599 

Federal Aviation Administration, DOT 

§ 29.573 

(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, 
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. 

(c) Definitions: 
(1) 

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 

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 

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