Code of Federal Regulations - Title 14

615

Federal Aviation Administration, DOT

Pt. 25, App. N

communicate with a tank via a vent sys-
tem), and to any other confined spaces or en-
closed areas that could contain hazardous at-
mosphere under normal conditions or failure
conditions, must be permanently stenciled,
marked, or placarded to warn maintenance
personnel of the possible presence of a poten-
tially hazardous atmosphere.

M25.4

Airworthiness limitations and proce-

dures.

(a) If FRM is used to comply with para-

graph M25.1 of this appendix, Airworthiness
Limitations must be identified for all main-
tenance or inspection tasks required to iden-
tify failures of components within the FRM
that are needed to meet paragraph M25.1 of
this appendix.

(b) Maintenance procedures must be devel-

oped to identify any hazards to be considered
during maintenance of the FRM. These pro-
cedures must be included in the instructions
for continued airworthiness (ICA).

M25.5

Reliability reporting.

The effects of airplane component failures

on FRM reliability must be assessed on an
on-going basis. The applicant/holder must do
the following:

(a) Demonstrate effective means to ensure

collection of FRM reliability data. The
means must provide data affecting FRM reli-
ability, such as component failures.

(b) Unless alternative reporting procedures

are approved by the FAA Oversight Office, as
defined in part 26 of this subchapter, provide
a report to the FAA every six months for the
first five years after service introduction.
After that period, continued reporting every
six months may be replaced with other reli-
ability tracking methods found acceptable to
the FAA or eliminated if it is established
that the reliability of the FRM meets, and
will continue to meet, the exposure require-
ments of paragraph M25.1 of this appendix.

the applicable airplane manual, according to
a schedule approved by the FAA Oversight
Office, as defined in part 26 of this sub-
chapter, to correct any failures of the FRM
that occur in service that could increase any
fuel tank’s Fleet Average Flammability Ex-
posure to more than that required by para-
graph M25.1 of this appendix.

[Doc. No. FAA–2005–22997, 73 FR 42494, July
21, 2008]

PPENDIX

N TO P

ART

25—F

UEL

ANK

LAMMABILITY

XPOSURE AND

ELI

ABILITY

NALYSIS

N25.1

General.

(a) This appendix specifies the require-

ments for conducting fuel tank fleet average
flammability exposure analyses required to
meet § 25.981(b) and Appendix M of this part.
For fuel tanks installed in aluminum wings,
a qualitative assessment is sufficient if it

substantiates that the tank is a conven-
tional unheated wing tank.

(b) This appendix defines parameters af-

fecting fuel tank flammability that must be
used in performing the analysis. These in-
clude parameters that affect all airplanes
within the fleet, such as a statistical dis-
tribution of ambient temperature, fuel flash
point, flight lengths, and airplane descent
rate. Demonstration of compliance also re-
quires application of factors specific to the
airplane model being evaluated. Factors that
need to be included are maximum range,
cruise mach number, typical altitude where
the airplane begins initial cruise phase of
flight, fuel temperature during both ground
and flight times, and the performance of a
flammability reduction means (FRM) if in-
stalled.

ables, and data tables must be used in the
program to determine fleet average flamma-
bility exposure for a specific airplane model.

N25.2

Definitions.

(a)

Bulk Average Fuel Temperature means

the average fuel temperature within the fuel
tank or different sections of the tank if the
tank is subdivided by baffles or compart-
ments.

(b)

Flammability Exposure Evaluation Time

(FEET). The time from the start of preparing
the airplane for flight, through the flight
and landing, until all payload is unloaded,
and all passengers and crew have dis-
embarked. In the Monte Carlo program, the
flight time is randomly selected from the
Flight Length Distribution (Table 2), the
pre-flight times are provided as a function of
the flight time, and the post-flight time is a
constant 30 minutes.

(c)

Flammable. With respect to a fluid or

gas, flammable means susceptible to igniting
readily or to exploding (14 CFR Part 1, Defi-
nitions). A non-flammable ullage is one
where the fuel-air vapor is too lean or too
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 consid-
ered 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 flam-

mable fluid means the lowest temperature at
which the application of a flame to a heated
sample causes the vapor to ignite momen-
tarily, 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

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