General; Fire Detection; Components - BOMBARDIER Challenger 601-3A CL-600-2B16 Pilot Training Manual

GENERAL

Fire and overheat detection is provided for
each powerplant and for the APU. The pow-
erplant fire zones are the area outside the core
cowls (including the powerplant accessory
gearbox section and the nacelle/pylon) and
the area inside the core cowls. The APU fire
zone is the area within the APU enclosure.
Sensing loops are routed through the fire zones
and are connected to fire and overheat detec-
tion control units in the cockpit. The detection
control units discriminate between valid fire
warnings and system faults. When either is de-
tected, the associated fire warning light will
illuminate in the cockpit.
The engine and APU fire-extinguishing systems
operate in a similar manner. Each system con-
sists of a fire-extinguishing (Firex) bottle that
is charged with Halon 1301 as an extinguish-
ing agent. It is pressurized by dry nitrogen, and
is discharged by electrically activated squibs.
The system is armed and activated manually
from the cockpit. In addition, the bottles are
guarded against overheat pressure explosion by
a thermal discharge port which will discharge
the bottle contents into the area around the
bottle installation. Firex bottle low-pressure
caution lights and test switches for the bottle
discharge squibs are located on the Firex mon-
itor panel on the copilot's side console.

FIRE DETECTION

GENERAL
All Challenger overheat and fire sensing loops
(left engine, right engine, APU, main landing
gear overheat, and the jet pipe/pylon over-
heat detection) operate in a similar manner.
Each system monitors the resistance of sens-
ing elements (loops) in its respective areas and
activates visual and aural warnings should
that resistance drop to a predetermined level
(trip point).
8-2 CL 601-3A/R
CL-600-2B16 PILOT TRAINING MANUAL
In addition, the systems detect failures in the
loops and will usually advise the flight crew
if a loop resistance falls to zero instantaneously,
such as might happen for a short circuit.

COMPONENTS

The fire detection system components (Figure
8-1) include sensing loops, detection control
units, FIRE lights, a fire bell, and the FIRE
WARN FAIL lights on the fire warning test
panel.
Fire Loops and Detection Units
Each fire-sensing loop (Figure 8-2) is a coax-
ial electrical wire consisting of two conductors,
a stainless steel outer conductor grounded to
the airframe, and an inner conductor connected
in a closed loop to a detection control unit. The
two conductors are separated by a semicon-
ductor medium which decreases in electrical
resistance as temperature increases. When the
resistance of the semiconductor decreases to
a preset limit, a fire warning is sent to the
flight compartment by one of the detection
control units. Three sensing-loop segments,
connected in series, are routed through the
powerplant fire zones. A single cable segment
is clamped to the inside of the APU enclosure.
There are three fire and overheat detection
control units, one for each powerplant and one
for the APU. Each unit contains two separate
alarm circuits to discriminate between valid fire
and overheat warnings and false warnings gen-
erated by sensing cable short circuits.
The units compare the speed and extent of the
sensing cable resistance change and initiate fire
and overheat warnings or fire fault warnings,
depending on the speed of the resistance
change. Thus, an abrupt change in resistance
which is usually caused by an electrical short
will be interpreted as a false fire and give a fire
fault indication. On the other hand, a true fire
normally changes insulator resistance at a
gradual rate, and, once the trip point is reached,
the fire detection control unit signals a fire
warning to the glareshield indicator.
FOR TRAINING PURPOSES ONLY
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