524 

14 CFR Ch. I (1–1–19 Edition) 

§ 27.859 

(d) 

Ventilating air ducts. 

Each ven-

tilating air duct passing through any 
heater region must be fireproof. 

(1) Unless isolation is provided by 

fireproof valves or by equally effective 
means, the ventilating air duct down-
stream of each heater must be fireproof 
for a distance great enough to ensure 
that any fire originating in the heater 
can be contained in the duct. 

(2) Each part of any ventilating duct 

passing through any region having a 
flammable fluid system must be so 
constructed or isolated from that sys-
tem that the malfunctioning of any 
component of that system cannot in-
troduce flammable fluids or vapors 
into the ventilating airstream. 

(e) 

Combustion air ducts. 

Each com-

bustion air duct must be fireproof for a 
distance great enough to prevent dam-
age from backfiring or reverse flame 
propagation. 

(1) No combustion air duct may con-

nect with the ventilating airstream un-
less flames from backfires or reverse 
burning cannot enter the ventilating 
airstream under any operating condi-
tion, including reverse flow or mal-
function of the heater or its associated 
components. 

(2) No combustion air duct may re-

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

(f) 

Heater control: General. 

There must 

be means to prevent the hazardous ac-
cumulation of water or ice on or in any 
heater control component, control sys-
tem tubing, or safety control. 

(g) 

Heater safety controls. 

For each 

combustion heater, safety control 
means must be provided as follows: 

(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 of 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 (g)(1) of this section for any 
individual heater must— 

(i) Be independent of components 

serving any other heater, the heat out-
put of which is essential for safe oper-
ation; and 

(ii) Keep the heater off until re-

started by the crew. 

(3) There must be means to warn the 

crew when any heater, the heat output 
of which is essential for safe operation, 
has been shut off by the automatic 
means prescribed in paragraph (g)(1) of 
this section. 

(h) 

Air intakes. 

Each combustion and 

ventilating air intake must be located 
so that no flammable fluids or vapors 
can enter the heater system— 

(1) During normal operation; or 
(2) As a result of the malfunction of 

any other component. 

(i) 

Heater exhaust. 

Each heater ex-

haust system must meet the require-
ments of §§ 27.1121 and 27.1123. 

(1) Each exhaust shroud must be 

sealed so that no flammable fluids or 
hazardous quantities of vapors can 
reach the exhaust system through 
joints. 

(2) No exhaust system may restrict 

the prompt relief of any backfire that, 
if so restricted, could cause heater fail-
ure. 

(j) 

Heater fuel systems. 

Each heater 

fuel system must meet the powerplant 
fuel system requirements affecting safe 
heater operation. Each heater fuel sys-
tem component in the ventilating air-
stream must be protected by shrouds 
so that no leakage from those compo-
nents can enter the ventilating air-
stream. 

(k) 

Drains. 

There must be means for 

safe drainage of any fuel that might ac-
cumulate in the combustion chamber 
or the heat exchanger. 

(1) Each part of any drain that oper-

ates at high temperatures must be pro-
tected in the same manner as heater 
exhausts. 

(2) Each drain must be protected 

against hazardous ice accumulation 
under any operating condition. 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–23, 53 FR 34211, Sept. 2, 
1988] 

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