Flight History
The cargo plane had arrived at Montreal-Dorval International Airport following a flight from Dayton, Ohio. After unloading all cargo, it departed Montreal at 09:58 for Ottawa under an instrument flight rules flight plan. The en route phase was uneventful.
Accident Sequence
At approximately 10:19, while cruising at 3,000 feet at about 200 KIAS, the flight data recorder showed a full-up deflection of the left aileron and a full-down deflection of the right aileron. The aircraft began a high-rate roll to the left. The right aileron remained fully deflected for three seconds, then its deflection gradually decreased by about five degrees over the next seven seconds. The left aileron stayed nearly fully deflected for the first eight seconds, then decreased by about five degrees over two seconds. By that time, the aircraft had rolled through approximately 460 degrees, with the nose dropping 20 to 30 degrees below the horizon. The ailerons then suddenly returned to near neutral and remained there for the last three seconds of flight. The aircraft maintained a left bank of about 90 degrees and recorded a maximum vertical g of 4.7. It struck the ground at about 290 KIAS after a heading change of approximately 75 degrees left of the cruise heading. At impact, the bank angle was nearly 90 degrees left and the pitch angle was 41 degrees down. The time from initial aileron deflection to ground impact was about 18 seconds. Both pilots were killed.
Investigation Findings
The official investigation determined that the aileron control system was asymmetrically rigged, making it susceptible to aerodynamic overbalance. The operator had not conducted required post-maintenance flight tests of aileron control response. After a large control-wheel input by the pilot, the ailerons were held at full deflection by aerodynamic forces, and the pilot's subsequent control reaction was inappropriate. Contributing factors included the design of the aileron system, ambiguous and incomplete maintenance instructions, a lack of published information for flight crew about aileron system performance and possible emergencies, and factors that may have led to the development of flight crew fatigue.