Fire Protection
Fire and overheat detection, extinguishing systems and the shut-down/isolate-before-discharge logic.
Fire protection, summary notes
- Engine and (where fitted) APU bays are protected by fire DETECTION, continuous-loop or spot thermal detectors, and fixed fire EXTINGUISHER bottles of a gaseous agent discharged into the isolated zone.
- The engine fire control isolates the zone, shutting off fuel and, as applicable, hydraulics/bleed to the bay, and arms/discharges the bottle; the engine is shut down before the agent is discharged.
- Overheat detection warns of a hot condition (e.g. a bleed leak) before a fire; the cabin carries portable extinguishers.
- A test facility confirms detector and circuit integrity; agents are Halon or a modern replacement.
- For the B1 technician the detectors, loops, warning circuits and bottle squibs are the key items.
- ⚠ Exam trap: a continuous-loop detector senses temperature along its whole length; on a fire the engine is shut down and the zone isolated (fuel off) BEFORE the extinguisher is discharged.
What must happen before the fire-extinguisher bottle is discharged into an engine bay?
The engine must be shut down and the supplies to the bay isolated, the fuel shut-off closed (and any hydraulic/bleed feeds cut), so the fire is no longer being fed. Only then is the bottle discharged, allowing the gaseous agent to smother the fire in the sealed zone rather than being blown through by continuing fuel/airflow.
Fire protection concept map
Fire Protection
Fire protection quiz
Fire Protection, quiz
1. A continuous-loop fire detector senses
Temperature along its whole lengthOne point onlySmoke particles2. Fixed engine-bay fires are fought with
A gaseous agent (Halon/replacement) bottleWaterEngine oil3. Before discharging the extinguisher, the engine is
Shut down and the zone isolated (fuel off)Kept runningAccelerated4. An overheat warning (not fire) most likely indicates
A hot condition such as a bleed leakAn actual fireLow oil quantity5. The fire-detection system includes a
Test facility to confirm detector/circuit integrityA fuel quantity gauge, so that a rapid loss of contents can be correlated with the warningA compass repeater, which allows the crew to record the heading at which the warning occurred6. Portable cabin extinguishers are
Emergency equipment for crew usePart of the engine bottleStructural members7. Two detection loops (A and B) are used so that
A single fault does not cause a false warning or lose detectionThe system is cheaper to install, since two simple loops cost less than one complex detectorOnly one loop is ever needed in service, the second being carried purely as a spare8. The extinguishing agent is discharged into the
Isolated fire zoneCabinFuel tank