603 

Federal Aviation Administration, DOT 

§ 29.621 

§ 29.611

Inspection provisions. 

There must be means to allow close 

examination of each part that re-
quires— 

(a) Recurring inspection; 
(b) Adjustment for proper alignment 

and functioning; or 

(c) Lubrication. 

§ 29.613

Material strength properties 

and design values. 

(a) Material strength properties must 

be based on enough tests of material 
meeting specifications to establish de-
sign values on a statistical basis. 

(b) Design values must be chosen to 

minimize the probability of structural 
failure due to material variability. Ex-
cept as provided in paragraphs (d) and 
(e) of this section, compliance with 
this paragraph must be shown by se-
lecting design values that assure mate-
rial strength with the following prob-
ability— 

(1) Where applied loads are eventu-

ally distributed through a single mem-
ber within an assembly, the failure of 
which would result in loss of structural 
integrity of the component, 99 percent 
probability with 95 percent confidence; 
and 

(2) For redundant structures, those in 

which the failure of individual ele-
ments would result in applied loads 
being safely distributed to other load- 
carrying members, 90 percent prob-
ability with 95 percent confidence. 

(c) The strength, detail design, and 

fabrication of the structure must mini-
mize the probability of disastrous fa-
tigue failure, particularly at points of 
stress concentration. 

(d) Design values may be those con-

tained in the following publications 
(available from the Naval Publications 
and Forms Center, 5801 Tabor Avenue, 
Philadelphia, PA 19120) or other values 
approved by the Administrator: 

(1) MIL—HDBK–5, ‘‘Metallic Mate-

rials and Elements for Flight Vehicle 
Structure’’. 

(2) MIL—HDBK–17, ‘‘Plastics for 

Flight Vehicles’’. 

(3) ANC–18, ‘‘Design of Wood Aircraft 

Structures’’. 

(4) MIL—HDBK–23, ‘‘Composite Con-

struction for Flight Vehicles’’. 

(e) Other design values may be used if 

a selection of the material is made in 

which a specimen of each individual 
item is tested before use and it is de-
termined that the actual strength 
properties of that particular item will 
equal or exceed those used in design. 

(Secs. 313(a), 601, 603, 604, Federal Aviation 
Act of 1958 (49 U.S.C. 1354(a), 1421, 1423, 1424), 
sec. 6(c), Dept. of Transportation Act (49 
U.S.C. 1655(c))) 

[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as 
amended by Amdt. 29–17, 43 FR 50599, Oct. 30, 
1978; Amdt. 29–30, 55 FR 8003, Mar. 6, 1990] 

§ 29.619

Special factors. 

(a) The special factors prescribed in 

§§ 29.621 through 29.625 apply to each 
part of the structure whose strength 
is— 

(1) Uncertain; 
(2) Likely to deteriorate in service 

before normal replacement; or 

(3) Subject to appreciable variability 

due to— 

(i) Uncertainties in manufacturing 

processes; or 

(ii) Uncertainties in inspection meth-

ods. 

(b) For each part of the rotorcraft to 

which §§ 29.621 through 29.625 apply, the 
factor of safety prescribed in § 29.303 
must be multiplied by a special factor 
equal to— 

(1) The applicable special factors pre-

scribed in §§ 29.621 through 29.625; or 

(2) Any other factor great enough to 

ensure that the probability of the part 
being understrength because of the un-
certainties specified in paragraph (a) of 
this section is extremely remote. 

§ 29.621

Casting factors. 

(a) 

General. The factors, tests, and in-

spections specified in paragraphs (b) 
and (c) of this section must be applied 
in addition to those necessary to estab-
lish foundry quality control. The in-
spections must meet approved speci-
fications. Paragraphs (c) and (d) of this 
section apply to structural castings ex-
cept castings that are pressure tested 
as parts of hydraulic or other fluid sys-
tems and do not support structural 
loads. 

(b) 

Bearing stresses and surfaces. The 

casting factors specified in paragraphs 
(c) and (d) of this section— 

(1) Need not exceed 1.25 with respect 

to bearing stresses regardless of the 
method of inspection used; and 

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