234 

14 CFR Ch. I (1–1–14 Edition) 

§ 23.572 

failure, or obvious partial failure, of a 
principal structural element, and that 
the remaining structures are able to 
withstand a static ultimate load factor 
of 75 percent of the limit load factor at 
V

C,

considering the combined effects of 

normal operating pressures, expected 
external aerodynamic pressures, and 
flight loads. These loads must be mul-
tiplied by a factor of 1.15 unless the dy-
namic effects of failure under static 
load are otherwise considered. 

(c) The damage tolerance evaluation 

of § 23.573(b). 

(d) If certification for operation 

above 41,000 feet is requested, a damage 
tolerance evaluation of the fuselage 
pressure boundary per § 23.573(b) must 
be conducted. 

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as 
amended by Amdt. 23–14, 38 FR 31821, Nov. 19, 
1973; Amdt. 23–45, 58 FR 42163, Aug. 6, 1993; 
Amdt. 23–48, 61 FR 5147, Feb. 9, 1996; Amdt. 
23–62, 76 FR 75756, Dec. 2, 2011] 

§ 23.572

Metallic wing, empennage, 

and associated structures. 

(a) For normal, utility, and acrobatic 

category airplanes, the strength, detail 
design, and fabrication of those parts 
of the airframe structure whose failure 
would be catastrophic must be evalu-
ated under one of the following unless 
it is shown that the structure, oper-
ating stress level, materials and ex-
pected uses are comparable, from a fa-
tigue standpoint, to a similar design 
that has had extensive satisfactory 
service experience: 

(1) A fatigue strength investigation 

in which the structure is shown by 
tests, or by analysis supported by test 
evidence, to be able to withstand the 
repeated loads of variable magnitude 
expected in service; or 

(2) A fail-safe strength investigation 

in which it is shown by analysis, tests, 
or both, that catastrophic failure of 
the structure is not probable after fa-
tigue failure, or obvious partial failure, 
of a principal structural element, and 
that the remaining structure is able to 
withstand a static ultimate load factor 
of 75 percent of the critical limit load 
factor at 

V

c.

These loads must be multi-

plied by a factor of 1.15 unless the dy-
namic effects of failure under static 
load are otherwise considered. 

(3) The damage tolerance evaluation 

of § 23.573(b). 

(b) Each evaluation required by this 

section must— 

(1) Include typical loading spectra 

(e.g. taxi, ground-air-ground cycles, 
maneuver, gust); 

(2) Account for any significant effects 

due to the mutual influence of aero-
dynamic surfaces; and 

(3) Consider any significant effects 

from propeller slipstream loading, and 
buffet from vortex impingements. 

[Amdt. 23–7, 34 FR 13090, Aug. 13, 1969, as 
amended by Amdt. 23–14, 38 FR 31821, Nov. 19, 
1973; Amdt. 23–34, 52 FR 1830, Jan. 15, 1987; 
Amdt. 23–38, 54 FR 39511, Sept. 26, 1989; Amdt. 
23–45, 58 FR 42163, Aug. 6, 1993; Amdt. 23–48, 61 
FR 5147, Feb. 9, 1996] 

§ 23.573

Damage tolerance and fatigue 

evaluation of structure. 

(a) 

Composite airframe structure. Com-

posite airframe structure must be eval-
uated under this paragraph instead of 
§§ 23.571 and 23.572. The applicant must 
evaluate the composite airframe struc-
ture, the failure of which would result 
in catastrophic loss of the airplane, in 
each wing (including canards, tandem 
wings, and winglets), empennage, their 
carrythrough and attaching structure, 
moveable control surfaces and their at-
taching structure fuselage, and pres-
sure cabin using the damage-tolerance 
criteria prescribed in paragraphs (a)(1) 
through (a)(4) of this section unless 
shown to be impractical. If the appli-
cant establishes that damage-tolerance 
criteria is impractical for a particular 
structure, the structure must be evalu-
ated in accordance with paragraphs 
(a)(1) and (a)(6) of this section. Where 
bonded joints are used, the structure 
must also be evaluated in accordance 
with paragraph (a)(5) of this section. 
The effects of material variability and 
environmental conditions on the 
strength and durability properties of 
the composite materials must be ac-
counted for in the evaluations required 
by this section. 

(1) It must be demonstrated by tests, 

or by analysis supported by tests, that 
the structure is capable of carrying ul-
timate load with damage up to the 
threshold of detectability considering 
the inspection procedures employed. 

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