Federal Aviation Administration, DOT

Section 31.41

lack of rip stoppers. The selected factor must be applied to the more critical of the maximum operating pressure or envelope stress.
(c) A factor of safety of at least five
must be used in the design of all fibrous or non-metallic parts of the rigging and related attachments of the envelope to basket, trapeze, or other
means provided for carrying occupants.
The primary attachments of the envelope to the basket, trapeze, or other
means provided for carrying occupants
must be designed so that failure is extremely remote or so that any single
failure will not jeopardize safety of
flight.
(d) In applying factors of safety, the
effect of temperature, and other operating characteristics, or both, that
may affect strength of the balloon
must be accounted for.
(e) For design purposes, an occupant
weight of at least 170 pounds must be
assumed.
[Doc. No. 1437, 29 FR 8258, July 1, 1964, as
amended by Amdt. 31-2, 30 FR 3377, Mar. 13,
1965]

spaschal on DSK3GDR082PROD with CFR

Section 31.27

Strength.

(a) The structure must be able to
support limit loads without detrimental effect.
(b) The structure must be substantiated by test to be able to withstand
the ultimate loads for at least three
seconds without failure. For the envelope, a test of a representative part is
acceptable, if the part tested is large
enough to include critical seams,
joints, and load attachment points and
members.
(c) An ultimate free-fall drop test
must be made of the basket, trapeze, or
other place provided for occupants. The
test must be made at design maximum
weight on a horizontal surface, with
the basket, trapeze, or other means
provided for carrying occupants, striking the surface at angles of 0, 15, and 30
degrees. The weight may be distributed
to simulate actual conditions. There
must be no distortion or failure that is
likely to cause serious injury to the occupants. A drop test height of 36
inches, or a drop test height that produces, upon impact, a velocity equal to
the maximum vertical velocity deter-

mined in accordance with Section 31.19,
whichever is higher, must be used.
[Doc. No. 1437, 29 FR 8258, July 1, 1964, as
amended by Amdt. 31-4, 45 FR 60179, Sept. 11,
1980]

Subpart D - Design Construction
Section 31.31 General.
The suitability of each design detail
or part that bears on safety must be established by tests or analysis.
Section 31.33 Materials.
(a) The suitability and durability of
all materials must be established on
the basis of experience or tests. Materials must conform to approved specifications that will ensure that they
have the strength and other properties
assumed in the design data.
(b) Material strength properties must
be based on enough tests of material
conforming to specifications so as to
establish design values on a statistical
basis.
Section 31.35 Fabrication methods.
The methods of fabrication used
must produce a consistently sound
structure. If a fabrication process requires close control to reach this objective, the process must be performed in
accordance with an approved process
specification.
Section 31.37 Fastenings.
Only approved bolts, pins, screws,
and rivets may be used in the structure. Approved locking devices or
methods must be used for all these
bolts, pins, and screws, unless the installation is shown to be free from vibration. Self-locking nuts may not be
used on bolts that are subject to rotation in service.
Section 31.39 Protection.
Each part of the balloon must be
suitably protected against deterioration or loss of strength in service due
to weathering, corrosion, or other
causes.
Section 31.41 Inspection provisions.
There must be a means to allow close
examination of each part that require
repeated inspection and adjustment.

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