Flight and Witness Observations
The accident flight departed with a pilot, co-pilot, and eight passengers. Multiple witnesses on the ramp reported that the airplane sounded underpowered immediately after takeoff, with one describing it as “like it was at a reduced power setting.” Another witness stated the airplane seemed not to have sufficient power for takeoff. A third witness characterized the rotation as “steep,” and others thought the airplane was performing aerobatics. Digital video from multiple cameras showed the airplane roll left, reach a maximum altitude of about 100 ft above ground level, then descend and impact an airport hangar in an inverted attitude approximately 17 seconds after takeoff. An explosion occurred immediately, and after breaching a closed roll-up garage door, the airplane came to rest on its right side outside the hangar and was engulfed in a postimpact fire.
Cockpit Voice Recorder and Performance Data
Sound spectrum analysis of the cockpit voice recorder (CVR) estimated propeller speeds at takeoff power (1,714 to 1,728 rpm) at liftoff. About 7 seconds later, propeller speeds diverged: left propeller decreased to about 1,688 rpm and right to 1,707 rpm. Based on the airplane’s estimated calibrated airspeed of about 110 knots and the rpm at divergence, estimated thrust in the left engine decreased to near zero while the right engine continued at slightly less than maximum takeoff power. Analysis estimated that 2 seconds after the propeller speed deviation, the airplane’s sideslip angle was nearly 20°. During the first 5 seconds after deviation, roll rate was about 5° per second to the left, then rapidly increased to more than 60° per second before the airplane rolled inverted.
Wreckage Examination
Examination of the wreckage found both main landing gear extended and the left propeller unfeathered. The condition of the wreckage precluded determining whether the autofeather system was armed or activated. Witness marks on the left engine and propeller, the reduction in propeller speed, and the airplane’s left roll suggest a loss of thrust in the left engine shortly after takeoff. Engine and propeller examinations and functional evaluations of controls found no condition that would have prevented normal operation; evidence of operation in both engines at impact was found.
Pilot Actions and Response
The airplane manufacturer’s engine-out procedure during takeoff instructs: retract landing gear once a positive rate of climb is established, feather the propeller of the inoperative engine, and apply right rudder to balance yaw. The pilot did not retract the landing gear or feather the left propeller. Calculations based on sideslip angle shortly after propeller speed deviation determined that the thrust asymmetry alone was insufficient to produce the sideslip angle. Evaluation of thrust estimates and performance data indicated that the pilot likely applied left rudder (the opposite input needed) before applying right rudder seconds later. By then, the roll rate was increasing too rapidly and altitude too low to recover. Data supported that directional and lateral control could have been maintained if right rudder had been commanded initially.
Investigation Findings
The pilot’s confused reaction to the airplane’s performance suggests he may have been startled by a stall warning that followed the propeller speed divergence, possibly prompting the initial improper rudder input. The NTSB investigation estimated rotation occurred before Vr (rotation speed), decreasing the margin to minimum controllable airspeed and likely reducing time available to react. Although the airplane was slightly over maximum takeoff weight, the rate of climb was near expected at that weight in the prevailing weather conditions, so weight exceedance likely was not a factor. The CVR lacked callouts for checklists, and the pilot had a reported history of not using checklists. It is possible the pilot did not check or adjust the power lever friction locks before the flight, leading to uncommanded throttle movement, but heavy fire and impact damage precluded determining throttle position or friction setting. Thus, the reason for the thrust reduction could not be definitively determined. The co-pilot, who was not type-rated and not allowed to operate flight controls with passengers on board, verbally identified the left engine loss but likely did not initiate corrective inputs.