235 

Federal Aviation Administration, DOT 

§ 23.574 

(2) The growth rate or no-growth of 

damage that may occur from fatigue, 
corrosion, manufacturing flaws or im-
pact damage, under repeated loads ex-
pected in service, must be established 
by tests or analysis supported by tests. 

(3) The structure must be shown by 

residual strength tests, or analysis sup-
ported by residual strength tests, to be 
able to withstand critical limit flight 
loads, considered as ultimate loads, 
with the extent of detectable damage 
consistent with the results of the dam-
age tolerance evaluations. For pressur-
ized cabins, the following loads must be 
withstood: 

(i) Critical limit flight loads with the 

combined effects of normal operating 
pressure and expected external aero-
dynamic pressures. 

(ii) The expected external aero-

dynamic pressures in 1g flight com-
bined with a cabin differential pressure 
equal to 1.1 times the normal operating 
differential pressure without any other 
load. 

(4) The damage growth, between ini-

tial detectability and the value se-
lected for residual strength demonstra-
tions, factored to obtain inspection in-
tervals, must allow development of an 
inspection program suitable for appli-
cation by operation and maintenance 
personnel. 

(5) For any bonded joint, the failure 

of which would result in catastrophic 
loss of the airplane, the limit load ca-
pacity must be substantiated by one of 
the following methods— 

(i) The maximum disbonds of each 

bonded joint consistent with the capa-
bility to withstand the loads in para-
graph (a)(3) of this section must be de-
termined by analysis, tests, or both. 
Disbonds of each bonded joint greater 
than this must be prevented by design 
features; or 

(ii) Proof testing must be conducted 

on each production article that will 
apply the critical limit design load to 
each critical bonded joint; or 

(iii) Repeatable and reliable non-de-

structive inspection techniques must 
be established that ensure the strength 
of each joint. 

(6) Structural components for which 

the damage tolerance method is shown 
to be impractical must be shown by 
component fatigue tests, or analysis 

supported by tests, to be able to with-
stand the repeated loads of variable 
magnitude expected in service. Suffi-
cient component, subcomponent, ele-
ment, or coupon tests must be done to 
establish the fatigue scatter factor and 
the environmental effects. Damage up 
to the threshold of detectability and 
ultimate load residual strength capa-
bility must be considered in the dem-
onstration. 

(b) 

Metallic airframe structure. If the 

applicant elects to use § 23.571(c) or 
§ 23.572(a)(3), then the damage tolerance 
evaluation must include a determina-
tion of the probable locations and 
modes of damage due to fatigue, corro-
sion, or accidental damage. Damage at 
multiple sites due to fatigue must be 
included where the design is such that 
this type of damage can be expected to 
occur. The evaluation must incor-
porate repeated load and static anal-
yses supported by test evidence. The 
extent of damage for residual strength 
evaluation at any time within the 
operational life of the airplane must be 
consistent with the initial detect-
ability and subsequent growth under 
repeated loads. The residual strength 
evaluation must show that the remain-
ing structure is able to withstand crit-
ical limit flight loads, considered as ul-
timate, with the extent of detectable 
damage consistent with the results of 
the damage tolerance evaluations. For 
pressurized cabins, the following load 
must be withstood: 

(1) The normal operating differential 

pressure combined with the expected 
external aerodynamic pressures applied 
simultaneously with the flight loading 
conditions specified in this part, and 

(2) The expected external aero-

dynamic pressures in 1g flight com-
bined with a cabin differential pressure 
equal to 1.1 times the normal operating 
differential pressure without any other 
load. 

[Doc. No. 26269, 58 FR 42163, Aug. 6, 1993; 58 
FR 51970, Oct. 5, 1993, as amended by Amdt. 
23–48, 61 FR 5147, Feb. 9, 1996; 73 FR 19746, 
Apr. 11, 2008] 

§ 23.574

Metallic damage tolerance and 

fatigue evaluation of commuter cat-
egory airplanes. 

For commuter category airplanes— 

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