[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]]

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Part IV





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



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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.

-----------------------------------------------------------------------

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