Airstart (All-Engine-Out Rapid Relight) from 10,000 FT to Sea Level requires what?

• A. FADEC rapid relight 200 KIAS for up to 15 Second Fuel Interruptions.
• B. FADEC rapid relight 180 KIAS for up to 20 Second Fuel Interruptions.
• C. FADEC rapid relight 210 KIAS for up to 10 Second Fuel Interruptions.
• D. FADEC rapid relight 190 KIAS for up to 25 Second Fuel Interruptions.

Answer: (A)

The main idea is understanding the FADEC rapid relight envelope for an all-engine-out airstart: you must have enough airflow to support light-off and keep the fuel interruption within a tight window so the ignition sequence can be reliable. For the CRJ-550, the specified condition is to start the rapid relight at 200 KIAS or higher and limit the fuel interruption to 15 seconds or less. Descending from 10,000 ft to sea level, you aim to reach that 200 KIAS to ensure adequate ram air and stable engine airflow for ignition, while keeping the fuel-off period short enough for a successful light-off. If you try the relight at a slower speed, airflow may be insufficient for reliable ignition; if you extend the fuel interruption beyond 15 seconds, the chance of a successful relight decreases due to cooling, fuel pressure decay, or compressor instability. The combination of 200 KIAS and up to 15 seconds best matches the FADEC’s relight capability and the engine’s light-off requirements in this scenario.