Revised Landing Gear Shock Absorption Test Requirements

SUMMARY: This document proposes to revise the landing gear shock

absorption test requirements for transport category airplanes by

incorporating changes developed in cooperation with the Joint Aviation

Authorities (JAA) of Europe and the U.S. and European aviation industry

through the Aviation Rulemaking Advisory Committee (ARAC). This action

is necessary because the increasing complexity of landing gear shock

absorption systems and the improvements in other requirements

concerning landing loads have rendered the current requirements

inconsistent and outdated. In addition, differences between the current

United States and European requirements impose unnecessary costs on

airplane manufacturers. These proposals are intended to update the

landing gear requirements to be consistent with other requirements, to

reflect modern technology, and to achieve common requirements and

language between the Federal Aviation Regulations and the European

Joint Aviation Requirements (JAR) without reducing the level of safety

provided by the regulations and industry practices.

DATES: Comments must be received on or before October 18, 1999.

ADDRESSES: Comments on this proposal may be mailed in duplicate to:

U.S. Department of Transportation, Dockets, Docket No. FAA-1999-5835,

400 Seventh Street SW., Room Plaza 401, Washington, D.C. 20590.

Comments may also be submitted electronically to the following address:

[email protected] Comments may be examined in Room Place 401 between

10 a.m. and 5 p.m., weekdays, except Federal holidays. 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/Cabin Safety

Branch, ANM-115, Transport Airplane Directorate, Aircraft Certification

Service, FAA, 1601 Lind Avenue, SW., Renton, WA 98055-4056; telephone

(425) 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

action are invited. Substantive comments should be accompanied by cost

estimates. Commenters should identify the regulatory docket or notice

number and submit comments in duplicate to the 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. Late filed comments will be considered to the

extent practicable. The proposals contained in this action may be

changed in light of comments received. All comments received will be

available in the 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. FAA-1999-5835.'' The

postcard will be date/time stamped and returned to the commenter.

Availability of NPRM

An electronic copy of this document may be downloaded using a modem

and suitable communications software from the FAA regulations section

of the Fedworld electronic bulletin board service (telephone: 703-321-

3339), the Government Printing Office's electronic bulletin board

service (telephone: 202-512-1661), or the FAA's Aviation Rulemaking

Advisory Committee Bulletin Board service (telephone: 800-322-2722 or

202-267-5948).

Internet users may reach the FAA's web page at http://www.faa.gov/

avr/arm/nprm.htm or the Government Printing Office's web page at http:/

/www.access.gpo.gov/nara for access to recently published rulemaking

documents.

Any person may obtain a copy of this document by submitting a

request to the Federal Aviation Administration, Office of Rulemaking,

ARM-1, 800 Independence Avenue SW., Washington, DC 20591; or by calling

(202) 267-9680. Communications must identify the docket or 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 airplanes that is administered by the Joint Aviation

Authorities (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 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.

The Aviation Rulemaking Advisory Committee (ARAC) was established

by the FAA on February 15, 1991, with the purpose of providing

information, advice, and recommendations to be considered in rulemaking

activities. By notice in the Federal Register (59 FR 30081, June 10,

1994), the FAA assigned several new tasks to an ARAC working group of

industry and government structural loads specialists from Europe, the

United States, and Canada. Task 6 of the working group charter

concerned the shock absorption test requirements for landing gear. The

ARAC working group has completed its work for this task and the ARAC

has made recommendations to the FAA by letter dated October 29, 1997.

Although the requirements for landing gear shock absorption tests

are essentially the same between the Federal Aviation Regulations and

JAR, the requirements do not address the capabilities of modern

technology and

[[Page 32979]]

do not take into account other related changes in the requirements for

landing gear load conditions that have already been incorporated into

other sections of the Federal Aviation Regulations. When the landing

loads requirements for transport airplanes were originally developed,

they required the landing load factors to be determined and applied to

the airplane. The airplane was treated as a rigid body and the landing

loads were applied to this rigid representation of the airplane for the

purpose of structural analysis. For the early landing gear systems,

analysis alone was considered sufficient for determining the landing

load factor that would be applied to the rigid airplane. It was only

necessary to determine the landing load factor (by analysis or tests)

and this load factor would then be used to design and substantiate the

airplane for the landing load conditions.

The development of more complex landing gear systems, for which

analysis alone was unreliable, led to the adoption of a requirement to

verify the landing load factor by actual shock absorption tests. This

requirement was added to the Civil Air Regulations (CAR) part 4b, which

was the predecessor to part 25. These shock absorption tests were

allowed by Sec. 4b.200 of the CAR to be free drop tests in which the

gear alone, could be dropped in free fall to impact the ground. In

these tests, mass is added to represent the proportion of the airplane

weight on the landing gear unit, and the mass may be reduced to account

for the effects of airplane lift acting during the landing impact.

Later, the corresponding requirement in Sec. 25.723(a), was modified to

allow the substantiation of some changes to the landing gear shock

absorption systems by analysis alone without verification by tests.

Part 25 currently requires the landing loads to be determined by

accounting for the dynamic flexible airplane. In addition, the landing

gear shock absorption systems have become even more sophisticated. At

the same time, the ability to develop highly sophisticated computer

models of landing gear and airplane structures has also improved. In

order to determine the airplane loads from the landing load conditions,

it is no longer sufficient to determine just the load factor from a

drop test of a landing gear unit. A comprehensive analysis of the

combined dynamic systems for the landing gear and airplane are

essential in order to determine the structural design loads for the

airplane. In developing this dynamic model, it is necessary to provide

an accurate representation of all the landing gear dynamic

characteristics. This includes the energy absorption characteristics

and the time histories of force and displacement during a landing

impact. The current Secs. 25.473(d) and 25.723(a) for shock absorption

tests require just the determination of the limit landing load factor

from the drop test.

Discussion

The proposed revisions to Sec. Sec. 25.473(d) and 25.723(a) would

provide for the new objective of the landing gear energy absorption

tests which would be to validate the landing gear dynamic

characteristics rather than to directly determine landing gear load

factors. These revisions would require that these characteristics be

substantiated over the range of landing conditions and airplane

configurations expected in service. The manufacturer would be expected

to substantiate the landing gear dynamic characteristics over the full

range of weight conditions and configurations. As a minimum, the energy

absorption characteristics would be confirmed by an energy absorption

test at the weight condition for landing (maximum takeoff weight or

maximum landing weight) which provides the maximum impact energy. This

is in contrast to the current Sec. Sec. 25.473(d) and 25.723(a) which

specifically require energy absorption tests at both the maximum

landing weight condition and the maximum takeoff weight condition. The

proposed rule would continue to provide for the substantiation of minor

changes by analyses. To provide guidance in complying with the new

proposed rule, a new advisory circular, AC 25.723-1, Shock Absorption

Tests, is proposed.

The proposals for the revised Sec. Sec. 25.473(d) and 25.723(a)

take into account the potential for sophisticated computer simulations

that accurately represent the dynamic characteristics. These are also

consistent with improvements in the landing load requirements that

necessitate an accurate representation of the landing gear shock

absorption characteristics. These proposals also provide more

flexibility for the airplane manufacturer to determine the range of

conditions and configurations over which to validate the analytical

model for the landing conditions. The extent to which this analytical

model could be extrapolated to include future design changes would

depend on the range of conditions and configurations originally

selected by the manufacturer for validation of the model.

The current Sec. Sec. 25.725 and 25.727 are proposed to be deleted

as regulatory requirements and would be set forth in the new proposed

AC 25.723-1. These criteria would be modified to reflect the advisory

nature of the material as well as the revised objective of determining

landing gear dynamic characteristics instead of landing gear limit

inertia load factors. For the most part, these rules currently provide

acceptable means of conducting energy absorption tests by means of a

drop test. Section 25.725 provides an acceptable means of conducting a

limit drop test for compliance with Sec. 25.723(a), and Sec. 25.727

provides an acceptable means of conducting a reserve energy drop test

in compliance with Sec. 25.723(b). Most of the guidance is limited to a

``free'' drop test in which a reduced effective weight is used to

represent lift during the landing impact. The only item in these two

sections that is considered to be regulatory in nature is the current

Sec. 25.725(c) concerning the attitude of the landing gear and the

representation of drag loads during the tests. Therefore this paragraph

has been modified to apply to all types of landing gear energy

absorption tests (not just drop tests) and it is now set forth in

Sec. 25.723(a)(2) of the proposed rule. It is expected that these

revisions will have no effect on the level of safety provided by the

requirement.

Paperwork Reduction Act

In accordance with the Paperwork Reduction Act of 1995 (44 U.S.C.

3507(d)), there are no requirements for information collection

associated with this proposed rule.

International Compatibility

The FAA has reviewed corresponding International Civil Aviation

Organization international standards and recommended practices and

Joint Aviation Authorities regulations, where they exist, and has

identified no differences in these proposed amendments and the foreign

regulations.

Regulatory Evaluation Summary

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 effect

of regulatory changes on international trade. In conducting these

analyses, the FAA has determined that this proposed

[[Page 32980]]

rule is not ``a significant regulatory action'' under section 3(f) of

Executive Order 12866 and, therefore, is not subject to review by the

Office of Management and Budget. This proposed rule is not considered

significant under the regulatory policies and procedures of the

Department of Transportation (44 FR 11034, February 26, 1979). This

proposed rule would not have a significant impact on a substantial

number of small entities and would not constitute a barrier to

international trade. The FAA invites the public to provide comments and

supporting data on the assumptions made in this evaluation. All

comments received will be considered in the final regulatory

evaluation.

The proposed requirements, applicable to future type certificated

transport category airplanes, would result in two regulatory changes:

(1) Utilizing landing gear energy absorption tests to validate the

landing gear dynamic characteristics rather than the limit load factor

value, and (2) confirming energy absorption characteristics by

requiring tests at either the maximum landing weight or maximum takeoff

weight condition, whichever provides the maximum landing impact energy.

This is in contrast to current requirements which require tests at both

weight conditions.

The test results would be used to develop the analytical modeling

of the landing gear dynamic characteristics. These regulatory changes

would not result in any physical change in the way landing gears are

tested: the attitude of the gear being usually simulated directly by

orienting the gear on the rig and drag loads being applied by spinning

the wheel up to the ground speed. Therefore, it would not impose

additional costs on manufacturers. This was confirmed by two

manufacturers.

Significant cost savings may result from not having to test both at

maximum landing weight and maximum takeoff weight, but instead,

conducting shock absorption tests only for the conditions associated

with maximum energy. One manufacturer estimates that these tests would

result in 15 fewer test conditions per airplane certification. At a

cost of $5,000 per condition, the total cost savings would reach

$75,000 per airplane certification. Another manufacturer estimates a

cost savings of approximately $190,000 for a ten-year period.

Additionally, by harmonizing the standards of the Federal Aviation

Regulations and JAR, the proposed rule would yield cost savings by

eliminating duplicate certification activities.

Based on the finding of regulatory cost-savings, coupled with the

cost-savings realizable from harmonization, and the expectation that

these revisions will have no effect on the level of safety provided by

the test requirements, the FAA has determined that the proposed rule

would be cost-beneficial.

Initial Regulatory Flexibility Determination

The Regulatory Flexibility Act of 1980 establishes ``as a principle

of regulatory issuance that agencies shall endeavor, consistent with

the objective of the rule and of applicable statutes, to fit regulatory

and informational requirements to the scale of the business,

organization, and governmental jurisdictions subject to regulation.''

To achieve that principal, the Act requires agencies to solicit and

consider flexible regulatory proposals and to explain the rationale for

their actions. The Act covers a wide range of small entities, including

small businesses, not-for-profit organizations and small governmental

jurisdictions.

Agencies must perform a review to determine whether a proposed or

final rule will have a significant economic impact on a substantial

number of small entities. If the determination is that it will, the

agency must prepare a regulatory flexibility analysis (RFA) as

described in the Act. However, if an agency determines that a proposed

or final rule is not expected to have a significant economic impact on

a substantial number of small entities, section 605(b) of the 1980 act

provides that the head of the agency may so certify and an RFA is not

required. The certification must include a statement providing the

factual basis for this determination, and the reasoning should be

clear.

The proposed rule would affect manufacturers of transport category

airplanes produced under future new airplane type certifications. For

manufacturers, a small entity has 1,500 or fewer employees. Since no

part 25 airplane manufacturer has 1,500 or fewer employees, FAA

certifies that the proposed rule will not have a significant economic

impact on a substantial number of small entities.

International Trade Impact Statement

The provisions of this proposed rule would have no adverse impact

on trade for both U.S. firms doing business in foreign countries and

foreign firms doing business in the United States. By making U.S.

landing gear test requirements conform with JAR requirements,

international trade in aircraft would be enhanced by eliminating

redundant testing costs for part 25 airplane manufacturers, possibly

resulting in some cost savings for users of aircraft.

Federalism Implications

The regulations proposed herein would not have substantial direct

effects on the states, on the relationship between the national

government and the states, or on the distribution of power and

responsibilities among the various levels of government. 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 assessment.

Unfunded Mandates Reform Act

Title II of the Unfunded Mandates Reform Act of 1995 (the Act),

codified in 2 U.S.C. 1501-1571, requires each Federal agency, to the

extent permitted by law, to prepare a written assessment of the effects

of any Federal mandate in a proposed or final agency rule that may

result in the expenditure by State, local, and tribal governments, in

the aggregate, or by the private sector, of $100 million or more

(adjusted annually for inflation) in any one year. Section 204(a) of

the Act, 2 U.S.C. 1534(a), requires the Federal agency to develop an

effective process to permit timely input by elected officers (or their

designees) of State, local, and tribal governments on a proposed

``significant intergovernmental mandate.'' A ``significant

intergovernmental mandate'' under the Act is any provision in a Federal

agency regulation that would impose an enforceable duty upon State,

local, and tribal governments, in the aggregate, of $100 million

(adjusted annually for inflation) in any one year. Section 203 of the

Act, 2 U.S.C. 1533, which supplements section 204(a), provides that

before establishing any regulatory requirements that might

significantly or uniquely affect small governments, the agency shall

have developed a plan that, among other things, provides for notice to

potentially affected small governments, if any, and for a meaningful

and timely opportunity to provide input in the development of

regulatory proposals.

This proposed rule does not contain a Federal intergovernmental or

private sector mandate that exceeds $100 million a year.

Regulations Affecting Interstate Aviation in Alaska

Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat.

3213) requires the Administrator, when

[[Page 32981]]

modifying regulations in Title 14 of the CFR in a manner affecting

interstate aviation in Alaska, to consider the extent to which Alaska

is not served by transportation modes other than aviation, and to

establish such regulatory distinctions as he or she considers

appropriate. Because this proposed rule would apply to the

certification of future designs of transport category airplanes and

their subsequent operation, it could, if adopted, affect interstate

aviation in Alaska. The FAA therefore specifically requests comments on

whether there is justification for applying the proposed rule

differently in interstate operations in Alaska.

Environmental Analysis

Federal Aviation Administration Order 1050.1D defines FAA actions

that may be categorically excluded from preparation of a National

Environmental Policy Act (NEPA) environmental assessment or

environmental impact statement. In accordance with FAA Order 1050.1D,

appendix 4, paragraph 4(j), this rulemaking, which if implemented may

cause a significant impact on the human environment, qualifies for a

categorical exclusion.

Energy Impact

The energy impact of the proposed rule has been assessed in

accordance with the Energy Policy and Conservation Act (EPCA) and

Public Law 94-163, as amended (42 U.S.C. 6362). It has been determined

that it is not a major regulatory action under the provisions of the

EPCA.

List of Subjects 14 CFR Part 25

Aircraft, Aviation safety, Reporting and recordkeeping

requirements.

The Proposed Amendments

In consideration of the foregoing, the Federal Aviation

Administration proposes to amend part 25 of Title 14, Code of Federal

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. 106(g), 40113, 44701, 44702 and 44704.

2. Section 25.473 is amended by revising paragraph (d) to read as

follows:

Sec. 25.473 Landing load conditions and assumptions.

* * * * *

(d) The landing gear dynamic characteristics must be validated by

tests as defined in Sec. 25.723(a).

* * * * *

3. Section 25.723 is amended by revising paragraph (a) to read as

follows:

Sec. 25.723 Shock absorption tests.

(a) Except as provided in paragraph (a)(3) of this section, the

landing gear dynamic characteristics used for design must be validated

by energy absorption tests. The dynamic characteristics must be

substantiated for the range of landing conditions, airplane

configurations, and service variations expected in operation.

(1) The configurations subjected to energy absorption tests must

include at least the maximum landing weight or the maximum takeoff

weight, whichever produces the greater value of landing impact energy.

(2) The test attitude of the landing gear unit and the application

of appropriate drag loads during the test must simulate the airplane

landing conditions in a manner consistent with the development of

rational or conservative limit loads.

(3) Changes in previously approved design weights and minor changes

in design may be substantiated by analyses based on previous tests

conducted on the same basic landing gear system that has similar energy

absorption characteristics.

* * * * *

Sec. 25.725 [Removed and Reserved]

4. Remove and reserve Sec. 25.725.

Sec. 25.727 [Removed and Reserved]

5. Remove and reserve Sec. 25.727.

* * * * *

Issued in Washington D.C. on June 10, 1999.

Frank Paskiewicz,

Acting Director, Aircraft Certification Service.

[FR Doc. 99-15381 Filed 6-17-99; 8:45 am]

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