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14 CFR Ch. I (1–1–14 Edition) 

§ 25.613 

§ 25.613

Material strength properties 

and material design values. 

(a) Material strength properties must 

be based on enough tests of material 
meeting approved specifications to es-
tablish design values on a statistical 
basis. 

(b) Material design values must be 

chosen to minimize the probability of 
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. The factors, tests, and in-

spections specified in paragraphs (b) 
through (d) of this section must be ap-
plied in addition to those necessary to 
establish foundry quality control. The 
inspections must meet approved speci-
fications. Paragraphs (c) and (d) of this 
section apply to any structural cast-
ings except castings that are pressure 
tested as parts of hydraulic or other 
fluid systems and do not support struc-
tural 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 airplane 
or result in serious injury to occu-
pants, 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 or penetrant inspection methods 
or approved equivalent nondestructive 
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— 

(i) The strength requirements of 

§ 25.305 at an ultimate load cor-
responding to a casting factor of 1.25; 
and 

(ii) The deformation requirements of 

§ 25.305 at a load of 1.15 times the limit 
load. 

(3) Examples of these castings are 

structural attachment fittings, parts of 

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