Alitalia Airlines Flight 604

The flight was at cruise altitude when the flight crew discovered that they were unable to move the control wheel for lateral (aileron) control. The rudder and elevator flight controls remained free for movement. As the flight neared its destination, the crew tried to extend with wing flaps. The leading edge slats extended, but they were unable to extend the trailing edge wing flaps. The flight landed in that condition. Post flight examination of the airplane revealed ice accumulations in all three wheel wells. The ice had accumulated on the aileron control cables, and flap extension cables, and prevented cable movement. The ice was traced to a water leak in the potable water system where a rubber hose attached to a water line fitting, under the floorboard, near the 3R door. When the floorboard in the area was lifted, upward movement of the floorboard was restricted by the rubber hose water line that was attached to the underside of the floor board. Water was observed misting from the line where it attached to the fitting. When the floorboard was lifted further, the water line pulled loose from the fitting, and water flowed out. Examination of the rubber water hose revealed it failure was due to excessive load applied to the crimped joint between the flexible hose and it end fitting. The airplane manufacturer had attached water lines to the underside of the floorboards. The airplane maintenance manuals did not contain any information about how to know if a water line was connected to the underside of a floorboard, or for disconnecting water lines attached to the underside of the floorboards prior to lifting them. There was no jammed flight control checklist in effect at the time of the incident. QAR data revealed the pilots had limited movement with the of the ailerons with the auto-pilot engaged or disengaged through roll control wheel steering (RCWS), a customer selected option for the airplane.

Verbatim NTSB analysis and probable cause from the NTSB dataset