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264 

14 CFR Ch. I (1–1–24 Edition) 

§ 25.619 

structural failures due to material var-
iability. Except as provided in para-
graphs (e) and (f) of this section, com-
pliance must be shown by selecting ma-
terial design values which 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. 

(2) For redundant structure, in which 

the failure of individual elements 
would result in applied loads being 
safely distributed to other load car-
rying members, 90 percent probability 
with 95 percent confidence. 

(c) The effects of environmental con-

ditions, such as temperature and mois-
ture, on material design values used in 
an essential component or structure 
must be considered where these effects 
are significant within the airplane op-
erating envelope. 

(d) [Reserved] 
(e) Greater material design values 

may be used if a ‘‘premium selection’’ 
of the material is made in which a 
specimen of each individual item is 
tested before use to determine that the 
actual strength properties of that par-
ticular item will equal or exceed those 
used in design. 

(f) Other material design values may 

be used if approved by the Adminis-
trator. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–46, 43 FR 50595, Oct. 30, 
1978; Amdt. 25–72, 55 FR 29776, July 20, 1990; 
Amdt. 25–112, 68 FR 46431, Aug. 5, 2003] 

§ 25.619

Special factors. 

The factor of safety prescribed in 

§ 25.303 must be multiplied by the high-
est pertinent special factor of safety 
prescribed in §§ 25.621 through 25.625 for 
each part of the structure whose 
strength is— 

(a) Uncertain; 
(b) Likely to deteriorate in service 

before normal replacement; or 

(c) Subject to appreciable variability 

because of uncertainties in manufac-
turing processes or inspection methods. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5674, Apr. 8, 
1970] 

§ 25.621

Casting factors. 

(a) 

General.  For castings used in 

structural applications, the factors, 
tests, and inspections specified in para-
graphs (b) through (d) of this section 
must be applied in addition to those 
necessary to establish foundry quality 
control. The inspections must meet ap-
proved specifications. Paragraphs (c) 
and (d) of this section apply to any 
structural castings, except castings 
that are pressure tested as parts of hy-
draulic or other fluid systems 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. Each casting 

whose failure could preclude continued 
safe flight and landing of the airplane 
or could result in serious injury to oc-
cupants is a critical casting. Each crit-
ical casting must have a factor associ-
ated with it for showing compliance 
with strength and deformation require-
ments of § 25.305, and must comply with 
the following criteria associated with 
that factor: 

(1) A casting factor of 1.0 or greater 

may be used, provided that— 

(i) It is demonstrated, in the form of 

process qualification, proof of product, 
and process monitoring that, for each 
casting design and part number, the 
castings produced by each foundry and 
process combination have coefficients 
of variation of the material properties 
that are equivalent to those of wrought 
alloy products of similar composition. 
Process monitoring must include test-
ing of coupons cut from the prolonga-
tions of each casting (or each set of 
castings, if produced from a single pour 
into a single mold in a runner system) 
and, on a sampling basis, coupons cut 
from critical areas of production cast-
ings. The acceptance criteria for the 
process monitoring inspections and 
tests must be established and included 
in the process specifications to ensure 

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