Definition
A condition in a turbine engine in which the rotating core (compressor and turbine assembly) seizes and cannot turn after a hot shutdown, caused by the hot rotor components contracting against the cooler, slower-cooling outer case and binding internally. The engine becomes immovable until the temperatures of the rotor and case equalise.
Plain English
After certain turbine engine shutdowns, the inside spinning parts cool faster than the outer casing, and the tight clearances cause everything to lock up so the engine won't turn. It frees itself once the temperatures even out.
Context Anchor
Encountered in turbine engine operation, especially during starting, shutdown, and troubleshooting after a hot shutdown.
Derivation
Core' refers to the engine's central rotating assembly (the gas generator core), and 'lock' describes the mechanical seizure. The term is descriptive: the core literally locks up.
Why Pilots Care
Can delay or prevent engine restart, requiring a cooling period before another attempt.
Grounding Statement
Core lock means the engine’s main spinning section is stuck when it should be able to rotate.
Intuition Check
Core lock does not mean the engine is locked by a switch, key, or electronic system. It means the engine’s internal rotating parts are physically unable to turn freely.
Example Sentence 1
After the rapid hot shutdown, the crew suspected core lock and held off attempting a restart until the engine had cooled.
Example Sentence 2
Maintenance confirmed core lock by noting the engine would not turn by hand until it cooled.