The DC-3 departed Tehran at 09:09 for an instrument check flight, also practicing one engine flying. Feathering and unfeathering problems forced the crew to return to the airport. The DC-3 took off again at 10:48. At 11:29 the aircraft was flying at 6700 feet when the no. 1 propeller was feathered. When the prop oversped, the check pilot tried to unfeather it unsuccessfully. The prop continued to windmill at 2100 rpm. A crash-landing was made 1500 m short of Tehran runway 11. PROBABLE CAUSE: “With the left propeller windmilling, the right propeller did not develop sufficient thrust to enable an emergency landing to be carried out on runway 11 at Mehrabad Airport. The Committee has concluded that this was caused by mishandling of the controls by one or more of the flight crew members since the Committee has not found any evidence of malfunctioning of the right engine or of its propeller.”