title-14-part-29-sec29-573

600

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.

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Federal Aviation Administration, DOT

§ 29.602

(i) Replacement times for PSEs must

be determined by tests, or by analysis
supported by tests, and must show that
the structure is able to withstand the
repeated loads of variable magnitude
expected in-service. In establishing
these replacement times, the following
items must be considered:

(A) Damage identified in the threat

assessment required by paragraph
(d)(1)(iv) of this section;

(B) Maximum acceptable manufac-

turing defects and in-service damage
(

i.e., those that do not lower the resid-

ual strength below ultimate design
loads and those that can be repaired to
restore ultimate strength); and

after applying repeated loads.

(ii) Inspection intervals for PSEs

must be established to reveal any dam-
age identified in the threat assessment
required by paragraph (d)(1)(iv) of this
section that may occur from fatigue or
other in-service causes before such
damage has grown to the extent that
the component cannot sustain the re-
quired residual strength capability. In
establishing these inspection intervals,
the following items must be consid-
ered:

(A) The growth rate, including no-

growth, of the damage under the re-
peated loads expected in-service deter-
mined by tests or analysis supported
by tests;

(B) The required residual strength for

the assumed damage established after
considering the damage type, inspec-
tion interval, detectability of damage,
and the techniques adopted for damage
detection. The minimum required re-
sidual strength is limit load; and

tect the damage growth before the
minimum residual strength is reached
and restored to ultimate load capa-
bility, or whether the component will
require replacement.

(3) Each applicant must consider the

effects of damage on stiffness, dynamic
behavior, loads, and functional per-
formance on all PSEs when substan-
tiating the maximum assumed damage
size and inspection interval.

(e) Fatigue Evaluation: If an appli-

cant establishes that the damage toler-
ance evaluation described in paragraph
(d) of this section is impractical within

the limits of geometry, inspectability,
or good design practice, the applicant
must do a fatigue evaluation of the
particular composite rotorcraft struc-
ture and:

(1) Identify all PSEs considered in

the fatigue evaluation;

(2) Identify the types of damage for

all PSEs considered in the fatigue eval-
uation;

(3) Establish supplemental proce-

dures to minimize the risk of cata-
strophic failure associated with the
damages identified in paragraph (d) of
this section; and

(4) Include these supplemental proce-

dures in the Airworthiness Limitations
section of the Instructions for Contin-
ued Airworthiness required by § 29.1529.

[Doc. No. FAA–2009–0660, Amdt. 29–59, 76 FR
74664, Dec. 1, 2011]

Subpart D—Design and

Construction

ENERAL

§ 29.601

Design.

(a) The rotorcraft may have no de-

sign features or details that experience
has shown to be hazardous or unreli-
able.

(b) The suitability of each question-

able design detail and part must be es-
tablished by tests.

§ 29.602

Critical parts.

(a)

Critical part. A critical part is a

part, the failure of which could have a
catastrophic effect upon the rotocraft,
and for which critical characterists
have been identified which must be
controlled to ensure the required level
of integrity.

(b) If the type design includes critical

parts, a critical parts list shall be es-
tablished. Procedures shall be estab-
lished to define the critical design
characteristics, identify processes that
affect those characteristics, and iden-
tify the design change and process
change controls necessary for showing
compliance with the quality assurance
requirements of part 21 of this chapter.

[Doc. No. 29311, 64 FR 46232, Aug. 24, 1999]