spaschal on DSK3GDR082PROD with CFR

Federal Aviation Administration, DOT

Section 25.863

or reverse burning cannot enter the
ventilating airstream under any operating condition, including reverse flow
or malfunctioning of the heater or its
associated components; and
(2) No combustion air duct may restrict the prompt relief of any backfire
that, if so restricted, could cause heater failure.
(d) Heater controls; general. Provision
must be made to prevent the hazardous
accumulation of water or ice on or in
any heater control component, control
system tubing, or safety control.
(e) Heater safety controls. For each
combustion heater there must be the
following safety control means:
(1) Means independent of the components provided for the normal continuous control of air temperature, airflow, and fuel flow must be provided,
for each heater, to automatically shut
off the ignition and fuel supply to that
heater at a point remote from that
heater when any of the following occurs:
(i) The heat exchanger temperature
exceeds safe limits.
(ii) The ventilating air temperature
exceeds safe limits.
(iii) The combustion airflow becomes
inadequate for safe operation.
(iv) The ventilating airflow becomes
inadequate for safe operation.
(2) The means of complying with
paragraph (e)(1) of this section for any
individual heater must - 
(i) Be independent of components
serving any other heater whose heat
output is essential for safe operation;
and
(ii) Keep the heater off until restarted by the crew.
(3) There must be means to warn the
crew when any heater whose heat output is essential for safe operation has
been shut off by the automatic means
prescribed in paragraph (e)(1) of this
section.
(f) Air intakes. Each combustion and
ventilating air intake must be located
so that no flammable fluids or vapors
can enter the heater system under any
operating condition - 
(1) During normal operation; or
(2) As a result of the malfunctioning
of any other component.
(g) Heater exhaust. Heater exhaust
systems must meet the provisions of

SectionSection 25.1121 and 25.1123. In addition, there
must be provisions in the design of the
heater exhaust system to safely expel
the products of combustion to prevent
the occurrence of - 
(1) Fuel leakage from the exhaust to
surrounding compartments;
(2) Exhaust gas impingement on surrounding equipment or structure;
(3) Ignition of flammable fluids by
the exhaust, if the exhaust is in a compartment containing flammable fluid
lines; and
(4) Restriction by the exhaust of the
prompt relief of backfires that, if so restricted, could cause heater failure.
(h) Heater fuel systems. Each heater
fuel system must meet each powerplant fuel system requirement affecting safe heater operation. Each heater
fuel system component within the ventilating airstream must be protected
by shrouds so that no leakage from
those components can enter the ventilating airstream.
(i) Drains. There must be means to
safely drain fuel that might accumulate within the combustion chamber or
the heat exchanger. In addition - 
(1) Each part of any drain that operates at high temperatures must be protected in the same manner as heater
exhausts; and
(2) Each drain must be protected
from hazardous ice accumulation under
any operating condition.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-11, 32 FR 6912, May 5,
1967; Amdt. 25-23, 35 FR 5676, Apr. 8, 1970]

Section 25.863 Flammable fluid fire protection.
(a) In each area where flammable
fluids or vapors might escape by leakage of a fluid system, there must be
means to minimize the probability of
ignition of the fluids and vapors, and
the resultant hazards if ignition does
occur.
(b) Compliance with paragraph (a) of
this section must be shown by analysis
or tests, and the following factors must
be considered:
(1) Possible sources and paths of fluid
leakage, and means of detecting leakage.
(2) Flammability characteristics of
fluids, including effects of any combustible or absorbing materials.

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