title-14-part-25-sec25-519

254

14 CFR Ch. I (1–1–24 Edition)

§ 25.519

distribution on the wheels, may be ne-
glected.

(b)

Distribution of limit loads to wheels;

tires inflated. The distribution of the
limit loads among the wheels of the
landing gear must be established for
each landing, taxiing, and ground han-
dling condition, taking into account
the effects of the following factors:

(1) The number of wheels and their

physical arrangements. For truck type
landing gear units, the effects of any
seesaw motion of the truck during the
landing impact must be considered in
determining the maximum design loads
for the fore and aft wheel pairs.

(2) Any differentials in tire diameters

resulting from a combination of manu-
facturing tolerances, tire growth, and
tire wear. A maximum tire-diameter
differential equal to

⁄

of the most un-

favorable combination of diameter
variations that is obtained when tak-
ing into account manufacturing toler-
ances, tire growth, and tire wear, may
be assumed.

(3) Any unequal tire inflation pres-

sure, assuming the maximum variation
to be

5 percent of the nominal tire in-

flation pressure.

(4) A runway crown of zero and a run-

way crown having a convex upward
shape that may be approximated by a
slope of 1

⁄

percent with the hori-

zontal. Runway crown effects must be
considered with the nose gear unit on
either slope of the crown.

(5) The airplane attitude.
(6) Any structural deflections.
(c)

Deflated tires. The effect of de-

flated tires on the structure must be
considered with respect to the loading
conditions specified in paragraphs (d)
through (f) of this section, taking into
account the physical arrangement of
the gear components. In addition—

(1) The deflation of any one tire for

each multiple wheel landing gear unit,
and the deflation of any two critical
tires for each landing gear unit using
four or more wheels per unit, must be
considered; and

(2) The ground reactions must be ap-

plied to the wheels with inflated tires
except that, for multiple-wheel gear
units with more than one shock strut,
a rational distribution of the ground
reactions between the deflated and in-
flated tires, accounting for the dif-

ferences in shock strut extensions re-
sulting from a deflated tire, may be
used.

(d)

Landing conditions. For one and

for two deflated tires, the applied load
to each gear unit is assumed to be 60
percent and 50 percent, respectively, of
the limit load applied to each gear for
each of the prescribed landing condi-
tions. However, for the drift landing
condition of § 25.485, 100 percent of the
vertical load must be applied.

(e)

Taxiing and ground handling condi-

tions. For one and for two deflated
tires—

(1) The applied side or drag load fac-

tor, or both factors, at the center of
gravity must be the most critical value
up to 50 percent and 40 percent, respec-
tively, of the limit side or drag load
factors, or both factors, corresponding
to the most severe condition resulting
from consideration of the prescribed
taxiing and ground handling condi-
tions;

(2) For the braked roll conditions of

§ 25.493 (a) and (b)(2), the drag loads on
each inflated tire may not be less than
those at each tire for the symmetrical
load distribution with no deflated tires;

(3) The vertical load factor at the

center of gravity must be 60 percent
and 50 percent, respectively, of the fac-
tor with no deflated tires, except that
it may not be less than 1g; and

(4) Pivoting need not be considered.
(f)

Towing conditions. For one and for

two deflated tires, the towing load,
F

TOW,

must be 60 percent and 50 percent,

respectively, of the load prescribed.

§ 25.519

Jacking and tie-down provi-

sions.

(a) General. The airplane must be de-

signed to withstand the limit load con-
ditions resulting from the static
ground load conditions of paragraph (b)
of this section and, if applicable, para-
graph (c) of this section at the most
critical combinations of airplane
weight and center of gravity. The max-
imum allowable load at each jack pad
must be specified.

(b) Jacking. The airplane must have

provisions for jacking and must with-
stand the following limit loads when
the airplane is supported on jacks—

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255

Federal Aviation Administration, DOT

§ 25.527

(1) For jacking by the landing gear at

the maximum ramp weight of the air-
plane, the airplane structure must be
designed for a vertical load of 1.33
times the vertical static reaction at
each jacking point acting singly and in
combination with a horizontal load of
0.33 times the vertical static reaction
applied in any direction.

(2) For jacking by other airplane

structure at maximum approved jack-
ing weight:

(i) The airplane structure must be de-

signed for a vertical load of 1.33 times
the vertical reaction at each jacking
point acting singly and in combination
with a horizontal load of 0.33 times the
vertical static reaction applied in any
direction.

(ii) The jacking pads and local struc-

ture must be designed for a vertical
load of 2.0 times the vertical static re-
action at each jacking point, acting
singly and in combination with a hori-
zontal load of 0.33 times the vertical
static reaction applied in any direc-
tion.

provided, the main tie-down points and
local structure must withstand the
limit loads resulting from a 65-knot
horizontal wind from any direction.

[Doc. No. 26129, 59 FR 22102, Apr. 28, 1994]

ATER

OADS

§ 25.521

General.

(a) Seaplanes must be designed for

the water loads developed during take-
off and landing, with the seaplane in
any attitude likely to occur in normal
operation, and at the appropriate for-
ward and sinking velocities under the
most severe sea conditions likely to be
encountered.

(b) Unless a more rational analysis of

the water loads is made, or the stand-
ards in ANC–3 are used, §§ 25.523
through 25.537 apply.

and §§ 25.523 through 25.537 apply also to
amphibians.

§ 25.523

Design weights and center of

gravity positions.

(a)

Design weights. The water load re-

quirements must be met at each oper-
ating weight up to the design landing
weight except that, for the takeoff con-

dition prescribed in § 25.531, the design
water takeoff weight (the maximum
weight for water taxi and takeoff run)
must be used.

(b)

Center of gravity positions. The

critical centers of gravity within the
limits for which certification is re-
quested must be considered to reach
maximum design loads for each part of
the seaplane structure.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5673, Apr. 8,
1970]

§ 25.525

Application of loads.

(a) Unless otherwise prescribed, the

seaplane as a whole is assumed to be
subjected to the loads corresponding to
the load factors specified in § 25.527.

(b) In applying the loads resulting

from the load factors prescribed in
§ 25.527, the loads may be distributed
over the hull or main float bottom (in
order to avoid excessive local shear
loads and bending moments at the lo-
cation of water load application) using
pressures not less than those pre-
scribed in § 25.533(c).

float must be treated as an equivalent
hull on a fictitious seaplane with a
weight equal to one-half the weight of
the twin float seaplane.

(d) Except in the takeoff condition of

§ 25.531, the aerodynamic lift on the
seaplane during the impact is assumed
to be

⁄

of the weight of the seaplane.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Doc. No. FAA–2022–1355, Amdt.
25–148, 87 FR 75710, Dec. 9, 2022; 88 FR 2813,
Jan. 18, 2023]

§ 25.527

Hull and main float load fac-

tors.

(a) Water reaction load factors

must be computed in the following
manner:

(1) For the step landing case

C V

⎛

⎝

⎞

⎠

2
3

1
3

Tan

(2) For the bow and stern landing

cases