781 

Federal Aviation Administration, DOT 

§ 29.955 

coupling has performed its intended 
function. 

(2) All individual breakaway cou-

plings, coupling fuel feed systems, or 
equivalent means must be designed, 
tested, installed, and maintained so in-
advertent fuel shutoff in flight is im-
probable in accordance with § 29.955(a) 
and must comply with the fatigue eval-
uation requirements of § 29.571 without 
leaking. 

(3) Alternate, equivalent means to 

the use of breakaway couplings must 
not create a survivable impact-induced 
load on the fuel line to which it is in-
stalled greater than 25 to 50 percent of 
the ultimate load (strength) of the 
weakest component in the line and 
must comply with the fatigue require-
ments of § 29.571 without leaking. 

(d) 

Frangible or deformable structural 

attachments.  Unless hazardous relative 
motion of fuel tanks and fuel system 
components to local rotorcraft struc-
ture is demonstrated to be extremely 
improbable in an otherwise survivable 
impact, frangible or locally deformable 
attachments of fuel tanks and fuel sys-
tem components to local rotorcraft 
structure must be used. The attach-
ment of fuel tanks and fuel system 
components to local rotorcraft struc-
ture, whether frangible or locally de-
formable, must be designed such that 
its separation or relative local defor-
mation will occur without rupture or 
local tear-out of the fuel tank or fuel 
system component that will cause fuel 
leakage. The ultimate strength of fran-
gible or deformable attachments must 
be as follows: 

(1) The load required to separate a 

frangible attachment from its support 
structure, or deform a locally deform-
able attachment relative to its support 
structure, must be between 25 and 50 
percent of the minimum ultimate load 
(ultimate strength) of the weakest 
component in the attached system. In 
no case may the load be less than 300 
pounds. 

(2) A frangible or locally deformable 

attachment must separate or locally 
deform as intended whenever its ulti-
mate load (as defined in paragraph 
(d)(1) of this section) is applied in the 
modes most likely to occur. 

(3) All frangible or locally deformable 

attachments must comply with the fa-
tigue requirements of § 29.571. 

(e) 

Separation of fuel and ignition 

sources.  To provide maximum crash re-
sistance, fuel must be located as far as 
practicable from all occupiable areas 
and from all potential ignition sources. 

(f) 

Other basic mechanical design cri-

teria.  Fuel tanks, fuel lines, electrical 
wires, and electrical devices must be 
designed, constructed, and installed, as 
far as practicable, to be crash resist-
ant. 

(g) 

Rigid or semirigid fuel tanks. Rigid 

or semirigid fuel tank or bladder walls 
must be impact and tear resistant. 

[Doc. No. 26352, 59 FR 50387, Oct. 3, 1994] 

§ 29.953

Fuel system independence. 

(a) For category A rotorcraft— 
(1) The fuel system must meet the re-

quirements of § 29.903(b); and 

(2) Unless other provisions are made 

to meet paragraph (a)(1) of this section, 
the fuel system must allow fuel to be 
supplied to each engine through a sys-
tem independent of those parts of each 
system supplying fuel to other engines. 

(b) Each fuel system for a multien-

gine category B rotorcraft must meet 
the requirements of paragraph (a)(2) of 
this section. However, separate fuel 
tanks need not be provided for each en-
gine. 

§ 29.954

Fuel system lightning protec-

tion. 

The fuel system must be designed 

and arranged to prevent the ignition of 
fuel vapor within the system by— 

(a) Direct lightning strikes to areas 

having a high probability of stroke at-
tachment; 

(b) Swept lightning strokes to areas 

where swept strokes are highly prob-
able; and 

(c) Corona and streamering at fuel 

vent outlets. 

[Amdt. 29–26, 53 FR 34217, Sept. 2, 1988] 

§ 29.955

Fuel flow. 

(a) 

General.  The fuel system for each 

engine must provide the engine with at 
least 100 percent of the fuel required 
under all operating and maneuvering 
conditions to be approved for the rotor-
craft, including, as applicable, the fuel 

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