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694 

14 CFR Ch. I (1–1–24 Edition) 

§ 31.43 

§ 31.43

Fitting factor. 

(a) A fitting factor of at least 1.15 

must be used in the analysis of each 
fitting the strength of which is not 
proven by limit and ultimate load tests 
in which the actual stress conditions 
are simulated in the fitting and sur-
rounding structure. This factor applies 
to all parts of the fitting, the means of 
attachment, and the bearing on the 
members joined. 

(b) Each part with an integral fitting 

must be treated as a fitting up to the 
point where the section properties be-
come typical of the member. 

(c) The fitting factor need not be 

used if the joint design is made in ac-
cordance with approved practices and 
is based on comprehensive test data. 

§ 31.45

Fuel cells. 

If fuel cells are used, the fuel cells, 

their attachments, and related sup-
porting structure must be shown by 
tests to be capable of withstanding, 
without detrimental distortion or fail-
ure, any inertia loads to which the in-
stallation may be subjected, including 
the drop tests prescribed in § 31.27(c). In 
the tests, the fuel cells must be loaded 
to the weight and pressure equivalent 
to the full fuel quantity condition. 

[Amdt. 31–3, 41 FR 55474, Dec. 20, 1976] 

§ 31.46

Pressurized fuel systems. 

For pressurized fuel systems, each 

element and its connecting fittings and 
lines must be tested to an ultimate 
pressure of at least twice the maximum 
pressure to which the system will be 
subjected in normal operation. No part 
of the system may fail or malfunction 
during the test. The test configuration 
must be representative of the normal 
fuel system installation and balloon 
configuration. 

[Amdt. 31–3, 41 FR 55474, Dec. 20, 1976] 

§ 31.47

Burners. 

(a) If a burner is used to provide the 

lifting means, the system must be de-
signed and installed so as not to create 
a fire hazard. 

(b) There must be shielding to pro-

tect parts adjacent to the burner 
flame, and the occupants, from heat ef-
fects. 

(c) There must be controls, instru-

ments, or other equipment essential to 
the safe control and operation of the 
heater. They must be shown to be able 
to perform their intended functions 
during normal and emergency oper-
ation. 

(d) The burner system (including the 

burner unit, controls, fuel lines, fuel 
cells, regulators, control valves, and 
other related elements) must be sub-
stantiated by an endurance test of at 
least 40 hours. Each element of the sys-
tem must be installed and tested to 
simulate actual balloon installation 
and use. 

(1) The test program for the main 

blast valve operation of the burner 
must include: 

(i) Five hours at the maximum fuel 

pressure for which approval is sought, 
with a burn time for each one minute 
cycle of three to ten seconds. The burn 
time must be established so that each 
burner is subjected to the maximum 
thermal shock for temperature affected 
elements; 

(ii) Seven and one-half hours at an 

intermediate fuel pressure, with a burn 
time for each one minute cycle of three 
to ten seconds. An intermediate fuel 
pressure is 40 to 60 percent of the range 
between the maximum fuel pressure 
referenced in paragraph (d)(1)(i) of this 
section and minimum fuel pressure ref-
erenced in paragraph (d)(1)(iii); 

(iii) Six hours and fifteen minutes at 

the minimum fuel pressure for which 
approval is sought, with a burn time 
for each one minute cycle of three to 
ten seconds; 

(iv) Fifteen minutes of operation on 

vapor, with a burn time for each one 
minute cycle of at least 30 seconds; and 

(v) Fifteen hours of normal flight op-

eration. 

(2) The test program for the sec-

ondary or backup operation of the 
burner must include six hours of oper-
ation with a burn time for each five 
minute cycle of one minute at an inter-
mediate fuel pressure. 

(e) The test must also include at 

least three flameouts and restarts. 

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695 

Federal Aviation Administration, DOT 

§ 31.61 

(f) Each element of the system must 

be serviceable at the end of the test. 

[Doc. No. 1437, 29 FR 8258, July 1, 1964, as 
amended by Amdt. 31–2, 30 FR 3377, Mar. 13, 
1965; Amdt. 31–7, 61 FR 18223, Apr. 24, 1996; 61 
FR 20877, May 8, 1996] 

§ 31.49

Control systems. 

(a) Each control must operate easily, 

smoothly, and positively enough to 
allow proper performance of its func-
tions. Controls must be arranged and 
identified to provide for convenience of 
operation and to prevent the possi-
bility of confusion and subsequent in-
advertent operation. 

(b) Each control system and oper-

ating device must be designed and in-
stalled in a manner that will prevent 
jamming, chafing, or interference from 
passengers, cargo, or loose objects. Pre-
caution must be taken to prevent for-
eign objects from jamming the con-
trols. The elements of the control sys-
tem must have design features or must 
be distinctly and permanently marked 
to minimize the possibility of incorrect 
assembly that could result in malfunc-
tioning of the control system. 

(c) Each balloon using a captive gas 

as the lifting means must have an 
automatic valve or appendix that is 
able to release gas automatically at 
the rate of at least three percent of the 
total volume per minute when the bal-
loon is at its maximum operating pres-
sure. 

(d) Each hot air balloon must have a 

means to allow the controlled release 
of hot air during flight. 

(e) Each hot air balloon must have a 

means to indicate the maximum enve-
lope skin temperatures occurring dur-
ing operation. The indicator must be 
readily visible to the pilot and marked 
to indicate the limiting safe tempera-
ture of the envelope material. If the 
markings are on the cover glass of the 
instrument, there must be provisions 
to maintain the correct alignment of 
the glass cover with the face of the 
dial. 

[Doc. No. 1437, 29 FR 8258, July 1, 1964, as 
amended by Amdt. 31–2, 30 FR 3377, Mar. 13, 
1965] 

§ 31.51

Ballast. 

Each captive gas balloon must have a 

means for the safe storage and con-

trolled release of ballast. The ballast 
must consist of material that, if re-
leased during flight, is not hazardous 
to persons on the ground. 

§ 31.53

Drag rope. 

If a drag rope is used, the end that is 

released overboard must be stiffened to 
preclude the probability of the rope be-
coming entangled with trees, wires, or 
other objects on the ground. 

§ 31.55

Deflation means. 

There must be a means to allow 

emergency deflation of the envelope so 
as to allow a safe emergency landing. If 
a system other than a manual system 
is used, the reliability of the system 
used must be substantiated. 

[Amdt. 31–2, 30 FR 3377, Mar. 13, 1965] 

§ 31.57

Rip cords. 

(a) If a rip cord is used for emergency 

deflation, it must be designed and in-
stalled to preclude entanglement. 

(b) The force required to operate the 

rip cord may not be less than 25, or 
more than 75, pounds. 

(c) The end of the rip cord to be oper-

ated by the pilot must be colored red. 

(d) The rip cord must be long enough 

to allow an increase of at least 10 per-
cent in the vertical dimension of the 
envelope. 

§ 31.59

Trapeze, basket, or other 

means provided for occupants. 

(a) The trapeze, basket, or other 

means provided for carrying occupants 
may not rotate independently of the 
envelope. 

(b) Each projecting object on the tra-

peze, basket, or other means provided 
for carrying occupants, that could 
cause injury to the occupants, must be 
padded. 

§ 31.61

Static discharge. 

Unless shown not to be necessary for 

safety, there must be appropriate bond-
ing means in the design of each balloon 
using flammable gas as a lifting means 
to ensure that the effects of static dis-
charges will not create a hazard. 

[Amdt. 31–2, 30 FR 3377, Mar. 13, 1965] 

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