Fire Protection
Fire and overheat detection, extinguishing systems and agents, and the engine fire handle logic.
Fire protection, summary notes
- DETECTION methods suit the zone: engine/APU zones use CONTINUOUS-LOOP (thermal) or spot thermal detectors sensing overheat/fire along their length; cargo and lavatories use SMOKE detectors (optical/ionisation); overheat detection warns before a fire.
- EXTINGUISHING: engine and APU fires are fought with fixed bottles of a gaseous agent (Halon 1301 or a modern replacement) discharged into the zone; cargo holds have knock-down and metered discharge; the cabin has portable extinguishers (water-glycol, BCF/Halon, CO₂).
- The FIRE HANDLE/switch for an engine both ISOLATES the zone, shutting off fuel, hydraulics and bleed air and tripping the generator, AND arms the extinguisher bottles; the engine is shut down before the agent is discharged.
- Systems distinguish a FIRE warning from a lesser OVERHEAT warning, and include a test facility to confirm detector and circuit integrity.
- Halon is a very effective agent because it chemically interrupts combustion, but is being replaced for environmental reasons.
- ⚠ Exam trap: a continuous-loop detector senses temperature along its WHOLE length (not one point); pulling the engine fire handle isolates fuel/hydraulics/bleed air to the zone and arms the bottle, always shut the engine down BEFORE discharging the extinguisher.
What sequence of things happens when the flight crew pull an engine fire handle?
Pulling the fire handle shuts down the engine's supplies to the fire zone, it closes the fuel shut-off valve, closes the hydraulic and bleed-air valves and trips the generator, cutting off what feeds the fire, and simultaneously arms the fire-extinguisher bottles so that rotating/pressing the handle discharges the agent into the now-isolated zone.
Fire protection concept map
Fire Protection
Fire protection quiz
Fire Protection, quiz
1. The detector shown runs right round the engine zone and back to the control unit. This arrangement is used because it:
Senses overheat anywhere along its lengthDetects only at its two endsMeasures fluid pressure2. A continuous-loop fire detector senses:
Temperature along its whole lengthOnly a single pointSmoke particles3. Cargo holds and lavatories are typically monitored by:
Smoke detectorsContinuous-loop thermal detectorsPitot probes4. A common fixed fire-extinguishing agent is:
Halon 1301 (or a modern replacement)Water onlyEngine oil5. Pulling the engine fire handle:
Isolates fuel/hydraulics/bleed air and arms the bottleOnly sounds a bellIncreases thrust6. The engine should be:
Shut down before discharging the extinguisherKept running during dischargeAccelerated during discharge7. An overheat warning differs from a fire warning in that it:
Warns of high temperature before an actual fireMeans the fire is outIndicates low oil8. 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 occurred