621 

Federal Aviation Administration, DOT 

§ 29.859 

(3) Sources of heat within each com-

partment must be shielded and insu-
lated to prevent igniting the cargo. 

[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as 
amended by Amdt. 29–3, 33 FR 969, Jan. 26, 
1968; Amdt. 29–24, 49 FR 44438, Nov. 6, 1984; 
Amdt. 27–26, 55 FR 8004, Mar. 6, 1990] 

§ 29.859

Combustion heater fire pro-

tection. 

(a) 

Combustion heater fire zones. 

The 

following combustion heater fire zones 
must be protected against fire under 
the applicable provisions of §§ 29.1181 
through 29.1191, and 29.1195 through 
29.1203: 

(1) The region surrounding any heat-

er, if that region contains any flam-
mable fluid system components (in-
cluding the heater fuel system), that 
could— 

(i) Be damaged by heater malfunc-

tioning; or 

(ii) Allow flammable fluids or vapors 

to reach the heater in case of leakage. 

(2) Each part of any ventilating air 

passage that— 

(i) Surrounds the combustion cham-

ber; and 

(ii) Would not contain (without dam-

age to other rotorcraft components) 
any fire that may occur within the pas-
sage. 

(b) 

Ventilating air ducts. 

Each ven-

tilating air duct passing through any 
fire zone must be fireproof. In addi-
tion— 

(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; and 

(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. 

(c) 

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. In addition— 

(1) No combustion air duct may com-

municate with the ventilating air-

stream unless flames from backfires or 
reverse burning cannot enter the ven-
tilating airstream under any operating 
condition, including reverse flow or 
malfunction of the heater or its associ-
ated 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. 

There 

must be means to prevent the haz-
ardous accumulation of water or ice on 
or in any heater control component, 
control system tubing, or safety con-
trol. 

(e) 

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 (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 where 
no flammable fluids or vapors can 
enter the heater system under any op-
erating condition— 

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

any other component. 

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