AIRPLANE
OPERATIONS
MANUAL
FIRE PROTECTION
JANUARY 21, 2002
2-07-10
Page
1
Code
01
ENGINE AND APU FIRE PROTECTION SYSTEM
FIRE/OVERHEAT DETECTION
The engines and the APU are protected against the occurrence of fire
by means of fire detection and fire extinguishing systems.
Essential DC bus 1 powers the engine 1 fire detection system and
essential DC bus 2 powers the engine 2 and the APU fire detection
system. Hot battery bus 1 and 2 power the engine fire extinguishing
system, whereas the APU fire extinguishing system is powered by
essential DC bus 2.
The fire/overheat detection system is provided with independent
sensor tubes installed in the engines and APU. The sensor tube
contains a fixed volume of inert gas (Helium) and a gas-impregnated
(Hydrogen) core material. The inert gas provides sensing of
overheating. The core element provides sensing of localized fire or
high-intensity heating. Overheating causes the sensor tube’s internal
gas pressure to increase. This closes a switch on the fire/overheating
detection system’s electrical circuit and activates the warning system.
Localized fire or high-intensity heating increases the central core’s gas
volume, raising the sensor tube’s internal pressure, thus activating the
alarm switch in the same manner as described above.
Manual resetting of the fire detection system is not available. Upon
removal of the fire or overheat condition, a reversible process takes
place, and the system automatically returns to the normal standby
operation mode.
An integrity switch continuously monitors the sensor tube’s integrity.
The integrity switch is held closed by the sensor’s internal pressure.
Should this pressure be lost the integrity switch opens, generating a
signal to indicate that the system is inoperative.
Upon detection of a fire/overheat signal in the engine or APU, the
associated handle (for the engines) illuminates, an aural warning is
generated and a warning message is presented on the EICAS. The
visual warning remains activated as long as the fire signal exists. The
aural warning may be canceled by pressing the master warning light.
In the case of failure of any fire detector, a caution message is
presented on the EICAS.
The APU fire detection system provides a signal to shut down the APU
automatically in case of fire warning during ground operation.
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