Fire Protection - Engines

Amendment: APU bleed air valve closed when Left Fire Switch pulled.

Engine Fire Protection

Engine Fire Protection consists of these systems:

Engine Fire and Overheat Detection

Fire and Overheat Detectors.

There are dual detector loops in each engine nacelle to provide both fire and nacelle overheat detection. In addition, each engine has dual detector loops for:

Turbine Overheat Detection

Each engine has dual turbine overheat detectors which sense the cooling air from the main bearings and turbine discs. Turbine overheat detection will produce an engine FIRE warning.

Nacelle Overheat Detection

The nacelle overheat detectors are installed behind the precooler air inlets, in the pneumatic ducting area.

Dual Detection Systems

Dual detection is provided to reduce the chance of false warnings. Two detectors located together will both be activated by a fire/overheat. If both detectors are activated the fire warning will operate. If a fault activates one detector it will be displayed as a fault. (i.e. STATUS message) If subsequently, a fire/overheat is sensed the remaining detector will provide the fire warning.

In normal operation, both loops must sense the fire or overheat to activate the fire warnings or overheat cautions. The engine fire loops are continuously monitored for faults. When a fault is detected in one of the loops, the systems reconfigures itself for single loop operation. When the good loop senses a fire/overheat condition, the appropriate fire warnings or overheat cautions activate. If both loops indicate a fault, a fire warning is activated.

The SYSTEM FAIL light illuminates and the EICAS advisory message FIRE/OVHT SYS displays to indicate failure of the fire/overheat detection system. An EICAS status message indicates the inoperative loop. The SYSTEM FAIL light and advisory message can be reset to allow monitoring of the remaining systems.

Strut and Turbine Overheat detectors do not have fault outputs so both loops must generate an overheat signal for the system to activate.

Engine Fire Warning

The indications of an engine fire warning are:

The fire warning lights remain illuminated as long as the fire signal exists. The fire bell may be silenced by any of the following actions:

The fire warning bell rings intermittently for 2 seconds on, then 3 seconds off.

Engine Overheat Caution

The indications of an engine overheat caution are:

The overheat lights remain illuminated as long as the overheat condition exists.

Engine Fire Extinguishing

Engine Fire Extinguishing

There are two engine fire extinguisher bottles. Either or both bottles can be discharged into either engine.

When the fire switch is pulled out:

AMM When the Left engine fire switch is pulled out, the APU Bleed Air Valve is commanded closed, irrespective of the position of the APU Bleed Air Valve switch.

Rotating the fire switch in either direction discharges a single extinguisher bottle into the associated engine. Rotating the engine fire switch in the other direction discharges the remaining extinguisher bottle into the same engine.

If an extinguisher bottle is discharged or has low pressure:

Engine/APU Fire and Override Switches

Engine/APU Fire and Override Switches The Engine and APU Fire Switches are mechanically locked in the down position to avoid inadvertent activation. When a fire is detected, the respective switch is electrically unlocked and may then be pulled out. Manual unlocking of the switch is accomplished by pushing the fire override switch located beneath the Fire Switch.