This December 2007 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Aircraft: Beech Duke. Location: New Castle, Del. Injuries: 1 Fatal. Aircraft damage: Destroyed.
What reportedly happened: The pilot had logged 1,080 hours of flight time, with 425 hours in multiengine aircraft. Before arriving in the run-up area the pilot had lowered the airplane’s flaps, according to a witness. After the right flap fully extended, the flap key on the drive shaft inside the drive assembly adapter fractured. Before takeoff, the pilot attempted to raise the flaps. However, because of the fractured key, the right flap remained fully extended.
The pilot could have identified this condition prior to takeoff, either visually or by means of the flap indicator, which received its input from the right flap actuator. The pilot took off with asymmetrical flaps. The airplane turned left. The pilot climbed to 300 feet and allowed the airspeed to bleed off to where the airplane stalled and subsequently spun into the ground.
Airplane manufacturer calculations revealed that the pilot should have been able to maintain control at airspeeds over 70 knots. According to the pilot’s operating handbook, the best two-engine angle of climb airspeed was 99 knots and the best two-engine rate of climb airspeed was 120 knots.
Probable cause: The pilot’s failure to maintain adequate airspeed during a split flap takeoff, which resulted in an aerodynamic stall. Contributing to the accident were the failure of the right flap drive mechanism and the pilot’s failure to verify that both flaps were retracted prior to takeoff.
For more information: NTSB.gov