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

[Federal Register Volume 64, Number 153 (Tuesday, August 10, 1999)]
[Proposed Rules]
[Pages 43570-43578]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-20518]



[[Page 43569]]

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Part VIII





Department of Transportation





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Federal Aviation Administration



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14 CFR Part 25



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



Proposed Technical Standard Order (TSO)-C135, Transport Airplane Wheels 
and Wheel and Brake Assemblies; Proposed Rule



Proposed Advisory Circular (AC) 25.735-1X, Brakes and Braking Systems 
Certification Tests and Analysis; Proposed Rule

Federal Register / Vol. 64, No. 153 / Tuesday, August 10, 1999 / 
Proposed Rules

[[Page 43570]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-1999-6063; Notice No. 99-16]
RIN 2120-AG80


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking.

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

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