background image

513 

Federal Aviation Administration, DOT 

§ 27.621 

(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 structure, 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, Pennsylvania 19120) or 
other values approved by the Adminis-
trator: 

(1) MIL-HDBK-5, ‘‘Metallic Materials 

and Elements for Flight Vehicle Struc-
ture’’. 

(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. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–16, 43 FR 50599, Oct. 30, 
1978; Amdt. 27–26, 55 FR 8000, Mar. 6, 1990] 

§ 27.619

Special factors. 

(a) The special factors prescribed in 

§§ 27.621 through 27.625 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 to which §§ 27.621 

through 27.625 apply, the factor of safe-
ty prescribed in § 27.303 must be multi-
plied by a special factor equal to— 

(1) The applicable special factors pre-

scribed in §§ 27.621 through 27.625; 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. 

§ 27.621

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 

(2) Need not be used with respect to 

the bearing surfaces of a part whose 
bearing factor is larger than the appli-
cable casting factor. 

(c) 

Critical castings. For each casting 

whose failure would preclude continued 
safe flight and landing of the rotorcraft 
or result in serious injury to any occu-
pant, the following apply: 

(1) Each critical casting must— 
(i) Have a casting factor of not less 

than 1.25; and 

(ii) Receive 100 percent inspection by 

visual, radiographic, and magnetic par-
ticle (for ferromagnetic materials) or 
penetrant (for nonferromagnetic mate-
rials) inspection methods or approved 
equivalent inspection methods. 

(2) For each critical casting with a 

casting factor less than 1.50, three sam-
ple castings must be static tested and 
shown to meet— 

VerDate Sep<11>2014 

09:06 Jun 28, 2024

Jkt 262046

PO 00000

Frm 00523

Fmt 8010

Sfmt 8010

Y:\SGML\262046.XXX

262046

jspears on DSK121TN23PROD with CFR