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14 CFR Ch. I (1–1–19 Edition)
§ 25.609
§ 25.609
Protection of structure.
Each part of the structure must—
(a) Be suitably protected against de-
terioration or loss of strength in serv-
ice due to any cause, including—
(1) Weathering;
(2) Corrosion; and
(3) Abrasion; and
(b) Have provisions for ventilation
and drainage where necessary for pro-
tection.
§ 25.611
Accessibility provisions.
(a)Means must be provided to allow
inspection (including inspection of
principal structural elements and con-
trol systems), replacement of parts
normally requiring replacement, ad-
justment, and lubrication as necessary
for continued airworthiness. The in-
spection means for each item must be
practicable for the inspection interval
for the item. Nondestructive inspection
aids may be used to inspect structural
elements where it is impracticable to
provide means for direct visual inspec-
tion if it is shown that the inspection
is effective and the inspection proce-
dures are specified in the maintenance
manual required by § 25.1529.
(b) EWIS must meet the accessibility
requirements of § 25.1719.
[Amdt. 25–23, 35 FR 5674, Apr. 8, 1970, as
amended by Amdt. 25–123, 72 FR 63404, Nov. 8,
2007]
§ 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.
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
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