Fire Protection
Fire and overheat detection, extinguishing systems and agents, and the engine fire handle logic.
Fire protection, summary notes
- DETECTION suits the zone: engine/APU zones use CONTINUOUS-LOOP (thermal) or spot thermal detectors sensing overheat/fire along their length; cargo holds 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 isolated zone; cargo holds have metered discharge; the cabin has portable extinguishers.
- The engine FIRE HANDLE 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.
- For the B2 technician the detection loops, warning circuits, indication and test logic are the focus.
- ⚠ Exam trap: a continuous-loop detector senses temperature along its WHOLE length; pulling the engine fire handle isolates fuel/hydraulics/bleed air and arms the bottle, always shut the engine down BEFORE discharging the extinguisher.
How does the system tell the difference between an overheat and a fire, and why does it matter?
Detection elements/loops are set to trigger an OVERHEAT caution at a lower temperature threshold and a FIRE warning at a higher one (or via separate loops). The overheat alert lets the crew act, e.g. shut a leaking bleed duct, before a fire develops, whereas a fire warning demands the full engine fire drill. Distinguishing them avoids an unnecessary engine shutdown for a mere overheat.
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 onlySmoke2. Cargo holds and lavatories use:
Smoke detectorsThermal loops onlyPitot probes3. A common fixed extinguishing agent is:
Halon 1301 (or a replacement)Water onlyEngine oil4. Pulling the engine fire handle:
Isolates fuel/hydraulics/bleed air and arms the bottleOnly sounds a bellIncreases thrust5. The engine should be:
Shut down before discharging the extinguisherKept running during dischargeAccelerated6. An overheat warning:
Warns of high temperature before an actual fireMeans the fire is outIndicates low oil7. The fire-detection system includes a:
Test facility for detector/circuit integrityFuel gaugeCompass8. Halon is being phased out because it is:
Environmentally harmfulToo cheapNon-flammable