Federal Aviation Administration, DOT

Section 29.573

(h) Based on the requirements of this
section, inspections and retirement
times or approved equivalent means
must be established to avoid catastrophic failure. The inspections and
retirement times or approved equivalent means must be included in the
Airworthiness Limitations Section of
the Instructions for Continued Airworthiness required by Section 29.1529
and Section A29.4 of Appendix A of this
part.
(i) If inspections for any of the damage types identified in paragraph (e)(4)
of this section cannot be established
within the limitations of geometry,
inspectability, or good design practice,
then supplemental procedures, in conjunction with the PSE retirement
time, must be established to minimize
the risk of occurrence of these types of
damage that could result in a catastrophic failure during the operational
life of the rotorcraft.
[Doc. No. FAA-2009-0413, Amdt. 29-55, 76 FR
75442, Dec. 2, 2011]

spaschal on DSK3GDR082PROD with CFR

Section 29.573 Damage Tolerance and Fatigue Evaluation of Composite
Rotorcraft Structures.
(a) Each applicant must evaluate the
composite rotorcraft structure under
the damage tolerance standards of
paragraph (d) of this section unless the
applicant establishes that a damage
tolerance evaluation is impractical
within
the
limits
of
geometry,
inspectability, and good design practice. If an applicant establishes that it
is impractical within the limits of geometry, inspectability, and good design
practice, the applicant must do a fatigue evaluation in accordance with
paragraph (e) of this section.
(b) The methodology used to establish compliance with this section must
be submitted to and approved by the
Administrator.
(c) Definitions:
(1) Catastrophic failure is an event
that could prevent continued safe
flight and landing.
(2) Principal Structural Elements (PSEs)
are structural elements that contribute significantly to the carrying of
flight or ground loads, the failure of
which could result in catastrophic failure of the rotorcraft.

(3) Threat Assessment is an assessment
that specifies the locations, types, and
sizes of damage, considering fatigue,
environmental effects, intrinsic and
discrete flaws, and impact or other accidental damage (including the discrete
source of the accidental damage) that
may occur during manufacture or operation.
(d) Damage Tolerance Evaluation:
(1) Each applicant must show that
catastrophic failure due to static and
fatigue loads, considering the intrinsic
or discrete manufacturing defects or
accidental damage, is avoided throughout the operational life or prescribed
inspection intervals of the rotorcraft
by performing damage tolerance evaluations of the strength of composite
PSEs and other parts, detail design
points, and fabrication techniques.
Each applicant must account for the
effects of material and process variability along with environmental conditions in the strength and fatigue evaluations. Each applicant must evaluate
parts that include PSEs of the airframe, main and tail rotor drive systems, main and tail rotor blades and
hubs, rotor controls, fixed and movable
control surfaces, engine and transmission mountings, landing gear, other
parts, detail design points, and fabrication techniques deemed critical by the
FAA. Each damage tolerance evaluation must include:
(i) The identification of all PSEs;
(ii) In-flight and ground measurements for determining the loads or
stresses for all PSEs for all critical
conditions throughout the range of
limits in Section 29.309 (including altitude effects), except that maneuvering load
factors need not exceed the maximum
values expected in service;
(iii) The loading spectra as severe as
those expected in service based on
loads or stresses determined under
paragraph (d)(1)(ii) of this section, including external load operations, if applicable, and other operations including high-torque events;
(iv) A threat assessment for all PSEs
that specifies the locations, types, and
sizes of damage, considering fatigue,
environmental effects, intrinsic and
discrete flaws, and impact or other accidental damage (including the discrete
source of the accidental damage) that

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