Core lock
Core lock is a jet engine failure that can happen on aircraft in flight, after an engine stops working for a period of time. When a jet engine has a flameout, the cooling air no longer circulates normally. If an aircraft is moving slowly, the sizes of some engine parts may change more quickly than others, such that they no longer fit together as designed. If this happens, the engine may seize. On an internal combustion engine that is not subject to extreme flight conditions, this may not be a problem. Since aircraft jet engines are built to exacting standards, however, core lock makes it difficult for pilots to perform either a windmill restart or an APU-assisted engine restart.
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 shutdown, 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
- NTSB Synopsis
- Air Line Pilots Association (ALPA)
- Popular Mechanics What Went Wrong: The Crash Of Flight 3701