The same rules, in a hotter place

Twenty-nine elements. Most of the technique arrives from GEN-A and AF-K. What this unit adds is the environment, and the environment changes the consequences.

1. R4 — wiring near flammable fluid lines

Routing and security of wiring near flammable fluid lines.

AF-K Concepts §6 covers routing generally: never route wiring below a fluid line, keep separation, support at intervals, avoid chafe.

In an engine compartment the consequence is specific: a chafed conductor against a fuel or oil line is an engine fire.

And the compartment is the worst possible place for it — hot, vibrating, and full of both fuel and oil lines. Vibration that would take years to chafe through a cabin loom does it in months here.

So S1 — inspect engine electrical wiring, switches and protective devices — is a different task from its airframe equivalent despite nearly identical wording. What you look for:

• Separation from fluid lines, and wiring below a line is a finding, not a preference.
• Fire sleeve where the installation calls for it.
• Clamping interval, tighter than in the airframe because of vibration.
• The direction of any chafe — it tells you what is moving against what.
• Heat damage: hardened, cracked or discolored insulation near exhaust.

2. S9 — wire sizing, with a temperature penalty

AF-K Concepts §4 makes wire sizing the one design calculation in Airframe: current capacity sets a floor, acceptable voltage drop usually sets the actual size.

Here the same calculation carries a derating. A conductor's current capacity falls as ambient temperature rises, and an engine compartment runs far above cabin ambient.

So a wire correctly sized for the cabin is undersized in the cowling, and the tables have temperature columns for exactly this reason.

K8 — derating factors in switch selection — is the same idea applied to switches, which are also rated at an ambient temperature they will not see here.

3. R1 — polarity, and the failure that is immediate for once

R1 polarity, R2 external power, R3 energized circuits.

Most failures in this curriculum are delayed and invisible. Reversed polarity is not: connect a battery or a generator backwards and something fails immediately and expensively — diodes, regulators, avionics.

That makes it unusual and worth noting as such. The defense is procedural: confirm polarity before connecting, every time, and follow the manual's disconnect and reconnect order (GEN-F Procedures Procedure 2).

R3 — maintenance on energized circuits — is AF-K Concepts §3's rule. De-energize first, and in an engine bay that includes disconnecting the battery, because a starter circuit carries hundreds of amps and a spanner across it welds.

4. Alternators need excitation; generators do not

K1, K2, S5. The first question in troubleshooting a charging fault.

A generator produces output from residual magnetism — it will start generating on its own, which is why a generator can be "flashed" to restore residual field.

An alternator's field must be energized from the battery before it produces anything. So an alternator system that produces no output may have a perfectly good alternator and no field supply — a breaker, a switch, a regulator or a wire.

Check the field circuit before condemning the alternator. It is the commonest cause and the cheapest to fix.

5. Bonding at the engine

S13. The engine is a large metal mass mounted on rubber, which means it is electrically isolated from the airframe until it is bonded.

Without a bond: starter current returns through whatever path it can find — control cables, fuel lines, instrument lines — and current through a fuel line is exactly what nobody wants.

A bonding jumper is a structural-current path, not a signal ground, and it is measured (AF-I Procedures Procedure 3).

6. What consumes this unit

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