478 

14 CFR Ch. I (1–1–14 Edition) 

§ 25.981 

(b) An automatic shutoff means must 

be provided to prevent the quantity of 
fuel in each tank from exceeding the 
maximum quantity approved for that 
tank. This means must— 

(1) Allow checking for proper shutoff 

operation before each fueling of the 
tank; and 

(2) Provide indication at each fueling 

station of failure of the shutoff means 
to stop the fuel flow at the maximum 
quantity approved for that tank. 

(c) A means must be provided to pre-

vent damage to the fuel system in the 
event of failure of the automatic shut-
off means prescribed in paragraph (b) 
of this section. 

(d) The airplane pressure fueling sys-

tem (not including fuel tanks and fuel 
tank vents) must withstand an ulti-
mate load that is 2.0 times the load 
arising from the maximum pressures, 
including surge, that is likely to occur 
during fueling. The maximum surge 
pressure must be established with any 
combination of tank valves being ei-
ther intentionally or inadvertently 
closed. 

(e) The airplane defueling system 

(not including fuel tanks and fuel tank 
vents) must withstand an ultimate 
load that is 2.0 times the load arising 
from the maximum permissible 
defueling pressure (positive or nega-
tive) at the airplane fueling connec-
tion. 

[Amdt. 25–11, 32 FR 6913, May 5, 1967, as 
amended by Amdt. 25–38, 41 FR 55467, Dec. 20, 
1976; Amdt. 25–72, 55 FR 29785, July 20, 1990] 

§ 25.981

Fuel tank ignition prevention. 

(a) No ignition source may be present 

at each point in the fuel tank or fuel 
tank system where catastrophic failure 
could occur due to ignition of fuel or 
vapors. This must be shown by: 

(1) Determining the highest tempera-

ture allowing a safe margin below the 
lowest expected autoignition tempera-
ture of the fuel in the fuel tanks. 

(2) Demonstrating that no tempera-

ture at each place inside each fuel tank 
where fuel ignition is possible will ex-
ceed the temperature determined under 
paragraph (a)(1) of this section. This 
must be verified under all probable op-
erating, failure, and malfunction con-
ditions of each component whose oper-

ation, failure, or malfunction could in-
crease the temperature inside the tank. 

(3) Demonstrating that an ignition 

source could not result from each sin-
gle failure, from each single failure in 
combination with each latent failure 
condition not shown to be extremely 
remote, and from all combinations of 
failures not shown to be extremely im-
probable. The effects of manufacturing 
variability, aging, wear, corrosion, and 
likely damage must be considered. 

(b) Except as provided in paragraphs 

(b)(2) and (c) of this section, no fuel 
tank Fleet Average Flammability Ex-
posure on an airplane may exceed three 
percent of the Flammability Exposure 
Evaluation Time (FEET) as defined in 
Appendix N of this part, or that of a 
fuel tank within the wing of the air-
plane model being evaluated, which-
ever is greater. If the wing is not a con-
ventional unheated aluminum wing, 
the analysis must be based on an as-
sumed Equivalent Conventional 
Unheated Aluminum Wing Tank. 

(1) Fleet Average Flammability Ex-

posure is determined in accordance 
with Appendix N of this part. The as-
sessment must be done in accordance 
with the methods and procedures set 
forth in the Fuel Tank Flammability 
Assessment Method User’s Manual, 
dated May 2008, document number 
DOT/FAA/AR–05/8 (incorporated by ref-
erence, see § 25.5). 

(2) Any fuel tank other than a main 

fuel tank on an airplane must meet the 
flammability exposure criteria of Ap-
pendix M to this part if any portion of 
the tank is located within the fuselage 
contour. 

(3) As used in this paragraph, 
(i) 

Equivalent Conventional Unheated 

Aluminum Wing Tank is an integral 
tank in an unheated semi-monocoque 
aluminum wing of a subsonic airplane 
that is equivalent in aerodynamic per-
formance, structural capability, fuel 
tank capacity and tank configuration 
to the designed wing. 

(ii) 

Fleet Average Flammability Expo-

sure  is defined in Appendix N to this 
part and means the percentage of time 
each fuel tank ullage is flammable for 
a fleet of an airplane type operating 
over the range of flight lengths. 

(iii) 

Main Fuel Tank means a fuel 

tank that feeds fuel directly into one 

VerDate Mar<15>2010 

10:12 Mar 18, 2014

Jkt 232046

PO 00000

Frm 00488

Fmt 8010

Sfmt 8010

Y:\SGML\232046.XXX

232046

pmangrum on DSK3VPTVN1PROD with CFR