(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 heater, if that region contains any
flammable fluid system components (including the heater fuel system), that
(i) Be damaged by heater malfunctioning; or
(ii) Allow flammable fluids or vapors to reach the heater in case of
(2) Each part of any ventilating air passage that --
(i) Surrounds the combustion chamber; and
(ii) Would not contain (without damage to other rotorcraft components)
any fire that may occur within the passage.
(b) Ventilating air ducts. Each ventilating air duct passing
through any fire zone must be fireproof. In addition --
(1) Unless isolation is provided by fireproof valves or by equally
effective means, the ventilating air duct downstream 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
system that the malfunctioning of any component of that system cannot
introduce flammable fluids or vapors into the ventilating airstream.
(c) Combustion air ducts. Each combustion air duct must be
fireproof for a distance great enough to prevent damage from backfiring or
reverse flame propagation. In addition --
(1) No combustion air duct may communicate with the ventilating
airstream unless flames from backfires or reverse burning cannot enter the
ventilating airstream under any operating condition, including reverse
flow or malfunction 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. There must be means 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, safety
control means must be provided as follows:
(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 of that heater at a point remote from that heater when any of the
(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 where 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 malfunction of any other component.
(g) Heater exhaust. Each heater exhaust system must meet the
requirements of §§29.1121 and 29.1123. In addition --
(1) Each exhaust shroud must be sealed so that no flammable fluids or
hazardous quantities of vapors can reach the exhaust systems through
(2) No exhaust system may restrict the prompt relief of any backfire
that, if so restricted, could cause heater failure.
(h) Heater fuel systems. Each heater fuel system must meet the
powerplant fuel system requirements affecting safe heater operation. Each
heater fuel system component in 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 for safe drainage of any fuel
that might accumulate in the combustion chamber or the heat exchanger. In
(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 against hazardous ice accumulation
under any operating condition.