Circumstances
Witnesses reported that the airplane's takeoff ground roll appeared normal. Shortly after lifting off, the airplane stopped climbing and yawed left. Several witnesses heard abnormal sounds, which they attributed to propeller blade angle changes. The airplane's flight path deteriorated into a left skid, and its airspeed began to decrease. The left bank angle increased to between 45 and 90 degrees, and the nose dropped to a nearly vertical attitude. Just before impact, the bank angle and pitch began to flatten. The airplane had turned left about 100 degrees when it struck the ground approximately 1,500 feet from the midpoint of the 10,000-foot runway. A fire erupted and consumed the fuselage.
Video and Witness Accounts
Review of a security camera video revealed that the airplane was near the midpoint of the runway, about 140 feet above ground, at a ground speed of about 130 knots when it began to yaw left. The left yaw coincided with the appearance of a dark grayish area behind the airplane, which appeared to be smoke. A witness, an aviation mechanic with extensive experience on the same make and model, reported hearing two loud "pops" around the time the smoke appeared, which he believed were generated by one of the engines intermittently relighting and extinguishing.
Postaccident Examination
Postaccident examination of the airframe, engines, and propellers revealed no anomalies that would have precluded normal operation. Both engines and propellers sustained nearly symmetrical damage, indicating that both engines were operating at similar low- to mid-range power settings at impact. The left and right nacelle fuel tanks were breached, and no fuel was found in either tank. Samples from the fuel truck tested negative for contamination.
Fuel System and Contamination
The airplane's fuel system comprised two separate systems (one per engine), with multiple wing tanks feeding into a nacelle tank and then to the engine. A fuels research engineer from the United States Air Force Fuels Engineering Research Laboratory stated that water contamination can result from condensation in the air cavity above a partially full fuel tank, influenced by diurnal temperature and atmospheric pressure variations. He noted that draining the fuel tank sumps before every flight is the simplest preventive action. The Pilot's Operating Handbook (POH) required draining six fuel drains on each wing before every flight. The investigation revealed that the pilot's previous employer, where he gained most of his experience in the same model, did not require pilots to drain sumps before each flight; maintenance personnel drained them at an unknown interval. No witnesses observed the pilot conducting a preflight inspection before the accident flight, and it could not be determined whether he drained the sumps. He had been the only pilot of the airplane for its previous 40 flights. Because the airplane was not on a Part 135 certificate or continuous maintenance program, it was unlikely a mechanic routinely drained the sumps.
Pilot Experience and Weight
About five months before the accident, the pilot successfully completed a 14 Code of Federal Regulations Part 135 pilot-in-command check flight in a King Air 90. No documentation was found indicating he had received training in a full-motion King Air simulator, although such training was not required. When the left yaw began, the airplane's airspeed was more than 40 knots above the minimum control speed of 86 knots. The estimated weight at the time of the accident was about 650 pounds over the maximum allowable gross takeoff weight of 12,500 pounds, but the investigation determined this additional weight would not have precluded directional control.
Probable Cause
The official probable cause is: The pilot’s failure to maintain directional control of the airplane during a momentary interruption of power from the left engine during the initial takeoff climb. Contributing to the accident was the power interruption due to water contamination of the fuel, which was likely not drained from the fuel tanks by the pilot during preflight inspection as required in the POH.