Fourteen skills, one shared trainer, one absolute rule

Twenty-two elements. Ten of the fourteen skills are imagery and one is a lookup. The other three you perform in the shop, on the airframe systems trainer.

Most of the substance arrives from AF-M, which covers the same technology on the airframe. This unit adds the engine.

1. R3 — the rule, stated for the second time deliberately

Maintenance on circuits associated with electrically-activated squibs.

AF-M Concepts §1 states it in full: a squib is an explosive initiator, it needs very little current, and working the circuit with it connected risks discharging the bottle.

Disconnect and cap the squib before any work on the circuit. No exceptions.

The ACS states it twice — once for the airframe, once for the engine — and that repetition is deliberate. Do not let a cross-reference dilute it: this is the rule in this unit that has no judgment attached to it.

And GEN-K Concepts §4 is the mechanism most likely to catch you: an ohmmeter is a current source. It is the commonest way a bottle is fired by accident.

2. Fire zones are defined by what is in them

K1. A fire zone is not simply "the engine bay". Zones are classified by the combination of flammable fluid present, ignition sources present, and airflow — and the classification determines what detection and extinguishing provision is required.

That is why detection is where it is. Sensing elements are routed through the places a fire would start and would be detected earliest, not distributed evenly. A loop rerouted for convenience during maintenance is a detection system that no longer covers what it was designed to cover.

And it explains the difference between an overheat detector and a fire detector: an overheat detector responds to a sustained temperature rise, a fire detector to a rapid one. Different devices, different jobs, and a bleed-air leak sets off the first and not the second (PP-K §2).

3. Half the inventory is dates and temperature-corrected pressure

S10 cartridges, S11 hydrostatic test dates, S2 container pressure.

Identical to AF-M Concepts §3, and worth repeating for the same reason:

• A bottle in perfect condition is unairworthy on a date.
• Pressure means nothing without temperature. A bottle reading low on a cold morning may be correctly charged; one reading correct on a hot afternoon may be low. Read the chart.
• Blowout plugs tell you the history: a missing thermal plug means the bottle discharged from overheat; a missing discharge indicator means it was fired.

This is the fifth group of time-based airworthiness items in the certificate — with airframe fire bottles, ELT batteries, composite shelf life and life-limited parts. None of them can be inspected into serviceability.

4. The delivery result worth noticing

Fourteen skills and no apparatus. With AF-N and AF-O this is one of three subjects in the certificate needing no bench position at all, and it is what the delivery triage was built to find (our capital estimate).

What it does need is a component board: a continuous loop, a thermal switch, a thermocouple detector, a flame detector, a spent container with a cartridge, and blowout plugs. All salvage, all cheap, and shared with AF-M.

5. What consumes this unit

License

CC BY-SA 4.0 (Licensing).