spaschal on DSK3GDR082PROD with CFR

Section 25.571

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

such that this type of damage could
occur. An LOV must be established
that corresponds to the period of time,
stated as a number of total accumulated flight cycles or flight hours or
both, during which it is demonstrated
that widespread fatigue damage will
not occur in the airplane structure.
This demonstration must be by fullscale fatigue test evidence. The type
certificate may be issued prior to completion of full-scale fatigue testing,
provided the Administrator has approved a plan for completing the required tests. In that case, the Airworthiness Limitations section of the
Instructions for Continued Airworthiness required by Section 25.1529 must specify
that no airplane may be operated beyond a number of cycles equal to 1-2 the
number of cycles accumulated on the
fatigue test article, until such testing
is completed. The extent of damage for
residual strength evaluation at any
time within the operational life of the
airplane must be consistent with the
initial detectability and subsequent
growth under repeated loads. The residual strength evaluation must show
that the remaining structure is able to
withstand loads (considered as static
ultimate loads) corresponding to the
following conditions:
(1) The limit symmetrical maneuvering conditions specified in Section 25.337 at
all speeds up to Vc and in Section 25.345.
(2) The limit gust conditions specified in Section 25.341 at the specified speeds up
to VC and in Section 25.345.
(3) The limit rolling conditions specified in Section 25.349 and the limit unsymmetrical conditions specified in SectionSection 25.367
and 25.427 (a) through (c), at speeds up
to VC.
(4) The limit yaw maneuvering conditions specified in Section 25.351(a) at the specified speeds up to VC.
(5) For pressurized cabins, the following conditions:
(i) The normal operating differential
pressure combined with the expected
external aerodynamic pressures applied
simultaneously with the flight loading
conditions specified in paragraphs
(b)(1) through (4) of this section, if they
have a significant effect.
(ii) The maximum value of normal
operating differential pressure (including the expected external aerodynamic

pressures during 1 g level flight) multiplied by a factor of 1.15, omitting other
loads.
(6) For landing gear and directly-affected airframe structure, the limit
ground loading conditions specified in
SectionSection 25.473, 25.491, and 25.493.
If significant changes in structural
stiffness or geometry, or both, follow
from a structural failure, or partial
failure, the effect on damage tolerance
must be further investigated.
(c) Fatigue (safe-life) evaluation. Compliance with the damage-tolerance requirements of paragraph (b) of this section is not required if the applicant establishes that their application for particular structure is impractical. This
structure must be shown by analysis,
supported by test evidence, to be able
to withstand the repeated loads of variable magnitude expected during its
service life without detectable cracks.
Appropriate safe-life scatter factors
must be applied.
(d) Sonic fatigue strength. It must be
shown by analysis, supported by test
evidence, or by the service history of
airplanes of similar structural design
and sonic excitation environment,
that - 
(1) Sonic fatigue cracks are not probable in any part of the flight structure
subject to sonic excitation; or
(2) Catastrophic failure caused by
sonic cracks is not probable assuming
that the loads prescribed in paragraph
(b) of this section are applied to all
areas affected by those cracks.
(e) Damage-tolerance (discrete source)
evaluation. The airplane must be capable of successfully completing a flight
during which likely structural damage
occurs as a result of - 
(1) Impact with a 4-pound bird when
the velocity of the airplane relative to
the bird along the airplane-s flight
path is equal to Vc at sea level or 0.85Vc
at 8,000 feet, whichever is more critical;
(2) Uncontained fan blade impact;
(3) Uncontained engine failure; or
(4) Uncontained high energy rotating
machinery failure.
The damaged structure must be able to
withstand the static loads (considered
as ultimate loads) which are reasonably expected to occur on the flight.
Dynamic effects on these static loads

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