Revised Structural Loads Requirements for Transport Category Airplanes

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