In-Flight Relight — Windmill / Starter-Assisted Relight and the Envelope

After a shutdown, this article covers the relight: three methods (starter-assisted / windmill quick / stabilised windmill), the relight envelope (speed–altitude zones), and the windmill relight procedure. It is the key step in all-engines failure.

1. The relight envelope — three zones

Per the engine-relight-envelope chart (speed on the horizontal, FL on the vertical):

[!note]- The three-zone logic (chart + from 07) The faster the aircraft, the higher the windmill speed, the better it self-rotates: low speed needs the starter (①); mid speed just after shutdown (≤ 30 s) allows a quick windmill relight (②); high speed self-rotates for a stabilised windmill relight (③) (echoing 07's "in the stabilised windmill zone the start valve does not open"). The ≤ 30 s condition for ② is because the speed is still high just after shutdown.

2. Windmill relight procedure

If engine relight can be attempted: ENG START sel ... IGN / START. Approaching or below FL 300: Windmill Relight — ALL ENG MASTERS ... OFF 30 S THEN ON. ENGs RELIGHT ... TRY REGULARLY. Windmill relight attempts can be repeated until successful...

Per PRO-ABN-ENG: ENG START selector → IGN/START; approaching or below FL 300, Windmill Relight — ALL ENG MASTERS OFF 30 s THEN ON; ENGs RELIGHT — try regularly; repeatable until successful.

3. Starter-assisted relight

At low speed (windmill speed insufficient) the starter assists (the manual start / starter of 07). The starter's bleed demand links to APU bleed / bleed availability (31 attempts windmill first without APU bleed, then with it).

4. Relight decision and counterintuitive points

 Can relight (no damage, [20](./ata-70-20-engine-failure.md))?
   │ read the relight envelope (speed–altitude)
   ├─ high speed → stabilised windmill relight (③, no starter)
   ├─ mid speed + just shut down (≤ 30 s) → windmill quick relight (②)
   ├─ low speed → starter-assisted relight (①)
   └─ windmill procedure: ENG START IGN/START, below FL 300 ALL ENG MASTERS OFF 30 s THEN ON, try regularly

[!warning]- At high speed the windmill self-rotates — no starter needed The faster the aircraft, the higher the windmill speed → at high speed (③ stabilised windmill zone) it relights without the starter (chart + 07). Only low speed needs the starter (①).

[!warning]- Windmill quick relight needs "just shut down (≤ 30 s)" Zone ② requires a shutdown time ≤ 30 s (chart) — the speed is still high just after shutdown for a quick relight; if it has been longer the speed has decayed and you drop to ① starter-assisted, or adjust speed.

Self-test

[!note]- Q1. The three in-flight relight methods? ① STARTER ASSISTED (low speed) ② WINDMILL QUICK RELIGHT (mid, shutdown ≤ 30 s) ③ STABILIZED WINDMILL RELIGHT (high speed).

[!note]- Q2. Why is no starter needed at high speed? High speed → high windmill speed → self-rotation relights (stabilised windmill zone).

[!note]- Q3. The ENG MASTER action for a windmill relight? ENG START → IGN/START; below FL 300, ALL ENG MASTERS OFF 30 s THEN ON, try regularly.

[!note]- Q4. Why does zone ② need shutdown ≤ 30 s? Just after shutdown the speed is still high for a quick relight; longer and the speed decays, dropping to starter-assisted or needing a speed change.

Key takeaways

References

• Engine-relight-envelope chart (FCOM) — three zones: ① starter-assisted ② windmill quick (≤ 30 s) ③ stabilised windmill (speed–altitude).
• FCOM PRO-ABN-ENG — windmill relight: IGN/START, below FL 300 ALL ENG MASTERS OFF 30 s THEN ON, try regularly.
• FCOM DSC-70-80-30 (07) — start valve does not open in the stabilised windmill zone (high-speed windmill self-rotation).

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.