title-14-part-29-sec29-571

599

Federal Aviation Administration, DOT

§ 29.571

the highest likely buoyancy load deter-
mined under paragraph (b)(1) of this
section.

[Amdt. 27–26, 55 FR 8003, Mar. 6, 1990]

ATIGUE

VALUATION

§ 29.571

Fatigue Tolerance Evaluation

of Metallic Structure.

(a) A fatigue tolerance evaluation of

each principal structural element
(PSE) must be performed, and appro-
priate inspections and retirement time
or approved equivalent means must be
established to avoid catastrophic fail-
ure during the operational life of the
rotorcraft. The fatigue tolerance eval-
uation must consider the effects of
both fatigue and the damage deter-
mined 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 trans-
mission 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 con-
tributes significantly to the carriage of
flight or ground loads, and the fatigue
failure of that structural element could
result in catastrophic failure of the air-
craft.

lish compliance with this section must
be submitted to and approved by the
Administrator.

(d) Considering all rotorcraft struc-

ture, structural elements, and assem-
blies, each PSE must be identified.

(e) Each fatigue tolerance evaluation

required by this section must include:

(1) In-flight measurements to deter-

mine the fatigue loads or stresses for
the PSEs identified in paragraph (d) of
this section in all critical conditions
throughout the range of design limita-
tions required by § 29.309 (including al-
titude effects), except that maneu-
vering load factors need not exceed the
maximum values expected in oper-
ations.

(2) The loading spectra as severe as

those expected in operations based on
loads or stresses determined under
paragraph (e)(1) of this section, includ-
ing external load operations, if applica-
ble, and other high frequency power-
cycle operations.

(3) Takeoff, landing, and taxi loads

when evaluating the landing gear and
other affected PSEs.

(4) For each PSE identified in para-

graph (d) of this section, a threat as-
sessment which includes a determina-
tion of the probable locations, types,
and sizes of damage, taking into ac-
count fatigue, environmental effects,
intrinsic and discrete flaws, or acci-
dental damage that may occur during
manufacture or operation.

(5) A determination of the fatigue

tolerance characteristics for the PSE
with the damage identified in para-
graph (e)(4) of this section that sup-
ports the inspection and retirement
times, or other approved equivalent
means.

(6) Analyses supported by test evi-

dence and, if available, service experi-
ence.

(f) A residual strength determination

is required that substantiates the max-
imum damage size assumed in the fa-
tigue tolerance evaluation. In deter-
mining inspection intervals based on
damage growth, the residual strength
evaluation must show that the remain-
ing structure, after damage growth, is
able to withstand design limit loads
without failure.

(g) The effect of damage on stiffness,

dynamic behavior, loads, and func-
tional performance must be considered.

(h) Based on the requirements of this

section, inspections and retirement
times or approved equivalent means
must be established to avoid cata-
strophic failure. The inspections and
retirement times or approved equiva-
lent means must be included in the
Airworthiness Limitations Section of
the Instructions for Continued Air-
worthiness required by Section 29.1529
and Section A29.4 of Appendix A of this
part.

(i) If inspections for any of the dam-

age types identified in paragraph (e)(4)
of this section cannot be established
within the limitations of geometry,
inspectability, or good design practice,

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14 CFR Ch. I (1–1–24 Edition)

§ 29.573

then supplemental procedures, in con-
junction with the PSE retirement
time, must be established to minimize
the risk of occurrence of these types of
damage that could result in a cata-
strophic failure during the operational
life of the rotorcraft.

[Doc. No. FAA–2009–0413, Amdt. 29–55, 76 FR
75442, Dec. 2, 2011]

§ 29.573

Damage Tolerance and Fa-

tigue 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 prac-
tice. If an applicant establishes that it
is impractical within the limits of ge-
ometry, inspectability, and good design
practice, the applicant must do a fa-
tigue evaluation in accordance with
paragraph (e) of this section.

(b) The methodology used to estab-

lish compliance with this section must
be submitted to and approved by the
Administrator.

Catastrophic failure is an event

that could prevent continued safe
flight and landing.

(2)

Principal Structural Elements (PSEs)

are structural elements that con-
tribute significantly to the carrying of
flight or ground loads, the failure of
which could result in catastrophic fail-
ure 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 ac-
cidental damage (including the discrete
source of the accidental damage) that
may occur during manufacture or oper-
ation.

(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 through-
out the operational life or prescribed
inspection intervals of the rotorcraft
by performing damage tolerance eval-

uations 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 varia-
bility along with environmental condi-
tions in the strength and fatigue eval-
uations. Each applicant must evaluate
parts that include PSEs of the air-
frame, main and tail rotor drive sys-
tems, main and tail rotor blades and
hubs, rotor controls, fixed and movable
control surfaces, engine and trans-
mission mountings, landing gear, other
parts, detail design points, and fabrica-
tion techniques deemed critical by the
FAA. Each damage tolerance evalua-
tion must include:

(i) The identification of all PSEs;
(ii) In-flight and ground measure-

ments for determining the loads or
stresses for all PSEs for all critical
conditions throughout the range of
limits in § 29.309 (including altitude ef-
fects), 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, in-
cluding external load operations, if ap-
plicable, and other operations includ-
ing high-torque events;

(iv) A threat assessment for all PSEs

(v) An assessment of the residual

strength and fatigue characteristics of
all PSEs that supports the replacement
times and inspection intervals estab-
lished under paragraph (d)(2) of this
section.

(2) Each applicant must establish re-

placement times, inspections, or other
procedures for all PSEs to require the
repair or replacement of damaged parts
before a catastrophic failure. These re-
placement times, inspections, or other
procedures must be included in the Air-
worthiness Limitations Section of the
Instructions for Continued Airworthi-
ness required by § 29.1529.