Serious incident Boeing 747-151 N604US, Thursday 22 August 1991

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Date:	Thursday 22 August 1991
Time:	16:04 LT
Type:	Boeing 747-151
Owner/operator:	Northwest Airlines
Registration:	N604US
MSN:	19781/55
Year of manufacture:	1970
Engine model:	P&W JT9D-7A
Fatalities:	Fatalities: 0 / Occupants: 387
Other fatalities:	0
Aircraft damage:	Minor
Category:	Serious incident
Location:	Seattle, WA - United States of America
Phase:	En route
Nature:	Passenger - Scheduled
Departure airport:	Seattle, WA (KSEA)
Destination airport:	Tokyo (RJAA)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
THE NO 4 ENGINE CAUGHT FIRE DURING CLIMB AFTER TAKEOFF AND THE CREW ACTIVATED THE ENGINE FIRE EXTINGUISHER SYSTEM, DUMPED FUEL, AND RETURNED TO THE ARPT FOR AN EMERGENCY LANDING. THE NO 4 ENGINE FIRE AND A GRASS FIRE AT THE RWY T/D ZONE WERE EXTINGUISHED BY ARPT CFR CREW. AN EMERGENCY EVAC WAS CONDUCTED FROM THE LEFT SIDE AFTER THE ACFT STOPPED ON THE RWY. THE L5 EMERGENCY DOOR AND SLIDE FAILED TO DEPLOY FOR THE EVAC. EXAM OF THE ENGINE REVEALED EVIDENCE OF FUEL LEAK FROM THE MAIN FUEL CONTROL UNIT.

Probable Cause: A FIRE IN THE NUMBER 4 ENGINE, RESULTING FROM A FUEL LEAK AT THE MAIN FUEL CONTROL UNIT, DUE TO IMPROPER MAINTENANCE BY UNKNOWN/UNDETERMINED PERSON. THE L5 EMERGENCY EXIT FAILED TO OPERATEE DUE TO A BROKEN PLASTIC PULLEY GUARD IN THE SLIDE RELEASE MECHANISM.

Accident investigation: