Serious incident Boeing 747-251F N618US, Saturday 9 January 1988

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Date:	Saturday 9 January 1988
Time:	08:15 LT
Type:	Boeing 747-251F
Owner/operator:	Northwest Airlines
Registration:	N618US
MSN:	21122/269
Year of manufacture:	1975
Engine model:	P&W JT9
Fatalities:	Fatalities: 0 / Occupants: 3
Other fatalities:	0
Aircraft damage:	None
Category:	Serious incident
Location:	Minneapolis, MN - United States of America
Phase:	En route
Nature:	Unknown
Departure airport:	New York-John F. Kennedy International Airport, NY (JFK/KJFK)
Destination airport:	Seattle/Tacoma International Airport, WA (SEA/KSEA)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
AIRCRAFT EXPERIENCED A LOSS OF AILERON CTL WHEN ICE FORMED AROUND AILERON CONTROL CABLES AND RESTRICTED THEIR MOVEMENT. WATER DRAINING THROUGH OPEN PLENUM DRAINS IN THE MAIN LANDING GEAR WHEEL WELL FROZE WHEN EXPOSED TO BELOW FREEZING TEMPERATURES AT 35,000 FT. THE FLIGHT CREW WAS ABLE TO REGAIN LIMITED CONTROL BY USING VERY HEAVY CONTROL INPUTS. THE ACFT WAS LANDED UNEVENTFULLY AFTER DIVERTING TO THE NEAREST SUITABLE AIRPORT. MAINTENANCE PERSONNEL REPORTED THAT THE DRAINS WERE INADVERTENTLY LEFT OPEN.

Probable Cause:

Accident investigation: