477 

Federal Aviation Administration, DOT 

§ 25.979 

with the airplane in the ground atti-
tude. 

(c) Each fuel tank sump must have 

an accessible drain that— 

(1) Allows complete drainage of the 

sump on the ground; 

(2) Discharges clear of each part of 

the airplane; and 

(3) Has manual or automatic means 

for positive locking in the closed posi-
tion. 

§ 25.973

Fuel tank filler connection. 

Each fuel tank filler connection must 

prevent the entrance of fuel into any 
part of the airplane other than the 
tank itself. In addition— 

(a) [Reserved] 
(b) Each recessed filler connection 

that can retain any appreciable quan-
tity of fuel must have a drain that dis-
charges clear of each part of the air-
plane; 

(c) Each filler cap must provide a 

fuel-tight seal; and 

(d) Each fuel filling point must have 

a provision for electrically bonding the 
airplane to ground fueling equipment. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–40, 42 FR 15043, Mar. 17, 
1977; Amdt. 25–72, 55 FR 29785, July 20, 1990; 
Amdt. 25–115, 69 FR 40527, July 2, 2004] 

§ 25.975

Fuel tank vents and carbu-

retor vapor vents. 

(a) 

Fuel tank vents. Each fuel tank 

must be vented from the top part of the 
expansion space so that venting is ef-
fective under any normal flight condi-
tion. In addition— 

(1) Each vent must be arranged to 

avoid stoppage by dirt or ice forma-
tion; 

(2) The vent arrangement must pre-

vent siphoning of fuel during normal 
operation; 

(3) The venting capacity and vent 

pressure levels must maintain accept-
able differences of pressure between 
the interior and exterior of the tank, 
during— 

(i) Normal flight operation; 
(ii) Maximum rate of ascent and de-

scent; and 

(iii) Refueling and defueling (where 

applicable); 

(4) Airspaces of tanks with inter-

connected outlets must be inter-
connected; 

(5) There may be no point in any vent 

line where moisture can accumulate 
with the airplane in the ground atti-
tude or the level flight attitude, unless 
drainage is provided; and 

(6) No vent or drainage provision may 

end at any point— 

(i) Where the discharge of fuel from 

the vent outlet would constitute a fire 
hazard; or 

(ii) From which fumes could enter 

personnel compartments. 

(b) 

Carburetor vapor vents. Each car-

buretor with vapor elimination connec-
tions must have a vent line to lead va-
pors back to one of the fuel tanks. In 
addition— 

(1) Each vent system must have 

means to avoid stoppage by ice; and 

(2) If there is more than one fuel 

tank, and it is necessary to use the 
tanks in a definite sequence, each 
vapor vent return line must lead back 
to the fuel tank used for takeoff and 
landing. 

§ 25.977

Fuel tank outlet. 

(a) There must be a fuel strainer for 

the fuel tank outlet or for the booster 
pump. This strainer must— 

(1) For reciprocating engine powered 

airplanes, have 8 to 16 meshes per inch; 
and 

(2) For turbine engine powered air-

planes, prevent the passage of any ob-
ject that could restrict fuel flow or 
damage any fuel system component. 

(b) [Reserved] 
(c) The clear area of each fuel tank 

outlet strainer must be at least five 
times the area of the outlet line. 

(d) The diameter of each strainer 

must be at least that of the fuel tank 
outlet. 

(e) Each finger strainer must be ac-

cessible for inspection and cleaning. 

[Amdt. 25–11, 32 FR 6913, May 5, 1967, as 
amended by Amdt. 25–36, 39 FR 35460, Oct. 1, 
1974] 

§ 25.979

Pressure fueling system. 

For pressure fueling systems, the fol-

lowing apply: 

(a) Each pressure fueling system fuel 

manifold connection must have means 
to prevent the escape of hazardous 
quantities of fuel from the system if 
the fuel entry valve fails. 

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