[Federal Register Volume 62, Number 167 (Thursday, August 28, 1997)]
[Rules and Regulations]
[Pages 45523-45526]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-22919]
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Rules and Regulations
Federal Register
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Federal Register / Vol. 62, No. 167 / Thursday, August 28, 1997 /
Rules and Regulations
[[Page 45523]]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM-134; Special Conditions No. 25-ANM-131]
Special Conditions: Empresa Brasileira de Aeronautica S.A.,
(EMBRAER) Model EMB-145 Airplane; Thrust Reverser Systems
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are for the Empresa Brasileira de
Aeronautica S.A., (EMBRAER) Model EMB-145 airplane. This airplane will
have a novel or unusual design feature associated with thrust reversers
as optional equipment. These special conditions contain the additional
safety standards which the Administrator considers necessary to
establish a level of safety equivalent to that established by the
airworthiness standards of part 25 of the Federal Aviation Regulations
(FAR).
EFFECTIVE DATE: September 29, 1997.
FOR FURTHER INFORMATION CONTACT: Colin Fender, FAA, Flight Test and
Systems Branch of the Transport Standards Staff, ANM-111, Transport
Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue
SW, Renton, Washington 98055-4056; telephone 425-227-2191.
SUPPLEMENTARY INFORMATION:
Background
Embraer first made application for a U.S. Type Certificate for the
Model EMB-145 on August 30, 1989, to the FAA Atlanta Aircraft
Certification Office through the Brazilian Centro Tecnico Aeroespacial
(CTA). On June 2, 1992, Embraer filed for an extension of that
application. The EMB-145 is a 50 passenger, pressurized, low-winged,
``T'' tailed, transport category airplane with retractable tricycle
type landing gear. The airplane is powered by two Allison Model AE3007A
high bypass ratio turbofan engines mounted on the aft fuselage, which
are controlled by a Full Authority Digital Engine Control (FADEC). The
cockpit will include a complete set of Electronic Flight
Instrumentation and Engine Indication and Crew Alerting Systems (EFIS
and EICAS).
Embraer has proposed to certificate and market the EMB-145 with
thrust reversers as optional equipment. Thrust reversers have been
shown to play a significant role in reducing accelerate-stop distances
on wet and contaminated runways and have contributed to the transport
category airplane fleet's accelerate-stop safety record.
The establishment of the transport category airplane safety record,
with regard to accelerate-stop and landing overruns, is tied to the
availability of auxiliary braking means that are independent of wheel-
brake, tire, and runway surface interaction. On early transport
category airplanes with propellers driven by reciprocating engines or
turbine powerplants, auxiliary braking was provided by commanding the
propellers to a reverse pitch position, causing a deceleration, rather
than acceleration, of air through the propeller disk. Due to the large
diameter of the propellers, this was quite an effective braking means.
Though these early transports did not have the high operating speeds of
today's jet fleet, they also did not benefit from the sophisticated
wheel-brake antiskid systems available today. As runway friction
conditions degrade to those associated with a surface covered by ice,
even today's antiskid systems will provide little in the way of
stopping force. As runway friction conditions degrade, the braking
contribution of reverse pitch systems increases considerably.
As the first generation turbojet-powered transport category
airplanes went into service in the latter half of the 1950s, thrust
reverser systems were developed to provide this same type of auxiliary
braking as reverse pitch propellers by reversing the engine exhaust
flow. As powerplant technology evolved and low bypass ratio turbofan
engines entered commercial service in the early 1960's, thrust
reversers were developed to reverse both the fan and core exhaust
flows, thus maintaining the availability of auxiliary braking. With the
advent of large high bypass ratio turbofan engines in the late 1960s,
many thrust reverser systems reversed the fan exhaust flow only, which
provided a substantial auxiliary braking effect due to the majority of
the total inlet flow going through the fan section. Numerous test
programs, by both research organizations and aerospace manufacturers,
have substantiated the increased stopping benefit provided by thrust
reversers as runway surface friction conditions deteriorate.
The vast majority of jet-powered transport category airplanes in
service have been of the large, passenger carrying variety. Research
shows that with the exception of a very limited number of airplane
types, some of which had considerably slower takeoff and landing speeds
than their counterparts, all these large, passenger carrying, turbojet/
turbofan-powered transports included thrust reverser systems as part of
their basic design (i.e., as standard equipment). The last such
aircraft certified without thrust reversers as part of the basic design
was the British Aerospace 146 (BAe 146) in 1983. When the sheer
numerical majority of these large transports is combined with their
high-use operating environment, often requiring takeoffs and landings
to be made on slippery runway surfaces, it is clear that thrust
reversers must have played a role in establishing their excellent
safety record.
It should also be noted that as the number of small transport
category airplanes in service has increased, notably corporate jets and
regional airliners, there has been an increasing tendency for these
airplanes to be equipped with some type of thrust reversing system.
Nearly all the regional airliners are turbopropeller-powered with
reverse pitch capability, and an increasing number of corporate jets
include thrust reversers as standard equipment.
The accelerate-stop and landing distances presented in the FAA
approved Airplane Flight Manual (AFM) are determined from measurements
of the various influential parameters taken during certification flight
tests. These flight tests are
[[Page 45524]]
accomplished by FAA test pilots (or manufacturers' Designated
Engineering Representative (DER) test pilots) under controlled
conditions on dry runways. In the operational environment, even on dry
runways, the ability of an airplane to match the AFM accelerate-stop
performance is based on many factors, including the correct and timely
execution of procedures by the pilot and maximum stopping performance
being available from the wheel braking system. As runway surface
conditions degrade to wet, contaminated, or icy, the accompanying
reduction in available friction will result in an increase in stopping
distances, causing the wet runway accelerate-stop distances to exceed
the dry runway accelerate-stop distances published in the AFM.
Obviously, if the takeoff is runway length-limited as determined from
the dry runway AFM accelerate-stop distances, and the runway surface is
anything but dry, the probability for an overrun accident is increased
significantly. (This increased risk factor is acknowledged for the
landing scenario in part 121, the operating rules for air carriers and
commercial operators of large aircraft, which requires an increase in
the landing field length required for landings on wet runways.)
In the operating conditions described above, any additional braking
means, such as thrust reversers, will be beneficial. This is
particularly true since the braking contribution of reverse thrust
increases as runway surface friction decreases. This inverse
relationship between reverse thrust braking contribution and runway
surface friction is further enhanced as ground speed increases.
Since 1990 the Transport Airplane Directorate (TAD) has been
developing new part 25 accelerate-stop criteria that includes
accountability for the degradation in stopping force due to wet runway
surfaces. Test results obtained from several research organizations
showed a fixed stopping distance factor of two, relative to dry runway
stopping distances, to be representative of what could be expected in
normal operations. The proposed accelerate-stop standards, published as
Notice of Proposed Rulemaking (NPRM) 93-8, assumed a similar
degradation in braking by prescribing a wet/dry braking coefficient of
friction ratio of one-half (i.e., WET = 0.5 DRY) as
the primary basis for calculating wet runway accelerate-stop distances.
An integral part of the proposed wet runway accelerate-stop rule is
credit for the amount of reverse thrust available (provided certain
reliability and controllability criteria are met).
The accelerate-stop certification basis for the EMB-145 is
Sec. 25.109, as amended by Amendment 25-42, effective March 1, 1978.
Thrust reversing systems are not required by the FAR and, when
installed, no performance credit is granted for their availability in
the dry runway accelerate-stop distances required by Sec. 25.109, as
amended by Amendment 25-42, effective March 1, 1978. However, the vast
majority of transport category airplanes in service at the time the
regulatory changes of Amendment 25-42 were promulgated were equipped
with thrust reversers. Consequently, the certification of transport
category airplanes intended to be operated in Part 121-type commercial
service without thrust reversers was not envisaged at the time
Amendment 25-42 was promulgated.
In consideration of the intended operation of the EMB-145, the FAA
considers the non-inclusion of thrust reversers into the basic airplane
to be an unusual design feature that is not adequately addressed by the
airworthiness regulations of part 25, and therefore proposes to apply
special conditions to the EMB-145 in accordance with Sec. 21.16. In
accordance with the preamble material to Amendment 25-54 (page 274),
addressing the definition of a novel or unusual design feature (as used
in Sec. 21.16), the non-inclusion of thrust reversers in the basic EMB-
145 design can be considered a ``novel or unusual design feature''
since such designs were not envisaged at the time the current
airworthiness standard (i.e., Sec. 25.109, Amendment 25-42) was
developed. This application requires the development of requirements
not fully addressed by part 25 nor by any published FAA guidance.
These special conditions provide all the necessary requirements to
determine acceptability of the EMB-145 without the incorporation of
thrust reversers.
Type Certification Basis
Under the provisions of 14 CFR 21.17, Empresa Brasileira de
Aeronautica S.A. must show that the Model EMB-145 meets the applicable
provisions of part 25, as amended by Amendments 25-1 through 25-84.
In addition to the applicable airworthiness regulations and special
conditions, the Model EMB-145 must comply with the fuel vent and
exhaust emission requirements of 14 CFR part 34 and the noise
certification requirements of 14 CFR part 36, and the FAA must make a
finding of regulatory adequacy pursuant to section 611 of Public Law
92-574, the ``Noise Control Act of 1972.''
If the Administrator finds that the applicable airworthiness
regulations (i.e., part 25 as amended) do not contain adequate or
appropriate safety standards for the Model EMB-145 because of a novel
or unusual design feature, special conditions are prescribed under the
provisions of Sec. 21.16.
Special conditions, as appropriate, are issued in accordance with
Sec. 11.49 after public notice, as required by Secs. 11.28 and
11.29(b), and become part of the type certification basis in accordance
with Sec. 21.17(a)(2).
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other model that incorporates the same novel or
unusual design feature, these special conditions would also apply to
the other model under the provisions of Sec. 21.101(a)(1).
Novel or Unusual Design Features
The Model EMB-145 will have an unusual design feature which is the
lack of incorporation of thrust reversers as standard equipment.
Discussion of Comments
Notice of Proposed Special Conditions No. SC-96-7-NM for the
Empresa Brasileira de Aeronautica S.A., (EMBRAER) Model EMB-145, was
published in the Federal Register on November 18, 1996. Three
commenters submitted comments.
All commenters state the special conditions are inappropriate since
thrust reversers are not required for part 25 certification and part 25
airplanes not equipped with thrust reversers have exhibited the same
level of safety as those with thrust reversers. The FAA does not
contest the fact that part 25 does not require thrust reversers. With
regard to the level of safety issue, it is obvious that the additional
braking provided by reverse thrust will always improve safety, and the
amount of that improvement will increase with decreasing runway surface
friction. The only accelerate-stop performance information required to
be in the Airplane Flight Manual (AFM) by the current part 25
airworthiness regulations is based on a dry runway surface; these dry
runway accelerate-stop distances may (and will) be used with no
adjustments for takeoffs made on wet and contaminated runways. This
could be of critical importance for an airplane the size of the EMB-
145, which in all likelihood will see a sizable number of operations on
relatively short
[[Page 45525]]
runways, thus increasing the probability of its being dry runway
takeoff or landing field length-limited.
One commenter states that the main consideration of the special
conditions is that the non-inclusion of thrust reversers is classified
as an unusual design feature because the EMB-145 is intended for
operation in part 121-type commercial service. Consequently, the
commenter states the special conditions are not appropriate under part
25 since the certification basis is independent of the rules an
airplane might be operated under. The FAA does not agree with the
commenter's statement. The overall operational safety of an airplane is
as much the concern of the Aircraft Certification Service of the FAA as
it is the Flight Standards Service, particularly where aircraft
performance is a consideration since it is the Aircraft Certification
Service personnel who witness the flight testing and approve the
resulting Airplane Flight Manual performance that scheduled operations
will be based on.
Similarly, another commenter states that if performance credit is
of established benefit in part 121-type commercial operations, the
appropriate rule to require thrust reversers would be under part 121
and not the certification rules (i.e., part 25). The FAA questions the
use of the term ``performance credit'' since no performance credit has
been given in the past, as discussed in the preceding paragraph. The
FAA understands this comment to mean if thrust reversers have provided
benefits in part 121-type operations, then any rule to require their
installation should be proposed under part 121. The FAA disagrees with
this comment. The FAA's job is to ensure the safety of the traveling
public; whether that is done through the Aircraft Certification Service
or the Flight Standards Service is irrelevant in this case. As
discussed in the notice of proposed special conditions, the thrust
reverser issue is addressed in this context because the FAA has found
that Embraer's type certificate application presents a novel or unusual
design feature for which the applicable airworthiness standards do not
provide adequate safety standards. In accordance with 14 CFR
Sec. 21.16, special conditions are the appropriate mechanism for
dealing with such issues.
One commenter states that if the FAA considers the increased
stopping benefit provided by thrust reversers as substantiation (sic)
for requiring their installation, then performance credit should be
granted for their use. The FAA has for many years gone on record as
being opposed to granting general performance credit for the use of
thrust reversers. One of the primary reasons for this position is that
thrust reversers provided some compensation for the minimal amount of
conservatism assumed in determining the accelerate-stop distances that
takeoffs will be predicated on rejected takeoff accident data indicate
that pilots do not always recognize and respond to a failure condition
at or near V1 in the time period assumed in calculating the
AFM accelerate-stop distances. The FAA has proposed to grant
performance credit for thrust reversers in the determination of
accelerate-stop distances on wet runways, provided the stopping
distances are based on the associated reduced wheel-brake stopping
force available and certain reliability and controllability criteria
are met.
One commenter notes that the proposed special conditions do not
address the Master Minimum Equipment List (MMEL) allowance for
airplanes to have thrust reversers rendered inoperative, and that the
FAA did not consider the economic implications of this issue. The FAA
does not consider this to be a relevant argument against requiring the
installation of thrust reversers on the EMB-145. The MMEL allowance
referred to by the commenter is classified as Level C which, among
other things, places a 10-day limitation on the thrust reversers being
inoperative. The 10-day limitation is, in part, based on the
probability of occurrence of a situation in which the additional
braking force provided by reverse thrust would be beneficial.
One commenter states that the inclusion of a proposed rule (i.e.,
NPRM 93-8) as a certification requirement was not appropriate. A
related comment from another commenter noted that FAA's Aircraft
Certification Service management has stated the FAA would not invoke
unadopted regulations or policy on active certification programs. The
FAA is not mandating compliance with the criteria of NPRM 93-8 as a
certification requirement. Embraer has the option of installing thrust
reversers on the airplane and determining accelerate-stop distances in
accordance with part 25 at the amendment level described in the type
certification basis for the EMB-145. It should also be noted that in
ongoing certification programs, the FAA Transport Airplane Directorate
routinely considers proposed rules as showing an equivalent level of
safety to existing part 25 regulations.
One commenter also states that NPRM 93-8 is not harmonized with the
European Joint Aviation Authorities (JAA) requirements. This statement
is incorrect. The criteria of NPRM 93-8 was developed in conjunction
with the JAA; requirements identical to those of NPRM 93-8 can be found
in the equivalent AAA Notice of Proposed Amendment.
One commenter requests the FAA submit this major change in
certification philosophy to the appropriate regulatory/industry forum.
The FAA discussed the philosophy embodied in Notice No. SC-96-7-NM with
flight test specialists from several foreign civil airworthiness
authorities during its development. The FAA is within its legal bounds
by treating airplanes on a case-by-case basis with special conditions
in accordance with Sec. 21.16. The FAA does not believe it is necessary
to submit the certification philosophy embodied in Notice No. SC-96-7-
NM to a regulatory/industry forum since the wet runway accelerate-stop
criteria in NPRM 93-8, which gives performance credit for available
reverse thrust on wet runways, will encourage manufacturers to
incorporate thrust reversers as part of the basic design of their
airplanes.
One commenter states that the FAA's contention that thrust
reversers have played a significant role in the safety record of
transport category airplanes is not supported by any form of factual
information or data. The FAA disputes this commenter's position. A
significant amount of testing has been conducted over the last 40 years
that has repeatedly proven the increased benefit of reverse thrust as
the runway surface condition deteriorates in terms of available wheel-
braking force. It is obviously difficult to point at a particular
rejected takeoff as an example since any successful field length-
limited RTO that may have occurred on a wet or contaminated runway,
whose takeoff weight was limited by a dry runway accelerate-stop
distance, would not have been recorded. However, it stands to reason
that the probability of such a case occurring would be very low without
the additional braking force contribution provided by thrust reversers.
As discussed above, these special conditions are applicable to the
EMB-145. Should Empresa Brasileira de Aeronautica S.A. apply at a later
date for a change to the type certificate to include another model
incorporating the same novel or unusual design feature, the special
conditions would apply to that model as well under the provisions of
Sec. 21.101(a)(1).
Conclusion: This action affects only certain novel or unusual
design features on one model of airplane. It is not a rule of general
applicability, and it affects only the manufacturer who applied to
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the FAA for approval of these features on the airplane.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Federal Aviation Administration,
Reporting and recordkeeping requirements.
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44704.
The Special Conditions
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special conditions are issued as part of
the type certification basis for the Empresa Brasileira de Aeronautica
S.A., Model EMB-145 airplanes not equipped with thrust reversers.
1. The effect of wet runway surfaces on accelerate-stop distances
for the Model EMB-145 must be accounted for in accordance with the
criteria contained in NPRM 93-8 and its associated guidance.
2. Takeoff limitations for operation of the EMB-145 on wet runway
surfaces must be predicated on the wet runway accelerate-stop criteria
contained in NPRM 93-8.
Issued in Renton, Washington, on August 18, 1997.
Stewart R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service, ANM-100.
[FR Doc. 97-22919 Filed 8-27-97; 8:45 am]
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