Revision of Braking Systems Airworthiness Standards To Harmonize With European Airworthiness Standards for Transport Category Airplanes

SUMMARY: The Federal Aviation Administration proposes to revise the

airworthiness standards for transport category airplanes to harmonize

braking systems design and test requirements with standards proposed

for the European Joint Aviation Requirements (JAR). These proposals

were 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), and are intended to

benefit the public interest by standardizing certain requirements,

concepts, and procedures contained in the airworthiness standards

without reducing, but potentially enhancing, the current level of

safety.

DATES: Comments must be received on or before November 8, 1999.

ADDRESSES: Comments on this document should be mailed or delivered, in

duplicate, to U.S. Department of Transportation Dockets, Docket No.

FAA-1999-6063, 400 Seventh Street SW., Room Plaza 401, Washington DC

20590. Comments may also be sent electronically to the following

Internet address: [email protected] Comments may be filed and/or

examined in Room Plaza 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),

Federal Aviation Administration, Northwest Mountain Region, 1601 Lind

Avenue SW., Renton, WA 98055-4056. Comments in the information docket

may be examined between 7:30 a.m. and 4:00 p.m. weekdays, except

Federal holidays.

FOR FURTHER INFORMATION CONTACT: Mahinder K. Wahi, FAA, Propulsion/

Mechanical Systems/Cabin Safety Branch, ANM-112, Transport Airplane

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

(425) 227-2142; facsimile (425) 227-1320.

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 the environmental, energy, federalism,

or economic impact that might result from adopting the proposals in

this notice are also invited. Substantive comments should be

accompanied by cost estimates. Commenters must identify the regulatory

docket or notice number and submit comments in duplicate to the Docket

address specified above.

All comments received, as well as a report summarizing each

substantive public contact with FAA personnel concerning this

rulemaking, will be filed in the docket. The Docket is available for

public inspection before and after the comment closing date.

All comments received on or before the closing date will be

considered by the Administrator before taking action on this proposed

rulemaking. Comments filed late will be considered to the extent

practicable. The proposals in this notice may be changed in light of

the comments received.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this notice must include with those comments a

pre-addressed, stamped postcard on which the following statement is

made: ``Comments to Docket No. FAA-1999-6063.'' The postcard will be

date stamped and mailed to the commenter.

Availability of the 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/nprm.htm or the Government Printing Office's webpage at

http://www.access.gpo.gov/nara for access to recently published

rulemaking documents.

Any person may obtain a copy of this NPRM 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 notice number of docket

number of this NPRM.

Persons interested in being placed on the mailing list for future

NPRM's should request from the above office a copy of Advisory Circular

No. 11-2A, Notice of Proposed Rulemaking Distribution System, which

describes the application procedure.

Background

The airworthiness standards for transport category airplanes are

contained in 14 CFR part 25. Manufacturers of transport category

airplanes must show that each airplane they produce of a different type

design complies with the relevant standards of part 25. These standards

apply to airplanes manufactured within the U.S. for use by U.S.-

registered operators and to airplanes manufactured in other countries

and imported under a bilateral airworthiness agreement.

In Europe, the Joint Aviation Requirements (JAR) were developed by

the Joint Aviation Authorities (JAA) to provide a common set of

airworthiness standards for use within the Europe aviation community.

The airworthiness standards for European type certification of

transport category airplanes, JAR-25, are based on part 25 of Title 14.

Airplanes certificated to the JAR-25 standards, including airplanes

manufactured in the U.S. for export to Europe, receive type

certificates that are accepted by the aircraft certification

authorities of 23 European countries.

Although part 25 and JAR-25 are very similar, they are not

identical. Differences between the FAR and the JAR can result in

substantial additional costs when airplanes are type certificated to

both standards. These additional costs, however, frequently do not

bring about an increase in safety. For example, part 25 and JAR-25 may

use different means to accomplish the same safety intent. In this case,

the manufacturer is usually burdened with meeting both requirements,

although the level of safety is not increased correspondingly.

Recognizing that a common set of standards would not only economically

benefit the aviation industry, but would also maintain the necessary

high level of safety, the FAA and JAA consider harmonization to be a

high priority.

In 1988, the FAA, in cooperation with the JAA and other

organizations representing the American and European aerospace

industries, began a process to harmonize the airworthiness requirements

of the United States and

[[Page 43571]]

the airworthiness requirements of Europe, especially in the areas of

Flight Test and Structures.

The Aviation Rulemaking Advisory Committee

The Aviation Rulemaking Advisory Committee (ARAC) was formally

established by the FAA on January 22, 1991 (56 FR 2190) to provide

advice and recommendations concerning the full range of the FAA's

safety-related rulemaking activity. This advice was sought to develop

better rules in less overall time using fewer FAA resources than are

currently needed. The committee provides the opportunity for the FAA to

obtain firsthand information and insight from interested parties

regarding proposed new rules or revisions of existing rules.

There are 64 member organizations on the committee, representing a

wide range of interests within the aviation community. Meetings of the

committee are open to the public, except as authorized by section 10(d)

of the Federal Advisory Committee Act.

The ARAC establishes working groups to develop proposals to

recommend to the FAA for resolving specific issues. Tasks assigned to

working groups are published in the Federal Register. Although working

group meetings are not generally open to the public, all interested

parties are invited to participate as working group members. Working

groups report directly to the ARAC, and the ARAC must accept a working

group proposal before that proposal can be presented to the FAA as an

advisory committee recommendation.

The activities of the ARAC will not, however, circumvent the public

rulemaking procedures. After an ARAC recommendation is received and

found acceptable by the FAA, the agency proceeds with the normal public

rulemaking procedures. Any ARAC participation in a rulemaking package

will be fully disclosed in the public docket.

Starting in 1992, the FAA harmonization effort for various systems

related airworthiness requirements was undertaken by the ARAC. A

working group of industry and government braking systems specialists of

Europe, the United States, and Canada was chartered by notice in the

Federal Register (59 FR 30080, June 10, 1994). The working group was

tasked to develop a harmonized standard, such as a Technical Standard

Order (TSO), for approval of wheels and brakes to be installed on

transport category airplanes and to develop a draft notice of proposed

rulemaking (NPRM), with supporting economic and other required

analyses, and/or any other related guidance material or collateral

documents, such as advisory circulars, concerning new or revised

requirements and the associated test conditions for wheels, brakes and

braking systems, installed in transport category airplanes (Sec. 25.731

and 25.735). The JAA is to develop a similar proposal to amend JAR-25,

as necessary, to achieve harmonization.

The rulemaking proposal contained in this notice is based on a

recommendation developed by the Braking Systems Harmonization Working

Group, and presented to the FAA by the ARAC as a recommendation.

General Discussion of the Proposals

The FAA proposes to amend 14 CFR 25.731 and 25.735 to harmonize

these sections with JAR-25. The JAA intends to publish a Notice of

Proposed Amendment (NPA), also developed by the Braking Systems

Harmonization Working Group, to revise JAR-25 as necessary to ensure

harmonization in those areas for which the proposed amendments differ

from the current JAR-25, Change 14. When published, the NPA will be

placed in the docket for this rulemaking.

Generally, the FAA proposes to: (1) add appropriate existing JAR

requirements to achieve harmonization; (2) move some of the existing

regulatory text, considered to be of an advisory nature, to an advisory

circular; (3) add regulations addressing automatic brake systems, brake

wear indicators, pressure release devices, and system compatibility;

and (4) consolidate and/or separate requirement subparagraphs for

clarity.

A new proposed Advisory Circular (AC) 25.735-1X, Brakes and Braking

Systems Certification Tests and Analysis, has been developed by the

ARAC Harmonization Working Group to ensure consistent application of

these proposed revised standards. Public comments concerning AC 25.735-

1X are invited by separate notice published elsewhere in this issue of

the Federal Register. The JAA intends to publish an Advisory Material

Joint (AMJ), also developed by the Harmonization Working Group, to

accompany its NPA. The proposed AC and the proposed AMJ contain

harmonized advisory information.

A new proposed TSO-C135 has also been developed by the

Harmonization Working Group as a harmonized standard for approval of

transport airplane wheels and wheel and brake assemblies to replace

applicable parts of the existing TSO-C26c, Aircraft Wheels and Wheel-

Brakes Assemblies, dated May 18, 1984. Pubic comments concerning TSO-

C135 are invited by separate notice published elsewhere in this issue

of the Federal Register. The JAA intends to adopt TSO-C135 as Joint

Technical Standard Order (JTSO)-C135 and publish it to accompany their

NPA.

Section by Section Discussion of the Proposals

Proposal 1. The FAA proposes to revise the current heading of

Sec. 25.735, ``Brakes,'' to read ``Sec. 25.735 Brakes and braking

systems.''

Discussion: This section covers not only the brakes and their

performance requirements and safety considerations, but also provides

requirements for the systems and equipment associated with the brakes.

As examples, the proposed additional paragraph (b)(2) refers to the

brake hydraulic system and the hydraulic fluid supplying the brakes,

and the proposed paragraph (e) refers to the antiskid system. The

proposed change is of an editorial nature only, and consequently would

have no impact on the current level of safety.

Proposal 2. The FAA proposes to add a heading to and revise the

text of Sec. 25.735(a) to read, ``(a) Approval. Each assembly

consisting of a wheel(s) and brake(s) must be approved.''

Discussion: The current Sec. 25.735(a), which states that each

brake must be approved, is considered incomplete. Although a wheel not

associated with a brake (non-braked) may be approved on its own per the

applicable TSO, a brake approval is always considered in combination

with its associated wheel(s) (i.e., for a combined wheel(s) and

brake(s) assembly). The proposed change is of an editorial nature only

and therefore would have no impact on the current level of safety.

Applicable advisory information would be included in proposed AC

25.735-1X.

Proposal 3. The FAA proposes to add the heading ``Brake system

capability'' to Sec. 25.735(b), to separate and revise the current text

of the first sentence of Sec. 25.735(b) into Secs. 25.735(b) and

(b)(1), and to delete the current text of the entire second sentence to

read:

``(b) Brake system capability. The brake system, associated systems

and components must be designed and constructed so that: (1) if any

electrical, pneumatic, hydraulic or mechanical connecting or

transmitting element fails, or if any single source of hydraulic or

other brake operating energy supply is lost, it is possible to bring

the airplane to rest with a braked roll stopping distance of not more

than two times that

[[Page 43572]]

obtained in determining the landing distance as prescribed in

Sec. 25.125.''

Discussion: The current text of the first sentence of

Sec. 25.735(b) reads, ``The brake systems and associated systems must

be designed and constructed so that if any electrical, pneumatic,

hydraulic, or mechanical connecting or transmitting element (excluding

the operating pedal or handle) fails, or if any single source of

hydraulic or other brake operating energy supply is lost, it is

possible to bring the airplane to rest under conditions specified in

Sec. 25.125 with a mean deceleration during the landing roll of at

least 50 percent of that obtained in determining the landing distance

as prescribed in that section.''

Under this proposal, the term ``components'' would be added to the

terms ``brake system and associated systems'' in the first sentence to

make it more comprehensive. The parenthetical phrase ``(excluding the

operating pedal or handle)'' would be deleted because no justification

could be found for such an exclusion. The words ``braked roll stopping

distance'' would be inserted in place of ``landing roll'' to clarify

that the requirement refers only to the distance covered while the

brakes are applied. The change in concept from at least 50 percent mean

deceleration to not more than two times the landing distance is

intended to eliminate any possible confusion between ``mean'' and

``average'' deceleration, and to state the requirement more clearly in

terms of its real intent. The other changes in text are editorial and

are made for clarity.

The current second sentence reads ``subcomponents within the brake

assembly, such as brake drum, shoes, and actuators (or their

equivalents), shall be considered as connecting or transmitting

elements, unless it is shown that leakage of hydraulic fluid resulting

from failure of the sealing elements in these subcomponents within the

brake assembly would not reduce the braking effectiveness below that

specified in this paragraph.'' The current second sentence would be

removed and, due to its advisory content, included as guidance material

in proposed AC 25.735-1X.

The proposed changes are clarifications of current regulations and

the associated terminology and therefore would have no impact on the

current level of safety. Applicable advisory information would be

included in proposed AC 25.735-1X.

Proposal 4. The FAA proposes to add a new Sec. 25.735(b)(2) that

would contain the intent and content of the ACJ 25.735(b) of JAR-25

regarding protection against fire resulting from hydraulic fluid

leakage, spillage, or spraying on hot brakes. The proposal would state

that, ``(2) Fluid lost from a brake hydraulic system, following a

failure in, or in the vicinity of, the brakes, is insufficient to cause

or support a hazardous fire on the ground or in flight.''

Discussion: Although the proposed requirement was previously

included in ACJ 25.735(b) as acceptable means of compliance and

interpretative material, it is now thought more appropriate that these

practices should be considered as requirements as they have generally

been treated as such in the past by both airplane manufacturers and

regulatory authorities. The current level of safety would not be

affected by this proposed change as it would adopt an existing industry

practice. Applicable advisory material would be included in proposed AC

25.735-1X.

Proposal 5. The FAA proposes to add the heading ``Brake controls''

to Sec. 25.735(c), and to separate and revise the current text of

Sec. 25.735(c) into Secs. 25.735(c) and (c)(1) to read: ``(c) Brake

Controls. The brake controls must be designed and constructed so that:

(1) Excessive control force is not required for their operation.''

Discussion: The current text reads, ``Brake controls may not

require excessive control force in their operation.'' The proposed

changes are clarifications of current regulations and the associated

terminology and therefore the current level of safety would not be

impacted. Applicable advisory material would be included in proposed AC

25.735-1X.

Proposal 6. The FAA proposes to add a new Sec. 25.735(c)(2) to

read: ``(2) If an automatic braking system is installed, means are

provided to (i) arm and disarm the system, and (ii) allow the pilot(s)

to override the system by use of manual braking.''

Discussion: The intent and content of the proposed changes have

generally been adopted in the design of current automatic braking

systems and are currently included in FAA Order 8110.8, ``Engineering

Flight Test Guide for Transport Category Airplanes,'' as interpretative

and acceptable means of compliance. Consequently, both the airplane

manufacturers and the regulatory authorities have generally considered

them as standard practices; therefore, they would not impact the

current level of safety. Applicable advisory material would be included

in proposed AC 25.735-1X.

Proposal 7. The FAA proposes to amend Sec. 25.735(d) by adding the

heading, ``Parking brake,'' and by modifying the current text from,

``The airplane must have a parking control that, when set by the pilot,

will without further attention, prevent the airplane from rolling on a

paved, level runway with takeoff power on the critical engine.'' to

``(d) Parking brake. The airplane must have a parking brake control

that, when selected on, will, without further attention, prevent the

airplane from rolling on a dry and level paved runway when the most

adverse combination of maximum thrust on one engine and up to maximum

ground idle thrust on any, or all, other engine(s) is applied. The

control must be suitably located or be adequately protected to prevent

inadvertent operation. There must be indication in the cockpit when the

parking brake is not fully released.''

Discussion: Introduction of the word ``brake'' before ``control''

clarifies that the paragraph refers to the means provided to the

flightcrew for the application of the wheel brakes in the airplane

parking mode. By revising the text, as proposed, the requirements would

be enhanced to cover not only the case of a single engine takeoff

thrust check with all other engines stopped, but would also cover an

equally if not more probable case where any or all other engines are

operating and producing up to a maximum ground idle thrust. The

proposal also clarifies the extent of the takeoff thrust to be

considered for the ``critical'' engine as the maximum that can be

achieved, and by implication also requires the relevant thrust cases

for remaining engine(s) according to the environmental circumstances

that are dictated for the achievement of the maximum takeoff thrust on

the critical engine. The word ``dry'' is added solely for clarification

of the current understanding of this requirement.

The requirement for suitable location or protection against

inadvertent operation of the parking brake control is derived from the

current ACJ 25.735(d) of JAR-25 and is introduced because it is

believed that such considerations should be regarded as requirements,

and have generally been treated as such in the past by both airplane

manufacturers and regulatory authorities. The additional requirement

for cockpit indication when the parking brake is ``not fully released''

is to caution the pilot against a takeoff with the parking brake set.

The proposed changes potentially enhance the current level of safety by

clarifying intent and addressing come critical cases. Applicable

advisory material would be included in proposed AC 25.735-1X.

Proposal 8. The FAA proposes to add the heading ``Antiskid system''

to Sec. 25.735(e), to delete the current text

[[Page 43573]]

``no single probable malfunction will result in a hazardous loss of

braking ability or directional control of the airplane'' as being

superfluous, and in order to facilitate the introduction of the new

proposed Sec. 25.735(e)(1) and (e)(2) under proposals 9 and 10

respectively, revise the remaining current text to read:

``(e) Antiskid system. If an antiskid system is installed:''

Discussion: The current Sec. 25.735(e9 reads: ``If antiskid devices

are installed, the devices and associated systems must be designed so

that no single probable malfunction will result in hazardous loss of

braking ability or directional control of the airplane.'' The reference

to antiskid devices and associated systems would be changed to

``antiskid system,'' this being more appropriate to the paragraph's

intent. The term ``probable'' was incompatible with the terminology of

Sec. 25.1309 because a ``probable'' malfunction cannot be associated

with either major or hazardous effects and, if used in the

``Sec. 25.1309'' sense, could lead to a requirement that could be seen

as less severe than Sec. 25.1309 for that specific failure condition,

with no obvious technical/state of the art reasons. It appears that the

terminology (probable and hazardous) used was probably not

``Sec. 25.1309 related'' when the requirement was first introduced.

Rather than trying to define the words, it is considered that the

requirement is adequately covered by Sec. 25.1309 and the current

Sec. 25.735(e) is superfluous. The proposed changes are of a clarifying

and an editorial nature only and therefore would have no impact on the

current level of safety. Appropriate advisory material would be

included in proposed AC 25.735-1X.

Proposal 9. The FAA proposes to add a new Sec. 25.735(e)(1) to

read.

``(1) It must operate satisfactory over the range of expected

runway conditions, without external adjustment.''

Discussion: The intent and content of the proposed changes are

currently included in FAA Order 8110.8, ``Engineering Flight Test Guide

for Transport Category Airplanes,'' as interpretative material and

acceptable means of compliance and are deemed appropriate to be adopted

as requirements. Both the airplane manufacturers and the regulatory

authorities have, in the past, considered them as standard practices;

therefore, they would not impact the current level of safety.

Applicable advisory material would be included in proposed AC 25.735-

1X.

Proposal 10. The FAA proposes to add a new Sec. 25.735(e)(2) to

read: ``(2) It must, at all times, have priority over the automatic

braking system, if installed.''

Discussion: The intent and content of the proposed change is

currently included in FAA Order 8110.8, ``Engineering Flight Test Guide

for Transport Category Airplanes,'' as interpretative material and

acceptable means of compliance and is deemed appropriate to be adopted

as a requirement. Both the airplane manufacturers and the regulatory

authorities have, in the past, considered it as a standard practice;

therefore, it would not impact the current level of safety. Applicable

advisory material would be included in proposed AC 25.735-1X.

Proposal 11. The FAA proposes to amend Sec. 25.735(f) by adding the

heading ``Kinetic energy capacity,'' by consolidating the requirements

of current paragraphs (f) and (h), by adding similar requirements for a

high energy landing condition, by removing paragraphs (f)(1) and (2),

and paragraphs (h)(1) and (2), and by revising the text to read:

``(f) Kinetic energy capacity. The design landing stop, the maximum

kinetic energy accelerate-stop, and the most severe landing stop brake

kinetic energy absorption requirements of each wheel and brake assembly

must be determined. It must be substantiated by dynamometer testing

that, at the declared fully worn limit(s) of the brake heat sink, the

wheel and brake assemblies are capable of absorbing not less than these

levels of kinetic energy. Energy absorption rates defined by the

airplane manufacturer must be achieved. These rates must be equivalent

to mean decelerations not less than 10 fps2 [feet per

second] for the design landing stop and 6 fps2 for the

maximum kinetic energy accelerate stop. The most severe landing stop

need not be considered for extremely improbable failure conditions or

if the maximum kinetic energy accelerate-stop energy is more severe.

Design landing stop is an operational landing stop at maximum landing

weight. Maximum kinetic energy accelerate-stop is a rejected takeoff

for the most critical combination of airplane takeoff weight and speed.

Most severe landing stop is a stop at the most critical combination of

airplane landing weight and speed.

Discussion: The current paragraphs (f) and (h) state that the brake

kinetic energy capacity ratings may not be less than the determined

energy absorption requirements. The proposed paragraph (f) would

require the calculation of the necessary energy absorption capacity,

and require dynamometer test substantiation of the capability of the

wheel and brake assemblies to absorb the energy at not less than

specified rates. Usually, brakes are sized to exceed the calculated

energy absorption requirements (i.e., their capacity exceeds the

requirements, hence the heading ``Kinetic energy capacity''). The term

``rating'' would be deleted because it is more relevant to the TSO than

to the regulation. The proposed change would encompass the requirements

of current paragraph (h) without the need for complete duplication of

text.

The term ``rejected takeoff'' used under current paragraph (h)

would be replaced with ``accelerate-stop'' for compatibility with

Sec. 25.109 terminology; and the term ``most severe landing stop''

would be added to address cases such as emergency return to land after

takeoff, where the brake energy for a flaps up landing may exceed that

corresponding to the accelerate-stop energy. For the accelerate-stop

and the most severe landing stop, it is intended that the initial brake

temperature resulting from previous brake use must be accounted for as

specified in paragraphs 3.3.3.3 and 3.3.4.3 in the proposed TSO-C135.

It should be noted that the consideration for the initial temperature

(in terms of residual energy) reflects an existing British Civil

Aviation authority (CAA) Specification 17 requirement. Changing the

term ``main wheel-brake assemblies'' to ``wheel and brake assemblies,''

ensures the paragraph,'' ensures the paragraph's applicability to any

wheels fitted with brakes (i.e., includes the possibility of nose wheel

brakes, etc.) and further ensures the understanding that the absorption

requirements apply to the wheel and brake assembly. The substantiation

statement requires that the wheel and brake assemblies be capable of

absorbing the calculated levels of kinetic energy at the fully worn

limit and that the energy absorption capability substantiation testing

be conducted on the dynamometer.

The current Secs. 25.735(f)(1) and (h)(1) would be incorporated in

proposed AC 25.735-1X, because their content is not strictly part of

the requirement, but provides advice on the primary features that

should be conservatively included in a rational analysis.

The current Secs. 25.735(f)(2) and (h)(2) are not strictly the

requirement, but advice on the method of energy calculation to be used.

Consequently, these would be incorporated in proposed AC 25.735-1X.

Because the required energy capacity of each wheel and brake

assembly must be determined, the need to refer to

[[Page 43574]]

``designed unequal braking distributions'' is no longer necessary and

would be deleted.

The current level of safety would be retained and possibly enhanced

by addressing the most severe landing stop condition. Applicable

advisory material would be included in proposed AC 25.735-1X.

Proposal 12. The FAA proposes to remove the current Sec. 25.735(g)

requirement.

Discussion: The current Sec. 25.735(g) requirement states that when

setting up the dynamometer test inertia, an increase in the initial

brake application speed is not a permissible method of accounting for a

reduced (i.e., lower than ideal) dynamometer mass. This method is not

permissible because, for a target test deceleration, a reduction in the

energy absorption rate would result, and could produce a performance

different from that which would be achieved with the correct brake

application speed. Such a situation is recognized and is similarly

stated in the proposed new TSO-C135, which would provide an acceptable

means for wheel and brake assembly approval under Sec. 25.735(a), thus

making current Sec. 25.735(g) unnecessary. The proposed change

consolidates existing requirements and deletes redundant wording, and

therefore would not impact the current level of safety.

Proposal 13. The FAA proposes to add a new Sec. 24.735(g), ``Brake

condition after high kinetic energy dynamometer stop(s),'' to read:

``(g) Brake condition after high kinetic energy dynamometer

stop(s). Following the high kinetic energy stop demonstration(s)

required by paragraph (f) of this section, with the parking brake

promptly and fully applied for at least three (3) minutes, it must be

demonstrated that for at least five (5) minutes from application of the

parking brake, no condition occurs (or has occurred during the stop),

including fire associated with the tire or wheel and brake assembly,

that could prejudice the safe and complete evacuation of the

airplane.''

Discussion: Paragraph (g) would require that the parking brake be

applied for a minimum of three minutes, which is considered to be the

minimum period of time required to cover the brake's ability to

maintain the airplane in a stationary condition to allow a safe

evacuation.

The requirement also gives consideration to the fact that the

flightcrew may not be aware of the condition of the brake assemblies at

the commencement of the flight, nor of the condition of the brake and

wheel assemblies following the braking maneuver. Furthermore, the

reason for the severe braking could encompass both airplane system and

engine failures or fires. It would therefore appear sensible that it

should be demonstrated that neither during the stop, nor for a

reasonable period of time after its completion, no condition(s) shall

occur as a result of these maneuvers that could further prejudice the

safe and complete evacuation of the airplane. On the basis that an

evacuation may be determined as prudent or necessary, and that such an

evacuation must be capable of completion, irrespective of the timely

response of the emergency services, for minutes would appear to be a

reasonable period of time for the associated brake systems and

equipment to remain free from conditions that might prejudice or

jeopardize the evacuation. It is proposed that this period should

commence at the time of initial application of the parking brake, this

being a time during which the possible need for evacuation and airport

emergency services occurs following an accelerate-stop. The proposed

changes provide for the additional demonstration of a safe condition

following high energy absorption by the wheels and brakes, which was

not previously required. Although previously approved brakes may have

been able to comply with the requirement, approval could not have been

refused had this not been the case. It is therefore believed that the

proposed changes would provide a potential enhancement of the current

level of safety. Applicable advisory material would be included in

proposed AC 25.735-1X.

Proposal 14. The FAA proposes to add a modified version of the

current JAR 25.735(i) as new 14 CFR 25.735(h), ``Stored energy

systems,'' to read:

``(h) Stored energy systems. An indication to the flightcrew of

usable stored energy must be provided if a stored energy system is used

to show compliance with paragraph (b)(1) of this section. The available

stored energy must be sufficient for:

(1) At least six (6) full applications of the brakes when an

antiskid system is not operating; and,

(2) Bringing the airplane to a complete stop when an antiskid

system is operating, under all runway surface conditions for which the

airplane is certificated.''

Discussion: A full brake application is defined as an application

from brakes fully released to brakes fully applied, and back to fully

released. For those airplanes that may provide a number of independent

braking systems, which are not ``reliant'' on a stored energy system

for the demonstration of compliance with paragraph (b)(1) of this

section, but which perhaps incorporate a stored energy device, this

requirement is not applicable. It would be unreasonable that the

requirement for a minimum energy capacity and the provision of means to

indicate the level of stored energy to the flightcrew should be

maintained, particularly if its failure would have a minimal

consequence on airplane or passenger safety.

In the event that an hydraulic accumulator is used for energy

storage and the gas pressurization depletes, a pressure indication

alone as currently required in JAR 25.735(i) would be inadequate

because it would not provide indication of such faults to the

flightcrew. In fact, the current typical flight deck presentation could

give a false sense of security to the crew because it would almost

inevitably indicate a satisfactory pressure, regardless of the real

situation. Consequently, the proposed rule would require a measure of

the stored energy, rather than pressure, to be presented to the

flightcrew.

The minimum level of stored energy required for the emergency/

standby braking means would be presented as a requirement rather than

as advisory material. In the majority of cases, this material has been

used as a virtual requirement in the past by airplane manufacturers and

regulatory authorities. The proposed change would potentially enhance

the current level of safety because the FAA is proposing to adopt a

common but not universal industry practice and an improvement over the

existing JAR rule. Applicable advisory material would be included in

the proposed new AC 25.735-1X.

Proposal 15. The FAA proposes to add a new Sec. 25.735(i), ``Brake

wear indicators,'' to read:

``(i) Brake wear indicators. Means must be provided for each brake

assembly to indicate when the heat sink is worn to the permissible

limit. The means must be reliable and readily visible.''

Discussion: In order to ensure, as far as is practicable, that the

brake heat sink is not worn beyond its allowable wear limits throughout

its operational life, it is considered necessary to provide some device

that can readily identify the fully worn limit of the heat sink. The

proposal reflects a requirement included in a series of airworthiness

directives issued between 1989 and 1994 to require establishment of

brake wear limits and to provide means to indicate the same. The

British Civil Aviation Authority (CAA) Specification No. 17

[[Page 43575]]

also specifies the provision of such an indicator, and the majority of

wheel and brake assembly designs include such a device. The proposed

rule would have no impact on the current level of safety, because the

FAA is proposing to adopt an existing industry practice. Appropriate

advisory information would be included in proposed AC 25.735-1X.

Proposal 16. The FAA proposes to add a new Sec. 25.735(j),

``Overtemperature burst prevention,'' a new Sec. 25.731(d),

``Overpressure burst prevention,'' and a new Sec. 25.731(e), ``Braked

wheels,'' to read as follows:

``Sec. 25.735(j) Overtemperature burst prevention. Means must be

provided in each braked wheel to prevent wheel failure and tire burst

that may result from elevated brake temperatures. Additionally, all

wheels must meet the requirements of Sec. 25.731(d).''

``Sec. 25.731(d) Overpressure burst prevention. Means must be

provided in each wheel to prevent wheel failure and tire burst that may

result from excessive pressurization of the wheel and tire assembly.''

``Sec. 25.731(e) Braked wheels. Each braked wheel must meet the

applicable requirements of Sec. 25.735.''

Discussion--Sec. 25.735(j): There is an existing requirement

(Sec. 25.729(f)) related to the protection of equipment in wheel wells

against the effects of bursting tires and a similar requirement is

stated in TSO-C26c, Wheels and Wheel-Brake Assemblies. JAR 25.729(f)

requires protection of equipment on the landing gear and in wheel wells

against tire burst and elevated brake temperatures, and a similar

requirement is stated in the ``Minimum Operational Performance

Specification for Wheels and Brakes on JAR Part 25 Civil Aeroplanes''

(Document ED-69). However, there is no direct requirement in either

part 25 or JAR-25 that means must be provided to prevent wheel failure

and tire burst that could result from elevated brake temperatures. As a

result, it has become an industry practice to incorporate pressure

release device(s) that function as a result of elevated wheel

temperatures to deflate the tires. Nevertheless, it is believed to be

both reasonable and prudent that such a requirement should be clearly

stated in the paragraph related to airplane brakes and braking systems.

The proposed requirement for temperature activated devices would not

impact the current level of safety. Applicable advisory information

would be included in proposed AC 25.735-1X.

Discussion--Sec. 25.731(d): Wheel failure and tire burst due to

over-inflation presents a hazard to ground personnel and the airplane.

Certain airplane manufacturers require wheel pressure release devices

that reduce this hazard. This is considered a safety issue requiring

the incorporation of these devices. Incorporation of pressure release

devices in tire inflation equipment is not considered adequate due to a

history of misuse resulting in serious injuries or fatalities.

Installation in the wheel reduces the potential for tampering or misuse

and insures proper levels of protection. The proposed change would

retain and potentially enhance the current level of safety. Applicable

advisory information would be included in proposed AC 25.735-1X.

Discussion--25.731(e): This section contains regulations applicable

to all airplane wheels. If the wheel is braked, additional regulations

apply, which are contained in Sec. 25.735. Section 25.731(e) is added

to provide a cross-reference to those additional requirements. The

proposed change would retain and potentially enhance the current level

of safety.

Proposal 17. The FAA proposes to add a new Sec. 25.735(k),

``Compatibility,'' to read:

``(k) Compatibility. Compatibility of the wheel and brake

assemblies with the airplane and its systems must be substantiated.''

Discussion: Reliable and consistent brake system performance can be

adversely affected by incompatibilities within the system and with the

landing gear and the airplane. As part of the overall substantiation of

safe and anomaly free operation, it is necessary to show that no unsafe

conditions arise from incompatibilities between the brakes and brake

system with other airplane systems and structures. Areas such as

antiskid tuning, landing gear dynamics, tire type and size, brake

combinations, brake characteristics, brake and landing gear vibrations,

etc., need to be explored and corrected if necessary. Therefore, this

requirement is introduced to address these issues which are normally

covered by airplane manufacturers during development of the airplane

and must be addressed by modifiers of the equipment. Incorporation of

this requirement would potentially enhance the current level of safety.

Appropriate advisory information would be included in proposed AC

25.735-1X.

Paperwork Reduction Act

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

3507(d)), the FAA has determined that there are no requirements for

information collection associated with this proposed rule.

Compatibility With ICAO Standards

In keeping with U.S. obligations under the Convention on

International Civil Aviation, it is FAA policy to comply with

International Civil Aviation Organization (ICAO) Standards and

Recommended practices to the maximum extent practicable. The FAA has

determined that there are no ICAO Standards and Recommended Practices

that correspond to these proposed 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 (OMB) directs agencies to assess the

effect of regulatory changes on international trade. In conducting

these analyses, the FAA has determined that this proposed rule is not

``a significant regulatory action'' under section 3(f) of Executive

Order 12866 and, therefore, is not subject to review by OMB. 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.

Although numerous revisions would be made to Sec. 25.735, only one

would impose additional quantified costs for both part 25 large and

small airplane manufacturers (see below--proposal 11). One ARAC member,

a manufacturer of part 25 small airplanes, claimed that proposals 7,

14, and 16 would also impose incremental costs, but provided no

specific estimates (these proposals are also discussed below).

Essentially all of the changes codify current industry practice or

conform 14 CFR 25.735 to corresponding sections of the JAR. Adoption of

the proposed changes would increase harmonization and commonality

between American and European airworthiness standards, thus enhancing

safety. Harmonization would eliminate unnecessary duplication of

[[Page 43576]]

airworthiness requirements, thus reducing manufacturers' certification

costs (6 substantive proposals out of 17 total in the subject NPRM

would essentially mirror the proposed European standards; the 11 others

would not differ significantly). The FAA believes the enhanced safety

benefits and harmonization cost savings would exceed the relatively low

incremental costs of the proposed rule (see Summary of Costs and

Benefits section below).

Proposal 7. Changes regarding parking brake control and cockpit

indication of the brake essentially reflect current industry practice

for the majority of part 25 manufacturers; consequently, there are no

expected incremental costs. As noted above, one manufacture of part 25

small airplanes, however, indicated that its current designs do not

meet this requirement and that costs for cockpit indication in future

designs would, in fact, be incremental. The manufacturer, however, did

not provide such costs to the FAA. The FAA invites that manufacture

(and/or other interested parties) to provide detailed cost estimates

during the public comment period.

Proposal 11. One ARAC member, a manufacturer of part 25 large

airplanes, notes that the average impact of the 10 percent residual

rejected takeoff energy requirement would be a 2 to 3 percent increase

in the brake's energy absorption requirements. Notwithstanding, this

increase is smaller than the tolerances on its ability to define brake

requirements and the brake manufacturer's conformance to the

specifications. Also, higher residual energies would enable the

manufacturer to raise its recommended brake temperatures for dispatch,

so any potential higher brake costs would be offset by more efficient

aircraft operation (shorter turnaround times, less time at gate waiting

for brakes to cool).

The term ``most severe landing stop'' (MSL) would be added to

address cases such as immediate return to land after takeoff where the

brake energy for a flaps up landing may exceed that corresponding to

the accelerate-stop energy. The MSL requirement, while a new FAA

requirement, has been in effect in Europe (per British CAA);

consequently, many large part 25 airplane manufacturers currently meet

this standard. Notwithstanding, large part 25 airframe and brake

manufacturers note that in almost all cases either the MSL stop energy

would not exceed the maximum kinetic energy accelerate-stop energy, or

the MSL stop condition is extremely improbable. One part 25 large

airplane manufacturer, however, noted that demonstrating adherence to

this requirement for its typical airplane model would add the

equivalent of two additional high-energy dynamometers tests in which

the test brake would be destroyed; estimated incremental one-time costs

for this equal approximately $60,000 per type certification. Another

manufacturer, however, estimates only one test in the $20,000-$40,000

range. Manufacturers of small part 25 airplanes would experience some

incremental one-time testing costs totaling approximately $20,000 per

type certification.

The aforementioned nonrecurring costs for either the part 25 large

or small airplane type certification would easily be offset by the

harmonization cost savings cited earlier. Any potential safety benefits

from avoiding even one minor accident would add to such benefits. The

FAA therefore finds proposal 11 to be cost beneficial.

Proposal 14. As the stored energy requirement reflects current

industry practice for most part 25 manufacturers, there would be no

expected incremental costs associated with it. However, the same

manufacturer (of part 25 small airplanes) that reported potential costs

for proposal 7, also indicated that its current designs do not include

usable stored energy indication, and compliance with this requirement

in future designs would impose incremental costs. Detailed cost

estimates, however, were not provided. The FAA requests that the

manufacturers (or others) provide detailed costs estimates during the

public comment period.

Proposal 16. In the last several years, many wheel manufacturers

have included pressure release devices in most new production wheels in

order to avoid potential liability. Codification of existing industry

practice would ensure that the enhanced level of safety is retained.

There are no expected incremental costs associated with this proposal

since it does reflect current industry practice. However, the same

manufacturer (of part 25 small airplanes) that, in contrast to other

manufacturers, reported potential costs for proposals 7 and 14

indicated that the requirement for wheel pressure release devices would

also impose incremental costs in future designs. Again, the FAA invites

that manufacturer (or others) to provide detailed cost estimates during

the public comment period.

Summary of Costs and Benefits

As delineated above, and barring more detailed information for

proposals 7, 14, and 16, the FAA concludes that only proposal 11 would

result in incremental costs attributable to the subject NPRM.

Demonstrating adherence to the MSL requirement would increase

nonrecurring testing costs from $20,000-$60,000 for a part 25 large

airplane type certification; the amount for a part 25 small airplane

type certification is estimated to be $20,000. According to one

manufacturer, cost savings from harmonization, in terms of avoiding

added costs of coordination and documentation (with the JAA and

involving, for example, additional travel overseas, reports, etc.)

would be equal to or greater than the maximum incremental cost of

$60,000. The FAA believes that potential safety benefits resulting form

specification of minimum accepted standards would supplement these

cost-savings. Although there were numerous (approx. 170) accidents

involving brake failures during landings in the period 1982-1995, none

were determined to have been directly preventable by the subject

provisions. Different designs in future type certifications, however,

could present other problems (unexpected) and raise future accident

rates. This proposed rule is expected to reduce the chances of future

accidents by codifying in 14 CFR part 25 (and therefore making

mandatory) what was prevailing, but not necessarily universal, industry

practice.

For the reasons specified, the FAA finds the proposed rule to be

cost-beneficial.

Initial Regulatory Flexibility Determination

The Regulatory Flexibility Act of 1980 (RFA) 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, organizations, and governmental jurisdictions subject to

regulation.'' To achieve that principle, 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 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

[[Page 43577]]

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 a

regulatory flexibility analysis 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 part 25 transport

category airplanes produced under future new airplane type

certifications. For manufacturers, a small entity is one with 1,500 or

fewer employees. No part 25 airplane manufacturer has 1,500 or fewer

employees. Notwithstanding, the relatively low annualized incremental

certification costs are not considered significant within the meaning

of the RFA. Consequently, the FAA certifies that the proposed rule

would not have a significant economic impact on a substantial number of

manufacturers identified as small entities.

International Trade Impact Statement

The provisions of this proposed rule would have little or no impact

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

firms doing business in the United States.

This proposed rule is a direct action to respond to this policy by

increasing the harmonization of the U.S. Federal Aviation Regulations

with the European Joint Aviation Requirements. The result would be a

positive step toward removing impediments to international trade.

Federalism Implications

The regulations proposed herein would not have a substantial direct

effect 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. Therefore, in

accordance with executive Order 12612, it is determined that this

proposal would 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 1 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) or 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 1 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

develop 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 in any 1 year.

Environmental Analysis

FAA 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 action 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.

Regulations Affecting Intrastate Aviation in Alaska

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

3213) requires the Administrator, when modifying regulations in Title

14 of the CFR in manner affecting intrastate 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 intrastate aviation in Alaska. The FAA therefore

specifically requests comments on whether there is justification for

applying the proposed rule differently to intrastate operations in

Alaska.

List of Subjects in 14 CFR Part 25

Aircraft, Aviation safety, Reporting and recordkeeping

requirements.

The Proposed Amendment

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, 44704.

2. Amend Sec. 25.731 to add new paragraphs (d) and (e) to read as

follows:

Sec. 25.731 Wheels.

* * * * *

(d) Overpressure burst prevention. Means must be provided in each

wheel to prevent wheel failure and tire burst that may result from

excessive pressurization of the wheel and tire assembly.

(e) Braked Wheels. Each braked wheel must meet the applicable

requirements of Sec. 24.735.

3. Revise Sec. 25.735 to read as follows:

Sec. 25.735 Brakes and braking systems.

(a) Approval. Each assembly consisting of a wheel(s) and brake(s)

must be approved.

(b) Brake system capability. The brake system, associated systems

and components must be designed and constructed so that:

(1) If any electrical, pneumatic, hydraulic, or mechanical

connecting or transmitting element fails, or if any single source of

hydraulic or other brake operating energy supply is lost, it is

possible to bring the airplane to rest with a braked roll stopping

distance of not more than two times that obtained in determining the

landing distance as prescribed in Sec. 25.125.

(2) Fluid lost from a brake hydraulic system following a failure

in, or in the vicinity of, the brakes is insufficient to cause or

support a hazardous fire on the ground or in flight.

(c) Brake controls. The brake controls must be designed and

constructed so that:

(1) Excessive control force is not required for their operation.

[[Page 43578]]

(2) If an automatic braking system is installed, means are provided

to:

(i) Arm and disarm the system, and

(ii) Allow the pilot(s) to override the system by use of manual

braking.

(d) Parking brake. The airplane must have a parking brake control

that, when selected on, will, without further attention, prevent the

airplane from rolling on a dry and level paved runway when the most

adverse combination of maximum thrust on one engine and up to maximum

ground idle thrust on any, or all, other engine(s) is applied. The

control must be suitably located or be adequately protected to prevent

inadvertent operation. There must be indication in the cockpit when the

parking brake is not fully released.

(e) Antiskid system. If an antiskid system is installed:

(1) It must operate satisfactory over the range of expected runway

conditions, without external adjustment.

(2) It must, at all times, have priority over the automatic braking

system, if installed.

(f) Kinetic energy capacity. The design landing stop, the maximum

kinetic energy accelerate-stop, and the most severe landing stop brake

kinetic energy absorption requirements of each wheel and brake assembly

must be determined. It must be substantiated by dynamometer testing

that, at the declared fully worn limit(s) of the brake heat sink, the

wheel and brake assemblies are capable of absorbing not less than these

levels of kinetic energy. Energy absorption rates defined by the

airplane manufacturer must be achieved. These rates must be equivalent

to mean decelerations not less than 10 fps\2\ for the design landing

stop and 6 fps\2\ for the maximum kinetic energy accelerate stop. The

most severe landing stop need not be considered for extremely

improbable failure conditions or if the maximum kinetic energy

accelerate-stop energy is more severe. Design landing stop is an

operational landing stop at maximum landing weight. Maximum kinetic

energy accelerate-stop is a rejected takeoff for the most critical

combination of airplane takeoff weight and speed. Most severe landing

stop is a stop at the most critical combination of airplane landing

weight and speed.

(g) Brake condition after high kinetic energy dynamometer stop(s).

Following the high kinetic energy stop demonstration(s) required by

paragraph (f) of this section, with the parking brake promptly and

fully applied for at least three (3) minutes, it must be demonstrated

that for at least five (5) minutes from application of the parking

brake, no condition occurs (or has occurred during the stop), including

fire associated with the tire or wheel and brake assembly, that could

prejudice the safe and complete evacuation of the airplane.

(h) Stored energy systems. An indication to the flightcrew of the

usable stored energy must be provided if a stored energy system is used

to show compliance with paragraph (b)(1) of this section. The available

stored energy must be sufficient for:

(1) At least six (6) full applications of the brakes when a

antiskid system is not operating; and

(2) Bringing the airplane to a complete stop when an antiskid

system is operating, under all runway surface conditions for which the

airplane is certificated.

(i) Brake wear indicators. Means must be provided for each brake

assembly to indicate when the heat sink is worn to the permissible

limit. The means must be reliable and readily visible.

(j) Overtemperature burst prevention. Means must be provided in

each braked wheel to prevent wheel failure and tire burst that may

result from elevated brake temperatures. Additionally, all wheels must

meet the requirements of Sec. 25.731(d).

(k) Compatibility. Compatibility of the wheel and brake assemblies

with the airplane and its systems must be substantiated.

Issued in Washington, DC, on August 3, 1999.

Ronald T. Wojnar,

Deputy Director, Aircraft Certification Service.

[FR Doc. 99-20518 Filed 8-9-99; 8:45 am]

BILLING CODE 4910-13-M