259
Federal Aviation Administration, DOT
§ 25.561
(e)
Unsymmetrical bow loading.
The re-
sultant water load consists of a compo-
nent equal to 0.75 times the load speci-
fied in paragraph (b) of this section and
a side component equal to 0.25 tan
b
times the load specified in paragraph
(c) of this section. The side load must
be applied perpendicularly to the plane
of symmetry at a point midway be-
tween the keel and the chine.
(f)
Immersed float condition.
The re-
sultant load must be applied at the
centroid of the cross section of the
float at a point one-third of the dis-
tance from the bow to the step. The
limit load components are as follows:
vertical
aft
side
=
=
=
ρ
ρ
ρ
g
x
y
V
C
V
KV
C
V
KV
S
S
2
2
2
2
2
3
0
2
3
0
where—
r
= mass density of water (slugs/ft.
2
);
V
= volume of float (ft.
2
);
C
x
= coefficient of drag force, equal to 0.133;
C
y
= coefficient of side force, equal to 0.106;
K
= 0.8, except that lower values may be used
if it is shown that the floats are incapa-
ble of submerging at a speed of 0.8
V
S
0
in
normal operations;
V
S
0
= seaplane stalling speed (knots) with
landing flaps extended in the appropriate
position and with no slipstream effect;
and
g
= acceleration due to gravity (ft./sec.
2
).
(g)
Float bottom pressures.
The float
bottom pressures must be established
under § 25.533, except that the value of
K
2
in the formulae may be taken as 1.0.
The angle of dead rise to be used in de-
termining the float bottom pressures is
set forth in paragraph (b) of this sec-
tion.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5673, Apr. 8,
1970]
§ 25.537
Seawing loads.
Seawing design loads must be based
on applicable test data.
E
MERGENCY
L
ANDING
C
ONDITIONS
§ 25.561
General.
(a) The airplane, although it may be
damaged in emergency landing condi-
tions on land or water, must be de-
signed as prescribed in this section to
protect each occupant under those con-
ditions.
(b) The structure must be designed to
give each occupant every reasonable
chance of escaping serious injury in a
minor crash landing when—
(1) Proper use is made of seats, belts,
and all other safety design provisions;
(2) The wheels are retracted (where
applicable); and
(3) The occupant experiences the fol-
lowing ultimate inertia forces acting
separately relative to the surrounding
structure:
(i) Upward, 3.0g
(ii) Forward, 9.0g
(iii) Sideward, 3.0g on the airframe;
and 4.0g on the seats and their attach-
ments.
(iv) Downward, 6.0g
(v) Rearward, 1.5g
(c) For equipment, cargo in the pas-
senger compartments and any other
large masses, the following apply:
(1) Except as provided in paragraph
(c)(2) of this section, these items must
be positioned so that if they break
loose they will be unlikely to:
(i) Cause direct injury to occupants;
(ii) Penetrate fuel tanks or lines or
cause fire or explosion hazard by dam-
age to adjacent systems; or
(iii) Nullify any of the escape facili-
ties provided for use after an emer-
gency landing.
(2) When such positioning is not prac-
tical (e.g. fuselage mounted engines or
auxiliary power units) each such item
of mass shall be restrained under all
loads up to those specified in paragraph
(b)(3) of this section. The local attach-
ments for these items should be de-
signed to withstand 1.33 times the spec-
ified loads if these items are subject to
severe wear and tear through frequent
removal (e.g. quick change interior
items).
(d) Seats and items of mass (and
their supporting structure) must not
deform under any loads up to those
specified in paragraph (b)(3) of this sec-
tion in any manner that would impede
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