[Federal Register Volume 60, Number 167 (Tuesday, August 29, 1995)]
[Proposed Rules]
[Pages 44998-45003]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-21012]
[[Page 44997]]
_______________________________________________________________________
Part IV
Department of Transportation
_______________________________________________________________________
Federal Aviation Administration
_______________________________________________________________________
14 CFR Part 25
Revised Structural Loads Requirements for Transport Category Airplanes;
Proposed Rule
Availability of Proposed Advisory Circular 25.335-1; Notice
Federal Register / Vol. 60, No. 167 / Tuesday, August 29, 1995 /
Proposed Rules
[[Page 44998]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. 28312; Notice No. 95-14]
RIN 2120-AF70
Revised Structural Loads Requirements for Transport Category
Airplanes
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed rulemaking.
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SUMMARY: This notice proposes to revise the structural loads design
requirements of the Federal Aviation Regulations (FAR) for transport
category airplanes by incorporating changes developed in cooperation
with the Joint Aviation Authorities (JAA) of Europe and the Aviation
Rulemaking Advisory Committee (ARAC). This action is necessary because
differences between current U.S. and European requirements impose
unnecessary costs on airplane manufacturers. This action would make
some of the requirements more rational and eliminate differences
between current U.S. and European requirements that impose unnecessary
costs on airplane manufacturers. These proposals are intended to
achieve common requirements and language between the requirements of
the U.S. regulations and the Joint Aviation Requirements (JAR) of
Europe while maintaining at least the level of safety provided by the
current regulations.
DATES: Comments must be received on or before November 27, 1995.
ADDRESSES: Comments on this notice may be mailed in triplicate to:
Federal Aviation Administration (FAA), Office of the Chief Counsel,
Attention: Rules Docket (AGC-200), Docket No. 28312, 800 Independence
Avenue SW., Washington, DC 20591; or delivered in triplicate to: Room
915G, 800 Independence Avenue SW., Washington, DC 20591. Comments
delivered must be marked Docket No. 28312. Comments may be examined in
Room 915G weekdays, except Federal holidays, between 8:30 a.m. and 5
p.m. In addition, the FAA is maintaining an information docket of
comments in the Transport Airplane Directorate (ANM-100), FAA, 1601
Lind Avenue SW., Renton, WA 98055-4056. Comments in the information
docket may be examined weekdays, except Federal holidays, between 7:30
a.m. and 4 p.m.
FOR FURTHER INFORMATION CONTACT:
James Haynes, Airframe and Propulsion Branch, ANM-112, Transport
Airplane Directorate, Aircraft Certification Service, FAA, 1601 Lind
Avenue SW., Renton, WA 98055-4056; telephone (206) 227-2131.
SUPPLEMENTARY INFORMATION
Comments Invited
Interested persons are invited to participate in this proposed
rulemaking by submitting such written data, views, or arguments as they
may desire. Comments relating to any environmental, energy, or economic
impact that might result from adopting the proposals contained in this
notice are invited. Substantive comments should be accompanied by cost
estimates. Commenters should identify the regulatory docket or notice
number and submit comments in triplicate to the Rules Docket address
above. All comments received on or before the closing date for comments
will be considered by the Administrator before taking action on this
proposed rulemaking. The proposals contained in this notice may be
changed in light of comments received. All comments received will be
available in the Rules Docket, both before and after the comment period
closing date, for examination by interested persons. A report
summarizing each substantive public contact with FAA personnel
concerning this rulemaking will be filed in the docket. Persons wishing
the FAA to acknowledge receipt of their comments must submit with those
comments a self-addressed, stamped postcard on which the following
statement is made: ``Comments to Docket No. 28312.'' The postcard will
be date/time stamped and returned to the commenter.
Availability of NPRM
Any person may obtain a copy of this notice by submitting a request
to the Federal Aviation Administration, Office of Public Affairs,
Attention: Public Inquiry Center, APA-230, 800 Independence Avenue SW.,
Washington, DC 20591; or by calling (202) 267-3484. Communications must
identify the notice number of this NPRM. Persons interested in being
placed on a mailing list for future rulemaking documents should also
request a copy of Advisory Circular No. 11-2A, Notice of Proposed
Rulemaking Distribution System, which describes the application
procedure.
Background
The manufacturing, marketing and certification of transport
airplanes is increasingly an international endeavor. In order for U.S.
manufacturers to export transport airplanes to other countries the
airplane must be designed to comply, not only with the U.S.
airworthiness requirements for transport airplanes (14 CFR part 25),
but also with the transport airworthiness requirements of the countries
to which the airplane is to be exported.
The European countries have developed a common airworthiness code
for transport category airplanes that is administered by the JAA of
Europe. This code is the result of a European effort to harmonize the
various airworthiness codes of the European countries and is called the
Joint Aviation Requirements (JAR)-25. It was developed in a format
similar to 14 CFR part 25. Many other countries have airworthiness
codes that are aligned closely to part 25 or to JAR-25, or they use
these codes directly for their own certification purposes.
Although JAR-25 is very similar to part 25, there are differences
in methodologies and criteria that often result in the need to address
the same design objective with more than one kind of analysis or test
in order to satisfy both part 25 and JAR airworthiness codes. These
differences result in additional costs to the transport airplane
manufacturers and additional costs to the U.S. and foreign authorities
that must continue to monitor compliance with a variety of different
airworthiness codes.
In 1988, the FAA, in cooperation with the JAA and other
organizations representing the U.S. and European aerospace industries,
began a process to harmonize the airworthiness requirements of the
United States with the airworthiness requirements of the European
authorities. The objective was to achieve common requirements for the
certification of transport category airplanes without a substantive
change in the level of safety provided by the regulations. Other
airworthiness authorities such as Transport Canada have also
participated in this process.
In 1992, the harmonization effort was undertaken by the Aviation
Rulemaking Advisory Committee (ARAC). By notice in the Federal Register
(58 FR 13819, March 15, 1993), the FAA chartered a working group of
industry and government structural loads specialists from Europe, the
United States, and Canada. The harmonization effort has now progressed
to a point where some specific proposals have been developed by the
working group for the structural loads requirements of Subpart C of
part 25, ``Structure,'' and these proposals have been recommended to
FAA by letter dated February 2, 1995. This notice contains some of the
proposals necessary to achieve harmonization for
[[Page 44999]]
the loads requirements of part 25. The ARAC working group is also
considering other changes to the loads requirements that may become
proposals for future rulemaking.
Certain technical differences in the part 25 and JAR-25 structural
requirements have resulted in extensive revision or redevelopment of
the criteria and methodology for specific requirements and some of
those issues will be made the subject of separate proposals. In
addition, some standards were already in the process of revision and
improvement by the FAA when the harmonization effort was initiated.
These changes have also been subjected to the harmonization process and
will be proposed in separate notices.
This notice provides many of the proposals necessary for
harmonizing the loads requirements of Subpart C of part 25. Many of the
sections of part 25 that would be changed by this notice are also
affected by an earlier related proposal ``Revised Discrete Gust Load
Design Requirements,'' Notice No. 94-29 (59 FR 47756, September 15,
1994), and the proposals presented here were developed under the
presumption that proposal would be adopted. The final rule text of
Notice No. 94-29, if adopted, will be taken into account in the
drafting of the final rule resulting from the proposals presented in
this NPRM.
A comparison of the proposals in this NPRM with the current version
of JAR-25 may not show identical wording between the proposed part 25
sections and the equivalent JAR-25 sections since, in many cases,
proposals are being made to change both the FAR and the JAR versions at
the same time. However, the proposals in this notice, when taken in
context with the Notices of Proposed Amendment (NPA) currently proposed
by the JAA and FAA Notice No. 94-29, will harmonize the bulk of the
requirements of Subpart C of part 25 and Subpart C of JAR-25.
Discussion
The pitching maneuver resulting from the maximum deflection of the
control surface is specified in Sec. 25.331(c)(1). This maneuver is
commonly known as the ``unchecked'' pitching maneuver since it is not
arrested by an opposite control input. Differences in the terminology
used in part 25 and JAR-25 have led to differences in the way the rule
has been applied. The FAA has interpreted this as a maneuver that
applies to the entire airplane and that must be carried out until the
normal load factor is reached. Consequently, this maneuver could result
in high pitching rates that may be important in determining gyroscopic
loads resulting from rotating machinery such as propellers and large
fans. The equivalent JAR paragraph, however, allows the maneuver to be
terminated when the maximum tail load is reached, and the JAR rule has
been interpreted as primarily applying to the determination of
empennage loads.
It is proposed that Sec. 25.331(c)(1) be revised to specifically
allow the ``unchecked maneuver'' to be terminated when the tail load
reaches a maximum. The maneuver and resulting loads would still be
considered to apply to the entire airplane but, for the purposes of
determining these airplane loads, the maneuver could be terminated when
the maximum tail load is reached. However, for the purpose of
determining the pitching rate used in calculating the gyroscopic loads
of Sec. 25.371, the rule would require the maneuver to be carried out
until the maximum limit load factor on the airplane is reached. In this
regard, another revision to Sec. 25.371 is proposed as discussed below.
These changes would have no impact on safe flight of the airplane, but
would reduce the extent of calculations needed for determining the
critical design loads.
Section 25.335(a)(2) would be revised by replacing the 43 knot
speed margin between the design speed for maximum gust intensity
(VB) and the design cruising speed (VC) with a variable
margin based on the variation of gust speeds with altitude. This new
margin would be approximately equal to 43 knots at sea level and would
vary proportionally to the gust velocities specified in
Sec. 25.34(a)(4) of Notice No. 94-29, Revised Discrete Gust Load Design
Requirements (59 FR 47756 at 47760, September 16, 1994). An alternative
margin established by a rational investigation, provided for in the
current rule, would no longer be allowed since the proposed criteria
are considered to provide the minimum acceptable margin between VB
and VC. Since this proposal provides specific speed margins
equivalent to those currently accepted by rational analyses, there
would be no impact on safety.
Section Sec. 25.335(b)(2) would be revised by increasing the
minimum speed margin for atmospheric variations from 0.05 Mach to 0.07
Mach. Studies by industry have shown that for a conventional aircraft,
a margin of approximately 0.07 Mach is necessary to account for
atmospheric disturbances. However, it is recognized that some aircraft
may have aerodynamic characteristics that would allow a lower margin,
provided a rational analysis of the effects of atmospheric disturbances
is carried out for the airplane. The ARAC believes the 0.07 Mach margin
to be the minimum safe margin unless a rational analysis of the
response of the airplane to atmospheric disturbances justifies a lower
value. The change is intended to provide a harmonized requirement since
a parallel change is being proposed by the JAA in NPA 25C-260. This
proposal would allow the minimum margin to be reduced to the level of
the current rule (0.05 Mach) if a rational analysis warrants such
reduction. Since margins as low as the current margins would still be
allowed, if justified, this proposal would not have a significant
impact on design. In addition to the amendments to part 25 proposed in
this notice, an advisory circular (AC 25.335-1) is being proposed to
ensure that the harmonized standards would be interpreted and applied
consistently. This proposed AC would provide a means of demonstrating
compliance with the provisions of part 25 related to the minimum speed
margin between design cruise speed and design dive speed for transport
category airplanes. Public comments concerning the proposed AC are
invited by separate notice published elsewhere in this issue of the
Federal Register.
Section 25.345(d) would be revised to specify more clearly the
design conditions for wing flaps and similar high lift devices in the
landing configuration. It would be revised to make it clear that this
is a maneuvering flight condition and not an actual ground landing
condition.
In Notice No. 94-29, Revised Discrete Gust Load Design Requirements
(59 FR 47756 at 47760, September 16, 1994), the FAA proposed to remove
the gust conditions from the yawing conditions specified in
Sec. 25.351. This notice proposes to further revise Sec. 25.351, by
allowing the 300-pound pilot effort load to be reduced linearly between
the design maneuvering speed (VA) and VC to 200 pounds at
VC. The current Sec. 25.351 requires 300 pounds to be withstood up
to the design dive speed, VD. Further clarifying changes are also
proposed to eliminate confusion concerning the specific design cases
required by this section. These proposals would make Sec. 25.351 of
part 25 equivalent to Sec. 25.351 of JAR-25 as proposed by the NPA 25C-
260. The change would have little effect on most transport category
airplanes since they usually have devices that limit the effect of
rudder control force on surface deflection. The control pedals and
affected systems would still be designed to comply with the 300 pound
condition at VA. In any case, the requirement to
[[Page 45000]]
withstand 300 pounds at all speeds up to the maximum design dive speed
is considered by the ARAC to be excessive and unrealistic for modern
transport category airplanes. As reflected in the NPRM, the FAA agrees.
Seciton 25.363 concerning side loads on engine mounts would be
revised to clarify that it applies to auxiliary power units as well as
engines. This clarifying proposal would have no impact on safety
because it is consistent with current design practice for transport
category airplanes.
Section 25.371 concerning gyroscopic loads would be revised as
noted above in the discussion of the pitching maneuver of
Sec. 25.331(c)(1). In addition, this notice proposes to require that
the highest pitching rates derived from all rational flight and landing
conditions be used to determine the gyroscopic loads. This proposal
would provide some improvement in safety since the pitching rates
required for calculating the gyroscopic loads would include landing
conditions. Furthermore, to harmonize with the current Sec. 25.371 of
JAR-25, this section would be revised to clarify that it applies to
auxiliary power units as well as engines.
Although Sec. 25.415 ``Ground gust conditions'' is currently
identical in part 25 and JAR-25, this notice proposes to increase the
ground gust velocity from the current maximum of 88 feet per second
(about 52 knots) to 65 knots. JAR-25 currently has a requirement
(Sec. 25.519) that covers ground loads during jacking and tie-down.
Section 25.519 of JAR-25 establishes a 65-knot wind speed for ground
gusts during jacking and tie-down and specifically requires these gusts
to be applied to the control surfaces, rendering the current
Sec. 25.415 of part 25 and JAR-25 ``Ground gust conditions''
inconsistent with Sec. 25.519 of JAR-25 and inconsequential for design.
The FAA has a new requirement similar to Sec. 25.519 of JAR-25. This
requirement, Sec. 25.519 (59 FR 22100, April 28, 1994), is equivalent
to the Sec. 25.519 of JAR-25 except that the control surfaces are not
specified in Sec. 25.519. The FAA has determined that control surfaces
should continue to be addressed only under Sec. 25.415 so this section
is being revised to achieve the same effect as the Sec. 25.519 of JAR-
25 by incorporating the 65-knot wind speed into Sec. 25.415. The
formula presented in Sec. 25.415 would also be simplified in that the
65-knot wind speed would be contained within the numerical constant
(14.3) for the formula used to calculate the ground gust load. These
changes are made for the purpose of clarity and harmonization and would
have not impact on safety.
This notice proposes to revise and reorganize Secs. 25.473, 25.479
and 25.481 and 25.485 in order to clarify the requirement that
structural dynamic effects in the landing conditions be considered and
to clarify which requirements are full airplane rational design
conditions and which are static design loading cases. These proposals
would provide identical language for these sections of part 25 and JAR-
25. The requirement for consideration of dynamic landing conditions is
currently expressed in Sec. 25.473(e) of JAR-25 by specific language,
and in Sec. 25.305(c) of the FAR by general language. The change
proposed in this notice would make it a specific requirement in part
25.
This notice proposes to add a new requirement in Sec. 25.479 to
consider lateral drift in the landing condition. The current JAR
requirement (Sec. 25.479(c)(4)), which covers this subject, would be
incorporated into paragraph (d)(2) of the proposed Sec. 25.479. This is
a rational airplane load requirement that would be in addition to the
requirements of Sec. 25.485 that include specified side loads on the
landing gear. These proposed requirements would have no impact on
safety since they are equivalent to existing requirements and are
consistent with the current design practice for transport airplanes.
Although the language for Sec. 25.483 of part 25 and Sec. 25.483 of
JAR-25 are currently identical, differences in interpretation have
occurred. This notice proposes to clarify the language to define the
requirement as a ``one gear'' landing condition instead of a ``one
wheel'' condition in order to resolve confusion that arises in treating
multi-wheeled landing gear units. The rule would be retitled ``One gear
landing'' and the language in the rule would be revised to reflect this
terminology. An identical change to JAR-25 will be proposed.
Section 25.491 would be revised to eliminate differences in
interpretation and to clarify that it applies equally to takeoff, taxi
and landing roll by changing the title to ``Taxi, takeoff and landing
roll.'' In addition, the reference to Sec. 25.235 would be eliminated
and the language of Sec. 25.235 would be incorporated directly into the
rule.
The requirements concerning nose-gear steering are different
between part 25 and JAR-25 in that Sec. 25.499(e) of JAR-25 requires a
factor of 1.33 on the maximum steering torque and also for the vertical
ground reaction that is combined with the steering torque. This factor
is applied in addition to the 1.5 safety factor normally applied to
limit loads. Part 25 provides the same requirement without the
additional 1.33 factor.There is merit in considering the maximum
steering torque in combination with a ground reaction that is greater
than the static one, however there is insufficient justification for an
additional factor on the maximum steering torque. Therefore the rule
would be revised to include a 1.33 factor for the static ground
reaction. A related JAA proposal would remove the 1.33 factor from the
maximum steering torque in Sec. 25.499(e) of JAR-25, resulting in an
identical requirement. This proposal would result in an increase in the
level of safety provided by part 25.
Section 25.561(c) would be revised to be equivalent with
Sec. 25.561(c) of JAR-25. This would require the application of a 1.33
factor to the loads used to design the restraints of items of mass if
the failure of those items could injure occupants in an emergency
landing. This would also incorporate a provision that the 1.33 factor
applies only to items of mass that are frequently removed during normal
operation. This change would provide an increase in the level of safety
provided by part 25.
Regulatory Evaluation Summary
Preliminary Regulatory Evaluation, Initial Regulatory Flexibility
Determination, and Trade Impact Assessment
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) Would
generate benefits that justify its costs and is not a ``significant
regulatory action'' as defined in the Executive Order; (2) is not
significant as defined in the Department of Transportation's (DOT)
Regulatory Policies and Procedures; (3) would not have a significant
impact on a substantial number of small entities; and (4) would not
constitute a barrier to international trade. These analyses, available
in the docket, are summarized below.
[[Page 45001]]
Regulatory Evaluation Summary
Depending on airplane design, the proposed rule could result in
additional compliance costs for some manufacturers. If manufacturers
choose to design to and justify a VD-VC margin of 0.05 Mach,
there would be an increase in analysis costs of approximately $145,000
per certification. The proposed requirement in Sec. 25.473 to consider
structural flexibility in the analysis of landing loads and the
proposed increase in the factor on the maximum static reaction on the
nose gear vertical force in Sec. 25.499 could add compliance costs, but
the FAA estimates that these would be negligible.
The proposed rule would also result in cost savings. Proposed
revisions in the conditions in which unchecked pitch maneuvers are
investigated could reduce certification costs by as much as $10,000 per
certification. The FAA estimates that the proposed change in the speed
margin between VB and VC from a fixed margin to a margin
variable with altitude could result in substantial, though
unquantified, cost savings to some manufacturers. Manufacturers that
design small transport category airplanes with direct mechanical rudder
control systems could realize a savings as a result of the modification
in the rudder control force limit in proposed Sec. 25.351. The FAA
solicits information from manufacturers and other interested parties
concerning these and other benefits of the proposed rule.
The primary benefit of the proposed rule would be cost savings
associated with harmonization of part 25 with JAR-25. In order to sell
airplanes in a global marketplace, manufacturers usually certify their
products under part 25 and JAR-25. Harmonizing design load requirements
would outweigh any incremental costs of the proposal, resulting in a
net cost savings. These savings would be realized by U.S. manufacturers
that market airplanes in JAA countries as well as by manufacturers in
JAA countries that market airplanes in the United States.
The proposed change to Sec. 25.335(b)(2) in the minimum speed
margin for atmospheric conditions from 0.05 Mach and 0.07 Mach could
produce safety benefits. The increase in the margin between VD/
MD and VC/MC would be more conservative and would
standardize training across international lines. Crews could cross-
train and cross-fly and this standardization could enhance safety as
well as result in more efficient training.
The FAA solicits information from manufacturers and other
interested parties concerning these and other benefits of the proposed
rule.
Regulatory Flexibility Determination
The Regulatory Flexibility Act of 1980 (RFA) was enacted by
Congress to ensure that small entities are not unnecessarily and
disproportionally burdened by Federal regulations. The RFA requires
agencies to determine whether rules would have ``a significant economic
impact on a substantial number of small entities,'' and, in cases where
they would, to conduct a regulatory flexibility analysis. Based on FAA
Order 2100.14A, Regulatory Flexibility Criteria and Guidance, the FAA
has determined that the proposed revisions would not have a significant
economic impact on a substantial number of small entities because there
are no small manufacturers of transport category airplanes.
International Trade Impact Assessment
The proposed rule would not constitute a barrier to international
trade, including the export of U.S. airplanes to foreign markets and
the import of foreign airplanes into the United States. Because the
proposed rule would harmonize with the JAR, it would, in fact, lessen
restraints on trade.
Federalism Implications
The regulations proposed herein would not have substantial direct
effects on the states, on relationship between the national government
and the states, or on the distribution of power and responsibilities
among the various levels of government. Thus, in accordance with
Executive Order 12612, it is determined that this proposal does not
have sufficient federalism implications to warrant the preparation of a
Federalism Asssessment.
Conclusion
Because the proposed changes to the structural loads requirements
are not expected to result in any substantial economic costs, the FAA
has determined that this proposed regulation would not be significant
under Executive Order 12866. Because there has not been significant
public interest in this issue, FAA has determined that this action is
not significant under DOT Regulatory Policies and Procedures (44 FR
11034; February 25, 1979). In addition, since there are no small
entities affected by this rulemaking, the FAA certifies that the rule,
if promulgated, would not have a significant economic impact, positive
or negative, on a substantial number of small entities under the
criteria of the Regulatory Flexibility Act, since none would be
affected. A copy of the regulatory evaluation prepared for this project
may be examined in the Rules Docket or obtained from the person
identified under the caption FOR FURTHER INFORMATION CONTACT.
List of Subjects in 14 CFR Part 25
Air transportation, Aircraft, Aviation safety, Safety.
The Proposed Amendments
Accordingly, the Federal Aviation Administration (FAA) proposes to
amend 14 CFR part 25 of the Federal Aviation Regulations as follows:
PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
1. The authority citation for Part 25 continues to read as follows:
Authority: 49 U.S.C. App. 1347, 1348, 1354(a), 1357(d)(2), 1372,
1421 through 1430, 1432, 1442, 1443, 1472, 1510, 1522, 1652(e),
1655(c), 1657(f), 49 U.S.C. 106(g).
2. Section 25.331 is amended by revising the introductory text of
paragraph (c) and paragraph (c)(1) to read as follows:
Sec. 25.331 General.
* * * * *
(c) Pitch maneuver conditions. The conditions specified in
paragraphs (c) (1) and (2) of this section must be investigated. The
movement of the pitch control surfaces may be adjusted to take into
account limitations imposed by the maximum pilot effort specified by
Sec. 25.397(b), control system stops and any indirect effect imposed by
limitations in the output side of the control system (for example,
stalling torque or maximum rate obtainable by a power control system).
(1) Maximum pitch control displacement at VA. The airplane is
assumed to be flying in steady level flight (point A1,
Sec. 25.333(b)) and the cockpit pitch control is suddenly moved to
obtain extreme nose up pitching acceleration. In defining the tail
load, the response of the airplane must be taken into account. Airplane
loads that occur subsequent to the time when normal acceleration at the
c.g. exceeds the positive limit maneuvering load factor (at point
A2 Sec. 25.333(b)), or the resulting tailplane normal load reaches
its maximum, whichever occurs first, need not be considered.
* * * * *
3. Section 25.335 is amended by revising paragraphs (a)(2) and
(b)(2) to read as follows:
Sec. 25.335 Design airspeeds.
* * * * *
[[Page 45002]]
(a) * * *
(2) Except as provided in Sec. 25.335(d)(2), VC may not be
less than VB+1.32 UREF (with UREF as specified in
Sec. 25.341(a)(5)(i)). However VC need not exceed the maximum
speed in level flight at maximum continuous power for the corresponding
altitude.
(3) * * *
(b) * * *
(2) The minimum speed margin must be enough to provide for
atmospheric variations (such as horizontal gusts, and penetration of
jet streams and cold fronts) and for instrument errors and airframe
production variations. These factors may be considered on a probability
basis. The margin at altitude where MC is limited by
compressibility effects must not be less than 0.07M unless a lower
margin is determined using a rational analysis that includes the
effects of any automatic systems. In any case, the margin may not be
reduced to less than 0.05M.
* * * * *
4. Section 25.345 is amended by revising paragraph (d) to read as
follows:
Sec. 25.345 High lift devices.
* * * * *
(d) The airplane must be designed for a maneuvering load factor of
1.5g at the maximum take-off weight with the wing-flaps and similar
high lift devices in the landing configurations.
5. Section 25.351 is revised to read as follows:
Sec. 25.351 Yaw maneuver conditions.
The airplane must be designed for loads resulting from the yaw
maneuver conditions specified in paragraphs (a) through (d) of this
section at speeds from VMC to VD. Unbalanced aerodynamic
moments about the center of gravity must be reacted in a rational or
conservative manner considering the airplane inertia forces. In
computing the tail loads the yawing velocity may be assumed to be zero.
(a) With the airplane in unaccelerated flight at zero yaw, it is
assumed that the cockpit rudder control is suddenly displaced to
achieve the resulting rudder deflection, as limited by:
(1) The control system or control surface stops; or
(2) A limit pilot force of 300 pounds from VMC to VA and
200 pounds from VC/MC to VD/MD, with a linear
variation between VA and VC/MC.
(b) With the cockpit rudder control deflected so as always to
maintain the maximum rudder deflection available within the limitations
specified in paragraph (a) of this section, it is assumed that the
airplane yaws to the overwing sideslip angle.
(c) With the airplane yawed to the static equilibrium sideslip
angle, it is assumed that the cockpit rudder control is held so as to
achieve the maximum rudder deflection available within the limitations
specified in paragraph (a) of this section.
(d) With the airplane yawed to the static equilibrium sideslip
angle of paragraph (c) of this section, it is assumed that the cockpit
rudder control is suddenly returned to neutral.
6. Section 25.363 is amended by revising the title and paragraph
(a) to read as follows:
Sec. 25.363 Side load on engine and auxiliary power unit mounts.
(a) Each engine and auxiliary power unit mount and its supporting
structure must be designed for a limit load factor in a lateral
direction, for the side load on the engine and auxiliary power unit
mount, at least equal to the maximum load factor obtained in the yawing
conditions but not less than--
(1) 1.33; or
(2) One-third of the limit load factor for flight condition A as
prescribed in Sec. 25.333(b).
* * * * *
7. Section 25.371 is revised to read as follows:
Sec. 25.371 Gyroscopic loads.
The structure supporting any engine or auxiliary power unit must be
designed for the loads including the gyroscopic loads arising from the
conditions specified in Secs. 25.331, 25.341(a), 25.349, 25.351,
25.473, 25.479, and 25.481, with the engine or auxiliary power unit at
the maximum rpm appropriate to the condition. For the purposes of
compliance with this section, the pitch maneuver in Sec. 25.331(c)(1)
must be carried out until the positive limit maneuvering load factor
(point A2 in Sec. 25.333(b)) is reached.
8. Section 25.415 is amended by revising paragraph (a)(2) to read
as follows:
Sec. 25.415 Ground gust conditions.
(a) * * *
(1) * * *
(2) The control system stops nearest the surfaces, the control
system locks, and the parts of the systems (if any) between these stops
and locks and the control surface horns, must be designed for limit
hinge moments H, in foot pounds, obtained from the formula,
H=14.3 KcS,
where--
K=limit hinge moment factor for ground gusts derived in paragraph (b)
of this section.
c=mean chord of the control surface aft of the hinge line (ft);
S=area of the control surface aft of the hinge line (sq. ft);
* * * * *
9. Section 25.473 is revised to read as follows:
Sec. 25.473 Landing load conditions and assumptions.
(a) For the landing conditions specified in Secs. 25.479 to 25.485
the airplane is assumed to contact the ground--
(1) In the attitudes defined in Sec. 25.479 and Sec. 25.481;
(2) With a limit descent velocity of 10 fps at the design landing
weight (the maximum weight for landing conditions at maximum descent
velocity); and
(3) With a limit descent velocity of 6 fps at the design take-off
weight (the maximum weight for landing conditions at a reduced descent
velocity).
(4) The prescribed descent velocities may be modified if it is
shown that the airplane has design features that make it impossible to
develop these velocities.
(b) Airplane lift, not exceeding airplane weight, may be assumed
unless the presence of systems or procedures significantly affects the
lift.
(c) The method of analysis of airplane and landing gear loads must
take into account at least the following elements:
(1) Landing gear dynamic characteristics.
(2) Spin-up and springback.
(3) Rigid body response.
(4) Structural dynamic response of the airframe, if significant.
(d) The limit inertia load factors corresponding to the required
limit descent velocities must be validated by tests as defined in
Sec. 25.723(a).
(e) The coefficient of friction between the tires and the ground
may be established by considering the effects of skidding velocity and
tire pressure. However, this coefficient of friction need not be more
than 0.8.
10. Section 25.479 is revised to read as follows:
Sec. 25.479 Level landing conditions.
(a) In the level attitude, the airplane is assumed to contact the
ground at forward velocity components, ranging from VL1 to 1.25
VL2 parallel to the ground under the conditions prescribed in
Sec. 25.473 with--
(1) VL1 equal to VS0 (TAS) at the appropriate landing
weight and in standard sea level conditions; and
(2) VL2 equal to VS0 (TAS) at the appropriate landing
weight and
[[Page 45003]]
altitudes in a hot day temperature of 41 degrees F. above standard.
(3) The effects of increased contact speed must be investigated if
approval of downwind landings exceeding 10 knots is requested.
(b) For the level landing attitude for airplanes with tail wheels,
the conditions specified in this section must be investigated with the
airplane horizontal reference line horizontal in accordance with Figure
2 of Appendix A of this part.
(c) For the level landing attitude for airplanes with nose wheels,
shown in Figure 2 of Appendix A of this part, the conditions specified
in this section must be investigated assuming the following attitudes:
(1) An attitude in which the main wheels are assumed to contact the
ground with the nose wheel just clear of the ground; and
(2) If reasonably attainable at the specified descent and forward
velocities, an attitude in which the nose and main wheels are assumed
to contact the ground simultaneously.
(d) In addition to the loading conditions prescribed in paragraph
(a) of this section, but with maximum vertical ground reactions
calculated from paragraph (a), the following apply:
(1) The landing gear and directly affected attaching structure must
be designed for the maximum vertical ground reaction combined with an
aft acting drag component of not less than 25% of this maximum vertical
ground reaction.
(2) The most severe combination of loads that are likely to arise
during a lateral drift landing must be taken into account. In absence
of a more rational analysis of this condition, the following must be
investigated:
(i) A vertical load equal to 75% of the maximum ground reaction of
Sec. 25.473 must be considered in combination with a drag and side load
of 40% and 25% respectively of that vertical load.
(ii) The shock absorber and tire deflections must be assumed to be
75% of the deflection corresponding to the maximum ground reaction of
Sec. 25.25.473(a)(2). This load case need not be considered in
combination with flat tires.
(3) The combination of vertical and drag components is considered
to be acting at the wheel axle centerline.
11. Section 25.481 is amended by revising paragraph (a)
introductory text to read as follows:
Sec. 25.481 Tail down landing conditions.
(a) In the tail-down attitude, the airplane is assumed to contact
the ground at forward velocity components, ranging from VL1 to
VL2 parallel to the ground under the conditions prescribed in
Sec. 25.473 with--
* * * * *
12. Section 25.483 is amended by revising the title, introductory
text, and paragraph (a) to read as follows:
Sec. 25.483 One-gear landing conditions.
For the one-gear landing conditions, the airplane is assumed to be
in the level attitude and to contact the ground on one main landing
gear, in accordance with Figure 4 of Appendix A of this part. In this
attitude--
(a) The ground reactions must be the same as those obtained on that
side under Sec. 25.479(d)(1), and
* * * * *
13. Section 25.485 is amended by adding introductory text to read
as follows:
Sec. 25.485 Side load conditions.
In addition to Sec. 25.479(d)(2) the following conditions must be
considered:
* * * * *
14. Section 25.491 is revised to read as follows:
Sec. 25.491 Taxi, takeoff and landing roll.
Within the range of appropriate ground speeds and approved weights,
the airplane structure and landing gear are assumed to be subjected to
loads not less than those obtained when the aircraft is operating over
the roughest ground that may reasonably be expected in normal
operation.
15. Section 25.499 is amended by revising the heading and paragraph
(e) to read as follows:
Sec. 25.499 Nose-wheel yaw and steering.
* * * * *
(e) With the airplane at design ramp weight, and the nose gear in
any steerable position, the combined application of full normal
steering torque and vertical force equal to 1.33 times the maximum
static reaction on the nose gear must be considered in designing the
nose gear, its attaching structure, and the forward fuselage structure.
16. Section 25.561 is amended by revising paragraph (c) to read as
follows:
Sec. 25.561 General.
* * * * *
(c) For equipment, cargo in the passenger compartments and any
other large masses, the following apply:
(1) These items must be positioned so that if they break loose they
will be unlikely to
(i) Cause direct injury to occupants;
(ii) Penetrate fuel tanks or lines or cause fire or explosion
hazard by damage to adjacent systems; or
(iii) Nullify any of the escape facilities provided for use after
an emergency landing.
(2) When such positioning is not practical (e.g., fuselage mounted
engines or auxiliary power units) each such item of mass shall be
restrained under all loads up to those specified in paragraph (b)(3) of
this section. The local attachments for these items should be designed
to withstand 1.33 times the specified loads if these items are subject
to severe wear and tear through frequent removal (e.g., quick change
interior items).
* * * * *
Issued in Washington, D.C. on August 16, 1995.
Thomas E. McSweeny,
Director, Aircraft Certification Service.
[FR Doc. 95-21012 Filed 8-28-95; 8:45 am]
BILLING CODE 4910-13-M
