693 

Federal Aviation Administration, DOT 

§ 31.41 

lack of rip stoppers. The selected fac-
tor must be applied to the more crit-
ical of the maximum operating pres-
sure or envelope stress. 

(c) A factor of safety of at least five 

must be used in the design of all fi-
brous or non-metallic parts of the rig-
ging and related attachments of the en-
velope to basket, trapeze, or other 
means provided for carrying occupants. 
The primary attachments of the enve-
lope to the basket, trapeze, or other 
means provided for carrying occupants 
must be designed so that failure is ex-
tremely 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 oper-
ating 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] 

§ 31.27

Strength. 

(a) The structure must be able to 

support limit loads without detri-
mental effect. 

(b) The structure must be substan-

tiated by test to be able to withstand 
the ultimate loads for at least three 
seconds without failure. For the enve-
lope, 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, strik-
ing 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 oc-
cupants. A drop test height of 36 
inches, or a drop test height that pro-
duces, upon impact, a velocity equal to 
the maximum vertical velocity deter-

mined in accordance with § 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 

§ 31.31

General. 

The suitability of each design detail 

or part that bears on safety must be es-
tablished by tests or analysis. 

§ 31.33

Materials. 

(a) The suitability and durability of 

all materials must be established on 
the basis of experience or tests. Mate-
rials must conform to approved speci-
fications 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. 

§ 31.35

Fabrication methods. 

The methods of fabrication used 

must produce a consistently sound 
structure. If a fabrication process re-
quires close control to reach this objec-
tive, the process must be performed in 
accordance with an approved process 
specification. 

§ 31.37

Fastenings. 

Only approved bolts, pins, screws, 

and rivets may be used in the struc-
ture. Approved locking devices or 
methods must be used for all these 
bolts, pins, and screws, unless the in-
stallation is shown to be free from vi-
bration. Self-locking nuts may not be 
used on bolts that are subject to rota-
tion in service. 

§ 31.39

Protection. 

Each part of the balloon must be 

suitably protected against deteriora-
tion or loss of strength in service due 
to weathering, corrosion, or other 
causes. 

§ 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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