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 

(C) Whether the inspection will de-

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 

G

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 

(c) Take into account the effects of 

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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