657 

Federal Aviation Administration, DOT 

§ 27.571 

for ditching must meet the require-
ments of this section and § 27.801(e). 

(a) 

Forward speed landing conditions. 

The rotorcraft must initially contact 
the most critical wave for reasonably 
probable water conditions at forward 
velocities from zero up to 30 knots in 
likely pitch, roll, and yaw attitudes. 
The rotorcraft limit vertical descent 
velocity may not be less than 5 feet per 
second relative to the mean water sur-
face. Rotor lift may be used to act 
through the center of gravity through-
out the landing impact. This lift may 
not exceed two-thirds of the design 
maximum weight. A maximum forward 
velocity of less than 30 knots may be 
used in design if it can be dem-
onstrated that the forward velocity se-
lected would not be exceeded in a nor-
mal one-engine-out touchdown. 

(b) 

Auxiliary or emergency float condi-

tions—(1)  Floats fixed or deployed before 
initial water contact. In addition to the 
landing loads in paragraph (a) of this 
section, each auxiliary or emergency 
float, of its support and attaching 
structure in the airframe or fuselage, 
must be designed for the load devel-
oped by a fully immersed float unless it 
can be shown that full immersion is 
unlikely. If full immersion is unlikely, 
the highest likely float buoyancy load 
must be applied. The highest likely 
buoyancy load must include consider-
ation of a partially immersed float cre-
ating restoring moments to com-
pensate the upsetting moments caused 
by side wind, unsymmetrical rotorcraft 
loading, water wave action, rotorcraft 
inertia, and probable structural dam-
age and leakage considered under 
§ 27.801(d). Maximum roll and pitch an-
gles determined from compliance with 
§ 27.801(d) may be used, if significant, to 
determine the extent of immersion of 
each float. If the floats are deployed in 
flight, appropriate air loads derived 
from the flight limitations with the 
floats deployed shall be used in sub-
stantiation of the floats and their at-
tachment to the rotorcraft. For this 
purpose, the design airspeed for limit 
load is the float deployed airspeed op-
erating limit multiplied by 1.11. 

(2) 

Floats deployed after initial water 

contact. Each float must be designed for 
full or partial immersion perscribed in 
paragraph (b)(1) of this section. In addi-

tion, each float must be designed for 
combined vertical and drag loads using 
a relative limit speed of 20 knots be-
tween the rotorcraft and the water. 
The vertical load may not be less than 
the highest likely buoyancy load deter-
mined under paragraph (b)(1) of this 
section. 

[Amdt. 27–26, 55 FR 8000, Mar. 6, 1990] 

F

ATIGUE

E

VALUATION

 

§ 27.571

Fatigue evaluation of flight 

structure. 

(a) 

General. Each portion of the flight 

structure (the flight structure includes 
rotors, rotor drive systems between the 
engines and the rotor hubs, controls, 
fuselage, landing gear, and their re-
lated primary attachments), the failure 
of which could be catastrophic, must be 
identified and must be evaluated under 
paragraph (b), (c), (d), or (e) of this sec-
tion. The following apply to each fa-
tigue evaluation: 

(1) The procedure for the evaluation 

must be approved. 

(2) The locations of probable failure 

must be determined. 

(3) Inflight measurement must be in-

cluded in determining the following: 

(i) Loads or stresses in all critical 

conditions throughout the range of 
limitations in § 27.309, except that ma-
neuvering load factors need not exceed 
the maximum values expected in oper-
ation. 

(ii) The effect of altitude upon these 

loads or stresses. 

(4) The loading spectra must be as se-

vere as those expected in operation in-
cluding, but not limited to, external 
cargo operations, if applicable, and 
ground-air-ground cycles. The loading 
spectra must be based on loads or 
stresses determined under paragraph 
(a)(3) of this section. 

(b) 

Fatigue tolerance evaluation. It 

must be shown that the fatigue toler-
ance of the structure ensures that the 
probability of catastrophic fatigue fail-
ure is extremely remote without estab-
lishing replacement times, inspection 
intervals or other procedures under 
section A27.4 of appendix A. 

(c) 

Replacement time evaluation. it 

must be shown that the probability of 
catastrophic fatigue failure is ex-
tremely remote within a replacement 

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