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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. 

(c) Tie-down. If tie-down points are 

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] 

W

ATER

L

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. 

(c) The requirements of this section 

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). 

(c) For twin float seaplanes, each 

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 

2

3

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 

n

W

 

must be computed in the following 
manner: 

(1) For the step landing case 

n

C V

W

w

S

=

1

0

2

2
3

1
3

Tan

β

(2) For the bow and stern landing 

cases 

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256 

14 CFR Ch. I (1–1–24 Edition) 

§ 25.529 

n

C V

W

K

r

w

S

x

=

×

+

(

)

1

0

1

2

2

2
3

1
3

2
3

1

Tan

β

(b) The following values are used: 
(1) 

n

W

= water reaction load factor 

(that is, the water reaction divided by 
seaplane weight). 

(2) 

C

1

= empirical seaplane operations 

factor equal to 0.012 (except that this 
factor may not be less than that nec-
essary to obtain the minimum value of 
step load factor of 2.33). 

(3) 

V

S0

= seaplane stalling speed in 

knots with flaps extended in the appro-
priate landing position and with no 
slipstream effect. 

(4) 

= angle of dead rise at the longi-

tudinal station at which the load fac-
tor is being determined in accordance 
with figure 1 of appendix B. 

(5) 

W= 

seaplane design landing 

weight in pounds. 

(6) 

K

1

= empirical hull station weigh-

ing factor, in accordance with figure 2 
of appendix B. 

(7) 

r

x

= ratio of distance, measured 

parallel to hull reference axis, from the 
center of gravity of the seaplane to the 
hull longitudinal station at which the 
load factor is being computed to the ra-
dius of gyration in pitch of the sea-
plane, the hull reference axis being a 
straight line, in the plane of sym-
metry, tangential to the keel at the 
main step. 

(c) For a twin float seaplane, because 

of the effect of flexibility of the attach-
ment of the floats to the seaplane, the 
factor 

K

1

may be reduced at the bow 

and stern to 0.8 of the value shown in 
figure 2 of appendix B. This reduction 
applies only to the design of the carry-
through and seaplane structure. 

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

§ 25.529

Hull and main float landing 

conditions. 

(a) 

Symmetrical step, bow, and stern 

landing.  For symmetrical step, bow, 
and stern landings, the limit water re-
action load factors are those computed 
under § 25.527. In addition— 

(1) For symmetrical step landings, 

the resultant water load must be ap-

plied at the keel, through the center of 
gravity, and must be directed per-
pendicularly to the keel line; 

(2) For symmetrical bow landings, 

the resultant water load must be ap-
plied at the keel, one-fifth of the longi-
tudinal distance from the bow to the 
step, and must be directed perpendicu-
larly to the keel line; and 

(3) For symmetrical stern landings, 

the resultant water load must be ap-
plied at the keel, at a point 85 percent 
of the longitudinal distance from the 
step to the stern post, and must be di-
rected perpendicularly to the keel line. 

(b) 

Unsymmetrical landing for hull and 

single float seaplanes. Unsymmetrical 
step, bow, and stern landing conditions 
must be investigated. In addition— 

(1) The loading for each condition 

consists of an upward component and a 
side component equal, respectively, to 
0.75 and 0.25 tan 

times the resultant 

load in the corresponding symmetrical 
landing condition; and 

(2) The point of application and di-

rection of the upward component of the 
load is the same as that in the sym-
metrical condition, and the point of ap-
plication of the side component is at 
the same longitudinal station as the 
upward component but is directed in-
ward perpendicularly to the plane of 
symmetry at a point midway between 
the keel and chine lines. 

(c) 

Unsymmetrical landing; twin float 

seaplanes.  The unsymmetrical loading 
consists of an upward load at the step 
of each float of 0.75 and a side load of 
0.25 tan 

at one float times the step 

landing load reached under § 25.527. The 
side load is directed inboard, per-
pendicularly to the plane of symmetry 
midway between the keel and chine 
lines of the float, at the same longitu-
dinal station as the upward load. 

§ 25.531

Hull and main float takeoff 

condition. 

For the wing and its attachment to 

the hull or main float— 

(a) The aerodynamic wing lift is as-

sumed to be zero; and 

(b) A downward inertia load, cor-

responding to a load factor computed 
from the following formula, must be 
applied: 

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