770 

14 CFR Ch. I (1–1–14 Edition) 

§ 29.861 

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. 

(g) 

Heater exhaust. Each heater ex-

haust system must meet the require-
ments of §§ 29.1121 and 29.1123. In addi-
tion— 

(1) Each exhaust shroud must be 

sealed so that no flammable fluids or 
hazardous quantities of vapors can 
reach the exhaust systems through 
joints; and 

(2) No exhaust system may restrict 

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

(h) 

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. 

(i) 

Drains.  There must be means for 

safe drainage of any fuel that might ac-
cumulate in 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 

against hazardous ice accumulation 
under any operating condition. 

[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as 
amended by Amdt. 29–2, 32 FR 6914, May 5, 
1967] 

§ 29.861

Fire protection of structure, 

controls, and other parts. 

Each part of the structure, controls, 

and the rotor mechanism, and other 
parts essential to controlled landing 
and (for category A) flight that would 
be affected by powerplant fires must be 
isolated under § 29.1191, or must be— 

(a) For category A rotorcraft, fire-

proof; and 

(b) For Category B rotorcraft, fire-

proof or protected so that they can per-
form their essential functions for at 

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