a control unit which monitors the electrical re-
sistance of the sensing elements. The sensing
elements are made of Inconel metal tubing
filled with a pliable, heat-sensitive ceramic ma-
terial which, in turn, encloses a conductor
wire at its center. The electrical resistance of
the ceramic material is relatively high at nor-
mal temperatures. At high temperatures, how-
ever, the electrical resistance decreases and
allows increased current flow.
The control unit detects the increased current
flow and energizes the red FIRE warning light
on the glareshield (or on the readout panel on
airplanes without glareshield warning lights)
when temperature reaches 510ºF in the rear
nacelle area, or 480ºF in the forward nacelle
area. A system test switch is installed forward
of the throttle quadrant to check the continu-
ity of the sensing elements and control units.
The control units are located in the tailcone ex-
cept for airplanes 23-003 through 24-129. On
these airplanes, they are located in the nose
compartment.
DC electrical power for the system is supplied
through circuit breakers on the appropriate
pilot’s and/or copilot’s circuit-breaker panels.
FIRE LIGHTS
The red FIRE warning lights are located at
each end of the glareshield (Figure 8-1) or on
the readout panel of airplanes without
glareshield warning lights. In the event of an
engine fire, the applicable light flashes until
the overheat condition ceases to exist. On air-
planes without glareshield lights, the FIRE
light does not flash.
FIRE DETECTION SYSTEM TEST
The FIRE DET test switch on the forward end
of the throttle quadrant (Figure 8-2) is used to
test continuity of the sensing elements and
control units. On airplanes with glareshield
lights, positioning the switch to TEST causes
the FIRE lights to flash. On airplanes without
glareshield lights, the FIRE lights remain on
8-2
FOR TRAINING PURPOSES ONLY
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