Section 29.611

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

and maintenance personnel using normal precautions;
(3) Provide and electrical return
path, under both normal and fault conditions, on rotorcraft having grounded
electrical systems; and
(4) Reduce to an acceptable level the
effects of static electricity on the functioning of essential electrical and electronic equipment.
[Amdt. 29-24, 49 FR 44437, Nov. 6, 1984; Amdt.
29-40, 61 FR 21907, May 10, 1996; 61 FR 33963,
July 1, 1996; Amdt. 29-53, 76 FR 33135, June 8,
2011]

spaschal on DSK3GDR082PROD with CFR

Section 29.611 Inspection provisions.
There must be means to allow close
examination of each part that requires - 
(a) Recurring inspection;
(b) Adjustment for proper alignment
and functioning; or
(c) Lubrication.
Section 29.613 Material strength properties
and design values.
(a) Material strength properties must
be based on enough tests of material
meeting specifications to establish design values on a statistical basis.
(b) Design values must be chosen to
minimize the probability of structural
failure due to material variability. Except as provided in paragraphs (d) and
(e) of this section, compliance with
this paragraph must be shown by selecting design values that assure material strength with the following probability - 
(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 structures, 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, PA 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)))
[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as
amended by Amdt. 29-17, 43 FR 50599, Oct. 30,
1978; Amdt. 29-30, 55 FR 8003, Mar. 6, 1990]

Section 29.619 Special factors.
(a) The special factors prescribed in
SectionSection 29.621 through 29.625 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 of the rotorcraft to
which SectionSection 29.621 through 29.625 apply, the
factor of safety prescribed in Section 29.303
must be multiplied by a special factor
equal to - 
(1) The applicable special factors prescribed in SectionSection 29.621 through 29.625; 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 29.621 Casting factors.
(a) General. The factors, tests, and inspections specified in paragraphs (b)
and (c) of this section must be applied

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