spaschal on DSK3GDR082PROD with CFR

Pt. 25, App. N

14 CFR Ch. I (1-1-19 Edition)

rich to burn or is inert as defined below. For
the purposes of this appendix, a fuel tank
that is not inert is considered flammable
when the bulk average fuel temperature
within the tank is within the flammable
range for the fuel type being used. For any
fuel tank that is subdivided into sections by
baffles or compartments, the tank is considered flammable when the bulk average fuel
temperature within any section of the tank,
that is not inert, is within the flammable
range for the fuel type being used.
(d) Flash Point. The flash point of a flammable fluid means the lowest temperature at
which the application of a flame to a heated
sample causes the vapor to ignite momentarily, or  - flash. -  Table 1 of this appendix
provides the flash point for the standard fuel
to be used in the analysis.
(e) Fleet average flammability exposure is the
percentage of the flammability exposure
evaluation time (FEET) each fuel tank
ullage is flammable for a fleet of an airplane
type operating over the range of flight
lengths in a world-wide range of environmental conditions and fuel properties as defined in this appendix.
(f) Gaussian Distribution is another name
for the normal distribution, a symmetrical
frequency distribution having a precise
mathematical formula relating the mean
and standard deviation of the samples.
Gaussian distributions yield bell-shaped frequency curves having a preponderance of values around the mean with progressively
fewer observations as the curve extends outward.
(g) Hazardous atmosphere. An atmosphere
that may expose maintenance personnel,
passengers or flight crew to the risk of
death, incapacitation, impairment of ability
to self-rescue (that is, escape unaided from a
confined space), injury, or acute illness.
(h) Inert. For the purpose of this appendix,
the tank is considered inert when the bulk
average oxygen concentration within each
compartment of the tank is 12 percent or less
from sea level up to 10,000 feet altitude, then
linearly increasing from 12 percent at 10,000
feet to 14.5 percent at 40,000 feet altitude,
and extrapolated linearly above that altitude.
(i) Inerting. A process where a noncombustible gas is introduced into the ullage of a
fuel tank so that the ullage becomes nonflammable.
(j) Monte Carlo Analysis. The analytical
method that is specified in this appendix as
the compliance means for assessing the fleet
average flammability exposure time for a
fuel tank.
(k) Oxygen evolution occurs when oxygen
dissolved in the fuel is released into the
ullage as the pressure and temperature in
the fuel tank are reduced.
(l) Standard deviation is a statistical measure of the dispersion or variation in a dis-

tribution, equal to the square root of the
arithmetic mean of the squares of the deviations from the arithmetic means.
(m) Transport Effects. For purposes of this
appendix, transport effects are the change in
fuel vapor concentration in a fuel tank
caused by low fuel conditions and fuel condensation and vaporization.
(n) Ullage. The volume within the fuel tank
not occupied by liquid fuel.
N25.3 Fuel tank flammability exposure analysis.
(a) A flammability exposure analysis must
be conducted for the fuel tank under evaluation to determine fleet average flammability
exposure for the airplane and fuel types
under evaluation. For fuel tanks that are
subdivided by baffles or compartments, an
analysis must be performed either for each
section of the tank, or for the section of the
tank having the highest flammability exposure. Consideration of transport effects is
not allowed in the analysis. The analysis
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
reference, see Section 25.5). The parameters specified in sections N25.3(b) and (c) of this appendix must be used in the fuel tank flammability exposure  - Monte Carlo -  analysis.
(b) The following parameters are defined in
the Monte Carlo analysis and provided in
paragraph N25.4 of this appendix:
(1) Cruise Ambient Temperature, as defined in this appendix.
(2) Ground Ambient Temperature, as defined in this appendix.
(3) Fuel Flash Point, as defined in this appendix.
(4) Flight Length Distribution, as defined
in Table 2 of this appendix.
(5) Airplane Climb and Descent Profiles, as
defined in the Fuel Tank Flammability Assessment Method User-s Manual, dated May
2008, document number DOT/FAA/AR-05/8
(incorporated by reference in Section 25.5).
(c) Parameters that are specific to the particular airplane model under evaluation that
must be provided as inputs to the Monte
Carlo analysis are:
(1) Airplane cruise altitude.
(2) Fuel tank quantities. If fuel quantity
affects fuel tank flammability, inputs to the
Monte Carlo analysis must be provided that
represent the actual fuel quantity within the
fuel tank or compartment of the fuel tank
throughout each of the flights being evaluated. Input values for this data must be obtained from ground and flight test data or
the approved FAA fuel management procedures.
(3) Airplane cruise mach number.
(4) Airplane maximum range.

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