Core lock
Core lock is a jet engine failure that can happen on aircraft in flight, during deep stalls. When an aircraft stalls deeply, the airflow to the engine becomes turbulent, and causes parts to cool unevenly. Since metal expands when heated and shrinks when cooling, the sizes of the engine internals may change more than others. If the difference in sizes change enough, some parts will grip onto other parts and cause the engine to seize, or abruptly stop. This condition is called “core lock”.
Core lock makes it difficult for pilots to perform either a windmill restart or an APU-assisted engine restart.
When the engine parts’ temperature is allowed to normalize, due to the airflow becoming normal, which in turn is caused by the aircraft recovering from the stall, the part sizes could normalize and allow the engine to be restarted.
Pinnacle Airlines Flight 3701[]
Core lock was cited as one of the contributing causes to the October 2004 Pinnacle Airlines Flight 3701 accident, noting that the primary cause, the pilots' "unprofessional ... deviation from standard operating procedures" causing both engines to shut down, was exacerbated by:
the pilots' failure to achieve and maintain the target airspeed in the double engine failure checklist, which caused the engine cores to stop rotating and resulted in the core lock engine condition. Contributing to this accident was 1) the engine core lock condition, which prevented at least one engine from being restarted, and 2) the airplane flight manuals that did not communicate to pilots the importance of maintaining a minimum airspeed to keep the engine cores rotating.
References[]
- Aviation risks
- Jet engines