What is the engine air restart envelope?

The engine air restart envelope refers to the specific conditions—primarily airspeed and altitude—under which the aircraft's engine can be successfully restarted in flight after a failure. The correct choice indicates that the engine air restart envelope is between 100-180 KIAS (Knots Indicated Airspeed) when operating below 30,000 feet Density Altitude (DA). This range is critical for successfully reinitiating engine operations after an engine shutdown, ensuring that the aircraft maintains a suitable speed and altitude for safe restart procedures.

In this scenario, the specified speed range helps prevent situations where the aircraft could stall or encounter unfavorable aerodynamic conditions that could complicate the restart process. Operating within this envelope allows for optimal airflow and engine performance necessary for a successful air restart. By including a limit on altitude (below 30,000 DA), the envelope takes into consideration how atmospheric conditions (like air density) impact engine performance.

The other choices either propose speeds outside this recommended range or reference altitudes that are not optimal for engine restart conditions, making them unsuitable for ensuring a safe restart of the aircraft's engine.