title-14-part-25-sec25-733

274

14 CFR Ch. I (1–1–24 Edition)

§ 25.731

(2) A loose tire tread, unless it is

shown that a loose tire tread cannot
cause damage.

(3) Possible wheel brake tempera-

tures.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5676, Apr. 8,
1970; Amdt. 25–42, 43 FR 2323, Jan. 16, 1978;
Amdt. 25–72, 55 FR 29777, July 20, 1990; Amdt.
25–75, 56 FR 63762, Dec. 5, 1991; Amdt. 25–136,
77 FR 1617, Jan. 11, 2012]

§ 25.731

Wheels.

(a) Each main and nose wheel must

be approved.

(b) The maximum static load rating

of each wheel may not be less than the
corresponding static ground reaction
with—

(1) Design maximum weight; and
(2) Critical center of gravity.
(c) The maximum limit load rating of

each wheel must equal or exceed the
maximum radial limit load determined
under the applicable ground load re-
quirements of this part.

(d)

Overpressure burst prevention.

Means must be provided in each wheel
to prevent wheel failure and tire burst
that may result from excessive pressur-
ization of the wheel and tire assembly.

(e)

Braked wheels. Each braked wheel

must meet the applicable requirements
of § 25.735.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–72, 55 FR 29777, July 20,
1990; Amdt. 25–107, 67 FR 20420, Apr. 24, 2002]

§ 25.733

Tires.

(a) When a landing gear axle is fitted

with a single wheel and tire assembly,
the wheel must be fitted with a suit-
able tire of proper fit with a speed rat-
ing approved by the Administrator
that is not exceeded under critical con-
ditions and with a load rating approved
by the Administrator that is not ex-
ceeded under—

(1) The loads on the main wheel tire,

corresponding to the most critical
combination of airplane weight (up to
maximum weight) and center of grav-
ity position, and

(2) The loads corresponding to the

ground reactions in paragraph (b) of
this section, on the nose wheel tire, ex-
cept as provided in paragraphs (b)(2)
and (b)(3) of this section.

(b) The applicable ground reactions

for nose wheel tires are as follows:

(1) The static ground reaction for the

tire corresponding to the most critical
combination of airplane weight (up to
maximum ramp weight) and center of
gravity position with a force of 1.0g
acting downward at the center of grav-
ity. This load may not exceed the load
rating of the tire.

(2) The ground reaction of the tire

corresponding to the most critical
combination of airplane weight (up to
maximum landing weight) and center
of gravity position combined with
forces of 1.0g downward and 0.31g for-
ward acting at the center of gravity.
The reactions in this case must be dis-
tributed to the nose and main wheels
by the principles of statics with a drag
reaction equal to 0.31 times the
vertical load at each wheel with brakes
capable of producing this ground reac-
tion. This nose tire load may not ex-
ceed 1.5 times the load rating of the
tire.

(3) The ground reaction of the tire

corresponding to the most critical
combination of airplane weight (up to
maximum ramp weight) and center of
gravity position combined with forces
of 1.0g downward and 0.20g forward act-
ing at the center of gravity. The reac-
tions in this case must be distributed
to the nose and main wheels by the
principles of statics with a drag reac-
tion equal to 0.20 times the vertical
load at each wheel with brakes capable
of producing this ground reaction. This
nose tire load may not exceed 1.5 times
the load rating of the tire.

with more than one wheel and tire as-
sembly, such as dual or dual-tandem,
each wheel must be fitted with a suit-
able tire of proper fit with a speed rat-
ing approved by the Administrator
that is not exceeded under critical con-
ditions, and with a load rating ap-
proved by the Administrator that is
not exceeded by—

(1) The loads on each main wheel

tire, corresponding to the most critical
combination of airplane weight (up to
maximum weight) and center of grav-
ity position, when multiplied by a fac-
tor of 1.07; and

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Federal Aviation Administration, DOT

§ 25.735

(2) Loads specified in paragraphs

(a)(2), (b)(1), (b)(2), and (b)(3) of this
section on each nose wheel tire.

(d) Each tire installed on a retract-

able landing gear system must, at the
maximum size of the tire type expected
in service, have a clearance to sur-
rounding structure and systems that is
adequate to prevent unintended con-
tact between the tire and any part of
the structure or systems.

(e) For an airplane with a maximum

certificated takeoff weight of more
than 75,000 pounds, tires mounted on
braked wheels must be inflated with
dry nitrogen or other gases shown to be
inert so that the gas mixture in the
tire does not contain oxygen in excess
of 5 percent by volume, unless it can be
shown that the tire liner material will
not produce a volatile gas when heated
or that means are provided to prevent
tire temperatures from reaching unsafe
levels.

[Amdt. 25–48, 44 FR 68752, Nov. 29, 1979; Amdt.
25–72, 55 FR 29777, July 20, 1990, as amended
by Amdt. 25–78, 58 FR 11781, Feb. 26, 1993]

§ 25.735

Brakes and braking systems.

(a)

Approval. Each assembly con-

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

(b)

Brake system capability. The brake

system, associated systems and compo-
nents must be designed and con-
structed so that:

(1) If any electrical, pneumatic, hy-

draulic, 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 dis-
tance of not more than two times that
obtained in determining the landing
distance as prescribed in § 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 re-

quired for their operation.

(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 inad-
vertent operation. There must be indi-
cation in the cockpit when the parking
brake is not fully released.

(e)

Antiskid system. If an antiskid sys-

tem is installed:

(1) It must operate satisfactorily over

the range of expected runway condi-
tions, without external adjustment.

(2) It must, at all times, have pri-

ority over the automatic braking sys-
tem, if installed.

(f)

Kinetic energy capacity—(1) Design

landing stop. The design landing stop is
an operational landing stop at max-
imum landing weight. The design land-
ing stop brake kinetic energy absorp-
tion requirement of each wheel, brake,
and tire assembly must be determined.
It must be substantiated by dynamom-
eter testing that the wheel, brake and
tire assembly is capable of absorbing
not less than this level of kinetic en-
ergy throughout the defined wear
range of the brake. The energy absorp-
tion rate derived from the airplane
manufacturer’s braking requirements
must be achieved. The mean decelera-
tion must not be less than 10 fps

(2)

Maximum kinetic energy accelerate-

stop. The maximum kinetic energy ac-
celerate-stop is a rejected takeoff for
the most critical combination of air-
plane takeoff weight and speed. The ac-
celerate-stop brake kinetic energy ab-
sorption requirement of each wheel,
brake, and tire assembly must be de-
termined. It must be substantiated by
dynamometer testing that the wheel,
brake, and tire assembly is capable of
absorbing not less than this level of ki-
netic energy throughout the defined
wear range of the brake. The energy
absorption rate derived from the air-
plane manufacturer’s braking require-
ments must be achieved. The mean de-
celeration must not be less than 6 fps