(2) During ground test of the engine fire
detection system, an erroneous indication of system
fault may be encountered if an engine cowling is not
closed properly, or if the aircraft is headed toward a
strong external light source. In this circumstance,
close the cowling and/or change the aircraft heading to
enable a valid system check.
PROTECTION TEST, on the copilot's subpanel is
provided to test the engine fire detection system,
Figures 2-6 and 2-8. Before checkout, battery power
must be on and the FIRE DETR circuit breaker must
be closed. Switch position DETR 1 checks the area
forward of the air intake of each nacelle, including
circuits to the cockpit alarm and indication devices.
Switch position DETR 2 checks the circuits for the
upper accessory compartment of each nacelle. Switch
position DETR 3 checks the circuits for the lower
accessory compartment of each nacelle. Each
numbered switch position will initiate the cockpit
indications previously described.
2-31. ENGINE FIRE DETECTION SYSTEMS T2 .
a. A pneumatic fire detection system is installed
to provide an immediate warning in the event of a fire
or over temperature in the engine compartment. The
main element of the system is a temperature sensing
cable routed continuously throughout the engine
compartment, terminating in a responder unit. The
responder unit is mounted in the accessory area on
the upper left-hand engine truss just forward of the
engine firewall. The responder unit contains two sets
of contacts, a set of integrity switch contacts for
continuity test functions of the fire detection circuitry
and a set of alarm switch contacts that completes the
circuit to activate the fire warning system when the
detector cable senses an over temperature condition
in critical areas around the engine.
b. The sensor cable consists of an outer tube
filled with an inert gas and an inner hydride core that is
filled with an active gas. The gas within the tube forms
a pressure barrier that keeps the responder integrity
switch contacts closed for fire alarm continuity test
functions. As the temperature around the sensing
cable increases, the gases within the tube begin to
expand. When the pressure from the expanding
gases reaches a preset point, the contacts of the
responder alarm switch close, activating the respective
fire warning system.
c. The fire warning portion of the system
consists of two annunciators, placarded #1 FIRE
PULL and #2 FIRE PULL, located below the
glareshield, two MASTER WARNING annunciators
located on opposite sides of the glareshield, and two
responder units with pneumatic sensors in the engine
compartments. Refer to Figure 2-17.
d. An integrity switch that monitors the system is
held in the closed position. If the detector should
develop a leak, the loss of gas pressure would allow
the integrity switch to open and signal a lack of
detector integrity. The system then will not operate
during the system test function.
e. Testing the systems integrity, availability of
power, and the alarm annunciators (#1 and #2 FIRE
PULL and MASTER WARNING) is accomplished
through two switches located on the copilot's left
subpanel. The switches are placarded ENGINE FIRE
PROTECTION TEST LEFT DET / EXT and RIGHT
DET / EXT. When either the LEFT or the RIGHT
switch is placed in the DET position, electrical current
flows through a 5-ampere circuit breaker, placarded
FIRE DETR, located on the overhead circuit breaker
panel and the engine fire detector circuitry to the
integrity switch contacts in the respective responder
unit causing the respective alarm annunciators to
illuminate. If the circuit breaker opens, the system will
not operate during a test, or activate the annunciator
lights, if the detector cable should sense an
overtemperature condition. The system may be tested
either pre/post flight, or in flight as desired.
2-32. ENGINE FIRE EXTINGUISHER SYSTEM.
a. The fire extinguisher system utilizes an
explosive squib and valve which, when opened, allows
the distribution of the pressurized extinguishing agent
through a plumbing network of spray nozzles
strategically located in the fire zones of the engines.