On January 9, 1988, a Boeing 747-251F (registration N618US) operated by Northwest Airlines was involved in an aviation accident near Minneapolis, MN. Investigators recorded the probable cause as: Ice formed around aileron control cables, restricting their movement, caused by water draining through open plenum drains that froze at altitude. The drains were inadvertently left open by maintenance personnel. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 13 related events involving the same aircraft type or operator are linked below.
An aircraft experienced a loss of aileron control when ice formed around control cables. Water from open plenum drains froze at 35,000 ft. The crew regained limited control and landed after diverting.
Incident Description
An aircraft experienced a loss of aileron control during flight. Investigation revealed that ice had formed around the aileron control cables, restricting their movement. The ice formed when water draining through the plenum drains in the main landing gear wheel well froze upon exposure to below-freezing temperatures at 35,000 feet. The plenum drains had been inadvertently left open by maintenance personnel.
The flight crew was able to regain limited control of the ailerons by applying very heavy control inputs. The aircraft was diverted to the nearest suitable airport and landed without further incident.
Probable cause
Ice formed around aileron control cables, restricting their movement, caused by water draining through open plenum drains that froze at altitude. The drains were inadvertently left open by maintenance personnel.
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