Section 27.619

14 CFR Ch. I (1-1-19 Edition)

(1) Where applied loads are eventually distributed through a single member 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 elements would result in applied loads
being safely distributed to other loadcarrying members, 90 percent probability with 95 percent confidence.
(c) The strength, detail design, and
fabrication of the structure must minimize the probability of disastrous fatigue failure, particularly at points of
stress concentration.
(d) Design values may be those contained in the following publications
(available from the Naval Publications
and Forms Center, 5801 Tabor Avenue,
Philadelphia, Pennsylvania 19120) or
other values approved by the Administrator:
(1) MIL-HDBK-5,  - Metallic Materials
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 Construction 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 determined 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)))

spaschal on DSK3GDR082PROD with CFR

[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]

Section 27.619 Special factors.
(a) The special factors prescribed in
SectionSection 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 methods.
(b) For each part to which SectionSection 27.621
through 27.625 apply, the factor of safety prescribed in Section 27.303 must be multiplied by a special factor equal to - 
(1) The applicable special factors prescribed in SectionSection 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 uncertainties specified in paragraph (a) of
this section is extremely remote.
Section 27.621

Casting factors.

(a) General. The factors, tests, and inspections specified in paragraphs (b)
and (c) of this section must be applied
in addition to those necessary to establish foundry quality control. The inspections must meet approved specifications. Paragraphs (c) and (d) of this
section apply to structural castings except castings that are pressure tested
as parts of hydraulic 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 applicable 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 occupant, 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 particle (for ferromagnetic materials) or
penetrant (for nonferromagnetic materials) inspection methods or approved
equivalent inspection methods.
(2) For each critical casting with a
casting factor less than 1.50, three sample castings must be static tested and
shown to meet - 

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