661
Federal Aviation Administration, DOT
§ 27.619
(1) Electrically bonding the compo-
nents properly to the airframe; or
(2) Designing the components so that
a strike will not endanger the rotor-
craft.
(c) For nonmetallic components,
compliance with paragraph (a) of this
section may be shown by—
(1) Designing the components to min-
imize the effect of a strike; or
(2) Incorporating acceptable means of
diverting the resulting electrical cur-
rent so as not to endanger the rotor-
craft.
(d) The electrical bonding and protec-
tion against lightning and static elec-
tricity must—
(1) Minimize the accumulation of
electrostatic charge;
(2) Minimize the risk of electric
shock to crew, passengers, and service
and maintenance personnel using nor-
mal precautions;
(3) Provide an electrical return path,
under both normal and fault condi-
tions, on rotorcraft having grounded
electrical systems; and
(4) Reduce to an acceptable level the
effects of static electricity on the func-
tioning of essential electrical and elec-
tronic equipment.
[Amdt. 27–21, 49 FR 44433, Nov. 6, 1984, as
amended by Amdt. 27–37, 64 FR 45094, Aug. 18,
1999; Amdt. 27–46, 76 FR 33135, June 8, 2011]
§ 27.611
Inspection provisions.
There must be means to allow the
close examination of each part that re-
quires—
(a) Recurring inspection;
(b) Adjustment for proper alignment
and functioning; or
(c) Lubrication.
§ 27.613
Material strength properties
and design values.
(a) Material strength properties must
be based on enough tests of material
meeting specifications to establish de-
sign values on a statistical basis.
(b) Design values must be chosen to
minimize the probability of structural
failure due to material variability. Ex-
cept as provided in paragraphs (d) and
(e) of this section, compliance with
this paragraph must be shown by se-
lecting design values that 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;
and
(2) For redundant structure, those in
which the failure of individual ele-
ments would result in applied loads
being safely distributed to other load-
carrying members, 90 percent prob-
ability with 95 percent confidence.
(c) The strength, detail design, and
fabrication of the structure must mini-
mize the probability of disastrous fa-
tigue failure, particularly at points of
stress concentration.
(d) Design values may be those con-
tained in the following publications
(available from the Naval Publications
and Forms Center, 5801 Tabor Avenue,
Philadelphia, Pennsylvania 19120) or
other values approved by the Adminis-
trator:
(1) MIL-HDBK-5, ‘‘Metallic Materials
and Elements for Flight Vehicle Struc-
ture’’.
(2) MIL-HDBK-17, ‘‘Plastics for
Flight Vehicles’’.
(3) ANC-18, ‘‘Design of Wood Aircraft
Structures’’.
(4) MIL-HDBK-23, ‘‘Composite Con-
struction 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 de-
termined 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. 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]
§ 27.619
Special factors.
(a) The special factors prescribed in
§§ 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—
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