NTSB Identification: SEA91IA081.
The docket is stored on NTSB microfiche number 44378.
Scheduled 14 CFR operation of UNITED AIRLINES
Incident occurred Tuesday, April 09, 1991 in SEATTLE, WA
Probable Cause Approval Date: 05/05/1993
Aircraft: BOEING 737-222, registration: N9003U
Injuries: 2 Minor,31 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.

DURING THE INITIAL CLIMB, THE FLIGHT CREW HEARD A LOUD BANG FOLLOWED BY AIRFRAME VIBRATIONS. THE CREW WAS NOTIFIED BY THE CONTROL TOWER THAT SMOKE AND FLAME WERE EMITTING FROM THE LEFT ENGINE. THE FLIGHT CREW DECLARED AN EMERGENCY AND WAS CLEARED TO LAND. THE PILOT DISCHARGED A BANK OF FIRE EXTINGUISHING AGENT AND SHUT THE ENGINE DOWN. THE FLIGHT LANDED WITHOUT FURTHER INCIDENT. DURING THE FOLLOW-UP INVESTIGATION, IT WAS FOUND THAT A TURBINE BLADE FAILED IN FATIGUE. THE FLIGHT CREW HAD RECEIVED AN INDICTION THAT THE FIRE EXTINGUISHING AGENT HAD DISCHARGED, HOWEVER, IT WAS LATER FOUND THAT IT DIDN'T DUE TO THE INSTALLATION OF AN INCORRECT DISCHARGE OUTLET. THE REAR EMERGENCY SLIDE ON THE RIGHT SIDE WAS SLOW IN INFLATING AND WAS NOT USABLE FOR THE EVACUATION. THE SLIDE WAS INSTALLED ON A TEST STAND AND FOUND TO OPERATE WITHIN NORMAL OPERATING PARAMETERS.

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

TURBINE BLADE FAILURE FROM FATIGUE. FACTORS TO THE INCIDENT WERE INOPERATIVE ENGINE FIRE EXTINGUISHER, INADEQUATE SERVICE OF AIRCRAFT AND DELAYED DEPLOYMENT OF EMERGENCY SLIDE.

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