When an engine shuts down in flight, the outer casing cools and shrinks faster than the hot internal turbine rotors. This differential thermal contraction can cause the stationary and rotating parts to bind together, preventing the engine from spinning freely. Pilots must maintain enough airspeed to keep the engine windmilling and prevent it from seizing before attempting a restart.
We had a dual flameout and lost the right side to core lock because we didn't keep the airspeed up.
The classic rookie mistake during a high-altitude flameout is pitching up to glide, which drops airspeed and lets the core stop spinning.
Related terms
Spool
A rotating assembly inside a gas turbine engine consisting of a compressor, a shaft, and a turbine.
Airspeed
The velocity of an aircraft relative to the air mass it is flying through.
Hard start
A damaging overpressure event or explosion that occurs when a rocket engine ignites with excess propellant in the combustion chamber.