Serious incident Boeing 757-222 N551UA,
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ASN Wikibase Occurrence # 370424
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Date:Saturday 11 January 2003
Time:02:45 LT
Type:Silhouette image of generic B752 model; specific model in this crash may look slightly different    
Boeing 757-222
Owner/operator:United Airlines
Registration: N551UA
MSN: 25339/484
Year of manufacture:1992
Total airframe hrs:41261 hours
Engine model:Pratt & Whitney PW 2037
Fatalities:Fatalities: 0 / Occupants: 140
Aircraft damage: Minor
Category:Serious incident
Location:Salt Lake City, UT -   United States of America
Phase: En route
Nature:Passenger - Scheduled
Departure airport:San Francisco International Airport, CA (SFO/KSFO)
Destination airport:Boston-Logan International Airport, MA (BOS/KBOS)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
The passenger jet was at a cruise altitude of 37,000 feet msl and approximately 95 nautical miles south of Salt Lake City (SLC), when a flight attendant called from the aft cabin and stated there was a fire in the left aft lavatory, and that another flight attendant was fighting the active flames with a Halon extinguisher. The captain declared an emergency, requested priority handling for landing at SLC, and made an uneventful landing. An examination of the airplane revealed the lavatory toilet water level sensor was charred and melted. On further examination, the top left corner of the circuit board in the sensor was melted and consumed. Portions of several wires that had solder attachments to the circuit board at the melted area, including a 115-volt AC input wire and a 28-volt DC ground wire were melted and consumed. The left side of the circuit relay, adjacent to the consumed area of the circuit board, was melted and had melted solder on its exterior. The left hexagon-shaped screw, one of the two screws that mount the relay to the circuit board, was also melted. The manufacturer determined the melting point of the screw was between 2,550 and 2,650 degrees F. The investigation team determined that for these temperatures to occur, one of the wires in the area of the left screw would have had to arc.

Probable Cause: the arcing wires in the lavatory sensor that resulted in the subsequent fire.

Accident investigation:
Investigating agency: NTSB
Report number: DEN03IA033
Status: Investigation completed
Duration: 10 months
Download report: Final report




Revision history:

25-Mar-2024 10:34 ASN Update Bot Added

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