Engine fire detection and protection

Four procedures. The procedures in AF-M Procedures apply in full; this component covers what differs on the engine.

Procedure 0 — Safe the squib (R3)

Identical to AF-M Procedures Procedure 0, and it is not negotiable.

1. De-energize.
2. Disconnect the squib connector at the container.
3. Cap or short it per the manual.
4. Never apply an ohmmeter or a test set to a squib circuit unless the manual specifies the method and the instrument.

Check — point at the capped connector and say it aloud.

Procedure 1 — Inspect an engine fire detection system (S2–S4, S12, S14)

1. Trace the loop or sensor routing against the installation drawing. A loop rerouted for convenience no longer covers the zone it was designed for (PP-E Concepts §2).
2. Inspect the sensing element for chafe, kinks, crushing and corrosion — routed through a hot, vibrating compartment, this is where it fails.
3. Inspect support clamps at the specified intervals.
4. Check connectors and end fittings for security and corrosion.
5. Inspect thermal switches, thermocouples and flame detectors where fitted.
6. Look for heat damage to the element and its supports.

Check — compare the routing against the drawing, not against how you found it. Previous maintenance may have moved it.

Procedure 2 — Check detection system operation (S13, S5, S1)

1. Press-to-test first, and understand it proved the lamp and the warning circuit (AF-M Concepts §4).
2. Then perform the system operational check by the manual's method, which exercises detection itself.
3. Confirm the warning appears and clears.
4. Check any fault or short monitoring.
5. Record which check you performed.

Check — write down which test you did. "Fire system checked" is ambiguous, and the ambiguity lets a dead loop be signed off.

Procedure 3 — Inspect the extinguishing system (S6–S8, S10, S11, S2)

1. Procedure 0.
2. Hydrostatic test date on the container — out of date is unairworthy regardless of condition.
3. Cartridge date — cartridges have their own life.
4. Pressure against the temperature chart, not the gauge alone (PP-E Concepts §3).
5. Blowout plugs: thermal plug missing means an overheat discharge; discharge indicator missing means it was fired. Both are findings requiring investigation, not just replacement.
6. Inspect container mounting, discharge lines and nozzles for security and obstruction.
7. Inspect the discharge circuit wiring — by the manual's method only.
8. Reconnect the squib last.

Check — a missing blowout plug is a question, not a part number. Find out why it went before fitting a new one.

The checks, collected

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