307 

Federal Aviation Administration, DOT 

§ 25.863 

or reverse burning cannot enter the 
ventilating airstream under any oper-
ating condition, including reverse flow 
or malfunctioning of the heater or its 
associated components; and 

(2) No combustion air duct may re-

strict the prompt relief of any backfire 
that, if so restricted, could cause heat-
er 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 compo-

nents provided for the normal contin-
uous control of air temperature, air-
flow, 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 oc-
curs: 

(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 re-

started by the crew. 

(3) There must be means to warn the 

crew when any heater whose heat out-
put 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 

§§ 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 sur-

rounding equipment or structure; 

(3) Ignition of flammable fluids by 

the exhaust, if the exhaust is in a com-
partment containing flammable fluid 
lines; and 

(4) Restriction by the exhaust of the 

prompt relief of backfires that, if so re-
stricted, could cause heater failure. 

(h) 

Heater fuel systems. 

Each heater 

fuel system must meet each power-
plant fuel system requirement affect-
ing safe heater operation. Each heater 
fuel system component within the ven-
tilating airstream must be protected 
by shrouds so that no leakage from 
those components can enter the ven-
tilating airstream. 

(i) 

Drains. 

There must be means to 

safely drain fuel that might accumu-
late within the combustion chamber or 
the heat exchanger. In addition— 

(1) Each part of any drain that oper-

ates at high temperatures must be pro-
tected 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] 

§ 25.863

Flammable fluid fire protec-

tion. 

(a) In each area where flammable 

fluids or vapors might escape by leak-
age 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 leak-
age. 

(2) Flammability characteristics of 

fluids, including effects of any combus-
tible or absorbing materials. 

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