Exhaust system inspection

Four procedures. The first is a screen; the second is the actual inspection.

Procedure 1 — Inspect a reciprocating engine exhaust system (S1, S3)

1. Allow it to cool. Exhaust components stay hot far longer than they look.
2. Clean enough to see cracks — soot hides them.
3. Inspect the known crack sites specifically: welds, slip joints, clamps, supports, changes of section, bends (PP-L Concepts §3).
4. Look for soot streaks and staining, which mark existing leaks.
5. Check clamps and supports: security, correct type, correct torque, and no cracked or distorted brackets.
6. Check slip joints for wear, galling and correct engagement.
7. Inspect surrounding structure and wiring for heat damage and discoloration.

Check — look for soot streaks before looking for cracks. A leak marks itself, and the mark is easier to see than the crack that made it.

Failure — inspecting a sooty system without cleaning it. The soot is hiding exactly what you are looking for.

Procedure 2 — Perform a pressure leak check (S7)

This is the inspection. Procedure 1 is the screen (PP-L Concepts §2).

1. Remove the system, or seal it in place, per the manual's method.
2. Block the outlets as the procedure specifies.
3. Apply the specified low pressure — and only the specified pressure. Exhaust components are thin and over-pressure will damage them.
4. Find leaks by the specified method — soapy solution, or immersion where permitted.
5. Mark every leak found and assess against the manual.
6. Any crack in an exhaust component within a heat shroud is a rejection unless the manual explicitly permits a repair.

Check — do this on any system feeding a cabin heat exchanger, at the interval the manual specifies and after any finding. It is the only test that positively demonstrates integrity.

Procedure 3 — Inspect a heat exchanger and its shroud (S5)

Cross-referenced to AF-G Procedures Procedure 4 — the same task, from the engine side.

1. Remove the shroud so the exhaust component inside is fully accessible.
2. Clean and inspect all round, including the surfaces the shroud covered.
3. Inspect welds and slip joints with light and magnification.
4. Pressure leak check (Procedure 2).
5. Inspect the shroud for security, condition and sealing.
6. Check the ducting to the cabin for condition and security.

Check — the shroud must come off. An inspection with the shroud fitted has not looked at the part that matters (PP-L Concepts §1).

Procedure 4 — Inspect internal baffles (S4)

1. Inspect through the outlet with a light, and by borescope where the manual permits.
2. Listen and feel: with the system cool and detached where possible, a rattle or a shifting weight indicates broken internal parts.
3. Check for restriction — anything visible obstructing the flow path.
4. Inspect for material that has migrated into the outlet or the tailpipe.

Check — shake it, if it can be removed. A muffler with a broken baffle rattles, and that is the fastest indication of a fault that is otherwise invisible.

Failure — assessing a muffler by its outside. It tells you almost nothing about its inside (PP-L Concepts §2).

The checks, collected

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