Code of Federal Regulations - Title 14

659

Federal Aviation Administration, DOT

§ 27.573

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

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; and

(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
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]

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