Turbine air systems

Four procedures. Both station elements are performed on a static article (PP-B Procedures Procedure 0 applies).

Procedure 1 — Identify cooling airflow (S3, S2)

1. Trace the primary gas path first (PP-B Procedures Procedure 1).
2. Now trace the secondary flows: where cooling air is bled from, where it goes, and where it rejoins or exhausts.
3. Identify insulation blankets and shrouds and say what each is protecting.
4. Identify cooling ducting and its route.
5. Identify bearing cavity sealing air.

Check — name what each secondary flow is protecting. "Cooling air" is not an answer; which component, and from what, is.

Procedure 2 — Inspect cooling ducting and blankets (S4, S2)

1. Inspect ducting for security, damage, collapse, chafe and correct routing.
2. Inspect insulation blankets for damage, saturation with fluid, displacement and security. A saturated blanket is a fire risk as well as a failed insulator.
3. Check clamps and standoffs.
4. Look for evidence of heat where there should not be any — discoloration on structure or wiring near the engine.

Check — discoloration on nearby structure means heat is escaping somewhere it should not be. Find where before replacing the blanket.

Procedure 3 — Inspect a particle separator (S7)

1. Inspect for erosion of the separating surfaces — that is its job and it wears.
2. Check the scavenge path is clear.
3. Check security and sealing — a leak past the separator lets unfiltered air straight into the compressor.
4. Inspect for damage or distortion that would change the flow path.

Check — a separator that leaks past its seal is worse than none, because it costs performance and provides no protection.

Procedure 4 — Inspect and check a bleed air system (S8, R1)

1. Engine shut down and cool. Bleed air burns (PP-K Concepts §2).
2. Inspect ducting, joints and clamps for leaks — soot, discoloration, or a clean streak where hot air has scoured.
3. Check valve condition and actuation where accessible.
4. Check overheat detection associated with the bleed system where fitted (AF-M).
5. Perform the functional check by the manual's method.

Check — look for a clean streak. A bleed leak scours the area around it clean, and that stripe is often the only visible sign.

Failure — searching for a bleed leak on a running engine by hand. The air is clear, very hot and under pressure, and it will cut you before you feel it.

The checks, collected

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