
effective runway gradient, the ambient temperature and wind component
at the time of takeoff, and, if operating limitations exist for the
minimum distances required for takeoff from wet runways, the runway
surface condition (dry or wet). Wet runway distances associated with
grooved or porous friction course runways, if provided in the Airplane
Flight Manual, may be used only for runways that are grooved or treated
with a porous friction course (PFC) overlay, and that the operator
determines are designed, constructed, and maintained in a manner
acceptable to the Administrator.
* * * * *
Issued in Washington, DC on February 10, 1998.
Jane F. Garvey,
Administrator.
[FR Doc. 98-3898 Filed 2-17-98; 8:45 am]
BILLING CODE 4910-13-M
