Section 29.571

14 CFR Ch. I (1-1-19 Edition)

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 substantiation of the floats and their attachment to the rotorcraft. For this
purpose, the design airspeed for limit
load is the float deployed airspeed operating limit multiplied by 1.11.
(2) Floats deployed after initial water
contact. Each float must be designed for
full or partial immersion prescribed in
paragraph (b)(1) of this section. In addition, each float must be designed for
combined vertical and drag loads using
a relative limit speed of 20 knots between the rotorcraft and the water.
The vertical load may not be less than
the highest likely buoyancy load determined under paragraph (b)(1) of this
section.
[Amdt. 27-26, 55 FR 8003, Mar. 6, 1990]

spaschal on DSK3GDR082PROD with CFR

FATIGUE EVALUATION
Section 29.571 Fatigue Tolerance Evaluation
of Metallic Structure.
(a) A fatigue tolerance evaluation of
each principal structural element
(PSE) must be performed, and appropriate inspections and retirement time
or approved equivalent means must be
established to avoid catastrophic failure during the operational life of the
rotorcraft. The fatigue tolerance evaluation must consider the effects of
both fatigue and the damage determined under paragraph (e)(4) of this
section. Parts to be evaluated include
PSEs of the rotors, rotor drive systems
between the engines and rotor hubs,
controls, fuselage, fixed and movable
control surfaces, engine and transmission mountings, landing gear, and
their related primary attachments.
(b) For the purposes of this section,
the term - 
(1) Catastrophic failure means an
event that could prevent continued
safe flight and landing.
(2) Principal structural element (PSE)
means a structural element that contributes significantly to the carriage of
flight or ground loads, and the fatigue
failure of that structural element could
result in catastrophic failure of the aircraft.
(c) The methodology used to establish compliance with this section must

be submitted to and approved by the
Administrator.
(d) Considering all rotorcraft structure, structural elements, and assemblies, each PSE must be identified.
(e) Each fatigue tolerance evaluation
required by this section must include:
(1) In-flight measurements to determine the fatigue loads or stresses for
the PSEs identified in paragraph (d) of
this section in all critical conditions
throughout the range of design limitations required by Section 29.309 (including altitude effects), except that maneuvering load factors need not exceed the
maximum values expected in operations.
(2) The loading spectra as severe as
those expected in operations based on
loads or stresses determined under
paragraph (e)(1) of this section, including external load operations, if applicable, and other high frequency powercycle operations.
(3) Takeoff, landing, and taxi loads
when evaluating the landing gear and
other affected PSEs.
(4) For each PSE identified in paragraph (d) of this section, a threat assessment which includes a determination of the probable locations, types,
and sizes of damage, taking into account fatigue, environmental effects,
intrinsic and discrete flaws, or accidental damage that may occur during
manufacture or operation.
(5) A determination of the fatigue
tolerance characteristics for the PSE
with the damage identified in paragraph (e)(4) of this section that supports the inspection and retirement
times, or other approved equivalent
means.
(6) Analyses supported by test evidence and, if available, service experience.
(f) A residual strength determination
is required that substantiates the maximum damage size assumed in the fatigue tolerance evaluation. In determining inspection intervals based on
damage growth, the residual strength
evaluation must show that the remaining structure, after damage growth, is
able to withstand design limit loads
without failure.
(g) The effect of damage on stiffness,
dynamic behavior, loads, and functional performance must be considered.

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