NTSB Identification: CHI95IA028.
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Incident occurred Wednesday, November 02, 1994 in CHICAG0, IL
Probable Cause Approval Date: 03/27/1995
Aircraft: BOEING 747-251B, registration: N631US
Injuries: 3 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

THE FLT CREW DISCONNECTED THE NUMBER ONE ENG CONSTANT SPEED DRIVE (CSD) DURING A FLT ON THE DAY PRIOR TO THIS INCIDENT WHEN ITS OIL PRESSURE LIGHT ILLUMINATED. DUE TO OTHER, UNRELATED MAINTENANCE, THE AIRPLANE'S NEXT REVENUE FLT WAS CANCELLED. SECOND SHIFT MECHANICS WERE ASSIGNED MAINTENANCE ON THE AIRPLANE. THE MECHANICS DECIDED TO TROUBLESHOOT THE UNIT. THE CSD WAS MECHANICALLY RECOUPLED AND THE ENG WAS STARTED. AFTER THE ENG START, THE START VALVE LIGHT FAILED TO GO OUT AND THE ENGINE WAS SHUT DOWN. A MECHANIC REMOVED THE MAIN CSD WIRING HARNESS CANNON PLUG TO HELP WITH THE TROUBLE SHOOTING PROCESS. THE START VALVE WAS REPLACED AND THE ENG WAS RUNUP. THE CSD CANNON PLUG WAS NOT CONNECTED AT THE CONCLUSION OF THE ENG RUNUP. AFTER SHUTDOWN THE START VALVE CHANGE WAS ENTERED INTO THE AIRPLANE MAINTENANCE RECORDS. THE MECHANIC WHO RECOUPLED THE CSD INFORMED THE LEAD MECHANIC OF HIS ACTION BEFORE HE LEFT FOR THE DAY. ACCORDING TO THE COMPANY, THE THIRD SHIFT MECHANICS DID NOT HAVE ENOUGH TIME TO CHANGE THE CSD. THE NUMBER ONE ENG WAS '...CLOSED UP [AND] THE AIRCRAFT WAS DISPATCHED.' DURING TAXI FROM LANDING THE CSD CAUGHT FIRE.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

inattentive maintenance service of the airplane by the mechanic who failed to disengage the constant speed drive (CSD) after the engine runup had been completed. A factor in this incident was the lead mechanic not performing maintenance record keeping after being informed that the CSD had been recoupled.

Full narrative available

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