Appendix M to Part 25 - Fuel Tank System Flammability Reduction Means
14:1.0.1.3.12.12.121.1.18 : Appendix M
Appendix M to Part 25 - Fuel Tank System Flammability Reduction
Means
M25.1 Fuel tank flammability exposure requirements.
(a) The Fleet Average Flammability Exposure of each fuel tank,
as determined in accordance with Appendix N of this part, may not
exceed 3 percent of the Flammability Exposure Evaluation Time
(FEET), as defined in Appendix N of this part. As a portion of this
3 percent, if flammability reduction means (FRM) are used, each of
the following time periods may not exceed 1.8 percent of the
FEET:
(1) When any FRM is operational but the fuel tank is not inert
and the tank is flammable; and
(2) When any FRM is inoperative and the tank is flammable.
(b) The Fleet Average Flammability Exposure, as defined in
Appendix N of this part, of each fuel tank may not exceed 3 percent
of the portion of the FEET occurring during either ground or
takeoff/climb phases of flight during warm days. The analysis must
consider the following conditions.
(1) The analysis must use the subset of those flights that begin
with a sea level ground ambient temperature of 80 °F (standard day
plus 21 °F atmosphere) or above, from the flammability exposure
analysis done for overall performance.
(2) For the ground and takeoff/climb phases of flight, the
average flammability exposure must be calculated by dividing the
time during the specific flight phase the fuel tank is flammable by
the total time of the specific flight phase.
(3) Compliance with this paragraph may be shown using only those
flights for which the airplane is dispatched with the flammability
reduction means operational.
M25.2 Showing compliance.
(a) The applicant must provide data from analysis, ground
testing, and flight testing, or any combination of these, that:
(1) Validate the parameters used in the analysis required by
paragraph M25.1 of this appendix;
(2) Substantiate that the FRM is effective at limiting
flammability exposure in all compartments of each tank for which
the FRM is used to show compliance with paragraph M25.1 of this
appendix; and
(3) Describe the circumstances under which the FRM would not be
operated during each phase of flight.
(b) The applicant must validate that the FRM meets the
requirements of paragraph M25.1 of this appendix with any airplane
or engine configuration affecting the performance of the FRM for
which approval is sought.
M25.3 Reliability indications and maintenance access.
(a) Reliability indications must be provided to identify
failures of the FRM that would otherwise be latent and whose
identification is necessary to ensure the fuel tank with an FRM
meets the fleet average flammability exposure requirements listed
in paragraph M25.1 of this appendix, including when the FRM is
inoperative.
(b) Sufficient accessibility to FRM reliability indications must
be provided for maintenance personnel or the flightcrew.
(c) The access doors and panels to the fuel tanks with FRMs
(including any tanks that communicate with a tank via a vent
system), and to any other confined spaces or enclosed areas that
could contain hazardous atmosphere under normal conditions or
failure conditions, must be permanently stenciled, marked, or
placarded to warn maintenance personnel of the possible presence of
a potentially hazardous atmosphere.
M25.4 Airworthiness limitations and procedures.
(a) If FRM is used to comply with paragraph M25.1 of this
appendix, Airworthiness Limitations must be identified for all
maintenance or inspection tasks required to identify failures of
components within the FRM that are needed to meet paragraph M25.1
of this appendix.
(b) Maintenance procedures must be developed to identify any
hazards to be considered during maintenance of the FRM. These
procedures 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
reliability, such as component failures.
(b) Unless alternative reporting procedures are approved by the
responsible Aircraft Certification Service 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 reliability 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 requirements of
paragraph M25.1 of this appendix.
(c) Develop service instructions or revise the applicable
airplane manual, according to a schedule approved by the
responsible Aircraft Certification Service office, as defined in
part 26 of this subchapter, to correct any failures of the FRM that
occur in service that could increase any fuel tank's Fleet Average
Flammability Exposure to more than that required by paragraph M25.1
of this appendix.
[Doc. No. FAA-2005-22997, 73 FR 42494, July 21, 2008, as amended by
Doc. No. FAA-2018-0119, Amdt. 25-145, 83 FR 9169, Mar. 5, 2018]