An investigation carried out by the National Transportation Safety Board initially determined that a malfunction of the flight control surfaces, including a rudder or ailerons hardover or asymmetric flaps, could not have caused the accident, after multiple pilots in simulators managed to keep the aircraft under control. Engine failure was also ruled out by detailed inspection of the two engines. The investigators found that the "circumstances of this accident indicate that a severe asymmetric thrust condition caused a left roll that led to loss of control of the airplane. The Safety Board's investigation examined all the possible events that could have caused the loss of control. The powerplant and propeller examinations indicated that the engines were operating normally but that a propeller system malfunction occurred" which allowed the left propeller's angles to be oriented nearly perpendicular to the direction of flight, resulting in insufficient thrust and higher drag on the left side.