Engine Stall / Surge — Symptoms, FADEC Auto FUEL ADJUSTED, Handling Branches

Air Bleed gave the stall-margin tools (VSV angling + IP8/HP3 bleed). This article covers what happens when that margin is lost — a compressor stall/surge: how to recognise it, the Trent-specific FADEC auto FUEL ADJUSTED, and the parameter-check handling branches. A surge is a flow instability that can spike EGT and lose thrust.

1. Stall symptoms

A stall may be indicated by varying degrees of abnormal engine noises, accompanied by flame from the engine exhaust (and possibly from engine inlet in severe cases), fluctuating parameters, sluggish or no thrust lever response, high EGT and/or a rapid EGT rise when thrust lever is advanced. Engine stalls must be reported for maintenance action.

Per PRO-ABN-ENG, a stall shows as abnormal engine noises + flame from the exhaust (and possibly the inlet in severe cases) + fluctuating parameters + sluggish or no thrust-lever response + high EGT and/or a rapid EGT rise on advancing the lever. Stalls must be reported for maintenance.

[!note]- A stall = the stall margin (08) lost or exceeded (synthesis) 08's VSV (angling) + IP8/HP3 bleed (low-speed dumping) hold the stall margin; when it is breached (FOD, icing, abrupt handling, a component fault) the compressor flow destabilises and reverses → stall. The "flame from the exhaust" is the gas reversing.

2. FADEC auto FUEL ADJUSTED (Trent-specific)

If stall detected by FADEC: In flight: For aircraft equipped with RR engines: FUEL ADJUSTED — Fuel/Air ratio is automatically decreased until the stall disappears.

Per PRO-ABN-ENG, on a FADEC-detected stall in flight (RR engines), the Fuel/Air ratio is automatically decreased until the stall disappears — the Trent's FADEC tries to clear the stall first, with no prior crew action.

3. Crew handling branches

THR LEVER (AFFECTED ENGINE) ... IDLE. ENG PARAMETERS (AFFECTED ENGINE) ... CHECK. If abnormal ENG parameters: ENG MASTER (AFFECTED ENGINE) ... OFF (Note: If the flight crew suspects that the stall was transient, they can consider an engine relight). If normal ENG parameters: ENG ANTI-ICE (AFFECTED ENGINE) ... ON; WING ANTI-ICE ...

Per PRO-ABN-ENG: THR LEVER (affected) IDLE (reduce thrust to ease the stall), then CHECK ENG parameters:

• abnormal → ENG MASTER OFF (shut down; if the stall is suspected transient, a relight may be considered).
• normal → ENG ANTI-ICE (affected) ON + WING ANTI-ICE.

[!note]- Why anti-ice when the parameters are normal (synthesis) Normal parameters (the engine is still usable) → the stall may be from ice disturbing the intake → engine + wing anti-ice clears it and restores the intake flow field. Abnormal parameters (the engine is damaged) → shut down directly. This branches on "is the stall a reversible disturbance or real damage?"

4. Handling framework and counterintuitive points

 stall symptoms (noise / flame / fluctuating parameters / EGT rise)
   │ FADEC auto FUEL ADJUSTED (RR, decrease Fuel/Air ratio)
   ▼ THR LEVER (affected) IDLE → CHECK ENG parameters
   ├─ abnormal → ENG MASTER OFF (if transient suspected, relight → 21)
   └─ normal → ENG ANTI-ICE ON + WING ANTI-ICE (icing cause suspected)
 must report for maintenance

[!warning]- The Trent FADEC decreases Fuel/Air ratio first to clear the stall On an RR engine the FADEC, on detecting a stall, automatically FUEL ADJUSTED (decreases Fuel/Air ratio until the stall disappears) (PRO-ABN-ENG); the crew then THR IDLE + check parameters. It is not all manual.

[!warning]- Normal parameters → anti-ice — a stall can be ice-induced The normal-parameter branch is ENG + WING ANTI-ICE ON (PRO-ABN-ENG) — treating the stall as a reversible intake disturbance (icing); only abnormal parameters lead to shutdown.

Self-test

[!note]- Q1. Stall symptoms? Abnormal noises + flame from exhaust (inlet in severe cases) + fluctuating parameters + sluggish/no thrust-lever response + high EGT/rapid rise.

[!note]- Q2. What does the Trent FADEC do on a detected stall? FUEL ADJUSTED: Fuel/Air ratio automatically decreased until the stall disappears (RR engines, in flight).

[!note]- Q3. The two branches after THR IDLE + parameter check? Abnormal → ENG MASTER OFF (transient suspected → relight possible); normal → ENG ANTI-ICE ON + WING ANTI-ICE.

[!note]- Q4. Why anti-ice when parameters are normal? The stall may be from ice disturbing the intake → anti-ice restores the intake flow (normal parameters = engine still usable).

Key takeaways

References

• FCOM PRO-ABN-ENG — stall symptoms; FADEC auto FUEL ADJUSTED (RR); THR IDLE + parameter-check branches (abnormal MASTER OFF / normal ANTI-ICE ON); must report for maintenance.
• FCOM DSC-70-70 (08) / DSC-70-10-10 (01) — stall-margin background (VSV + IP8/HP3 bleed).

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.