title-14-part-27-sec27-573

509

Federal Aviation Administration, DOT

§ 27.573

paragraph (b)(1) of this section. In addi-
tion, each float must be designed for
combined vertical and drag loads using
a relative limit speed of 20 knots be-
tween the rotorcraft and the water.
The vertical load may not be less than
the highest likely buoyancy load deter-
mined under paragraph (b)(1) of this
section.

[Amdt. 27–26, 55 FR 8000, Mar. 6, 1990]

ATIGUE

VALUATION

§ 27.571

Fatigue evaluation of flight

structure.

(a)

General. Each portion of the flight

structure (the flight structure includes
rotors, rotor drive systems between the
engines and the rotor hubs, controls,
fuselage, landing gear, and their re-
lated primary attachments), the failure
of which could be catastrophic, must be
identified and must be evaluated under
paragraph (b), (c), (d), or (e) of this sec-
tion. The following apply to each fa-
tigue evaluation:

(1) The procedure for the evaluation

must be approved.

(2) The locations of probable failure

must be determined.

(3) Inflight measurement must be in-

cluded in determining the following:

(i) Loads or stresses in all critical

conditions throughout the range of
limitations in § 27.309, except that ma-
neuvering load factors need not exceed
the maximum values expected in oper-
ation.

(ii) The effect of altitude upon these

loads or stresses.

(4) The loading spectra must be as se-

vere as those expected in operation in-
cluding, but not limited to, external
cargo operations, if applicable, and
ground-air-ground cycles. The loading
spectra must be based on loads or
stresses determined under paragraph
(a)(3) of this section.

(b)

Fatigue tolerance evaluation. It

must be shown that the fatigue toler-
ance of the structure ensures that the
probability of catastrophic fatigue fail-
ure is extremely remote without estab-
lishing replacement times, inspection
intervals or other procedures under
section A27.4 of appendix A.

(c)

Replacement time evaluation. it

must be shown that the probability of
catastrophic fatigue failure is ex-

tremely remote within a replacement
time furnished under section A27.4 of
appendix A.

(d)

Fail-safe evaluation. The following

apply to fail-safe evaluation:

(1) It must be shown that all partial

failures will become readily detectable
under inspection procedures furnished
under section A27.4 of appendix A.

(2) The interval between the time

when any partial failure becomes read-
ily detectable under paragraph (d)(1) of
this section, and the time when any
such failure is expected to reduce the
remaining strength of the structure to
limit or maximum attainable loads
(whichever is less), must be deter-
mined.

(3) It must be shown that the interval

determined under paragraph (d)(2) of
this section is long enough, in relation
to the inspection intervals and related
procedures furnished under section
A27.4 of appendix A, to provide a prob-
ability of detection great enough to en-
sure that the probability of cata-
strophic failure is extremely remote.

(e)

Combination of replacement time

and failsafe evaluations. A component
may be evaluated under a combination
of paragraphs (c) and (d) of this sec-
tion. For such component it must be
shown that the probability of cata-
strophic failure is extremely remote
with an approved combination of re-
placement time, inspection intervals,
and related procedures furnished under
section A27.4 of appendix A.

(Secs. 313(a), 601, 603, 604, and 605, 72 Stat. 752,
775, and 778, (49 U.S.C. 1354(a), 1421, 1423, 1424,
and 1425; sec. 6(c), 49 U.S.C. 1655(c)))

[Amdt. 27–3, 33 FR 14106, Sept. 18, 1968, as
amended by Amdt. 27–12, 42 FR 15044, Mar. 17,
1977; Amdt. 27–18, 45 FR 60177, Sept. 11, 1980;
Amdt. 27–26, 55 FR 8000, Mar. 6, 1990]

§ 27.573

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

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14 CFR Ch. I (1–1–24 Edition)

§ 27.573

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 § 27.309 (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 § 27.1529.

(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

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511

Federal Aviation Administration, DOT

§ 27.603

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 § 27.1529.

[Doc. No. FAA–2009–0660, Amdt. 27–47, 76 FR
74663, Dec. 1, 2011]

Subpart D—Design and

Construction

ENERAL

§ 27.601

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.

§ 27.602

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 characteristics
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]

§ 27.603

Materials.

The suitability and durability of ma-

terials used for parts, the failure of
which could adversely affect safety,
must—

(a) Be established on the basis of ex-

perience or tests;

(b) Meet approved specifications that

ensure their having the strength and
other properties assumed in the design
data; and

environmental conditions, such as tem-
perature and humidity, expected in
service.

(Secs. 313(a), 601, 603, 604, Federal Aviation
Act of 1958 (49 U.S.C. 1354(a), 1421, 1423, 1424);
and sec. 6(c) of the Dept. of Transportation
Act (49 U.S.C. 1655(c)))

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–11, 41 FR 55469, Dec. 20,
1976; Amdt. 27–16, 43 FR 50599, Oct. 30, 1978]

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