What happened
During a Part 135 proficiency check flight, the aircraft experienced a loss of control while performing a simulated engine failure maneuver. Witnesses near the site observed the aircraft traveling west at an altitude between 100 and 200 feet while in a descent. Observers reported hearing an engine surge and seeing the wings bank laterally. The aircraft subsequently struck power lines and a dirt field before flipping onto its back. Both pilots sustained serious injuries during the impact, and neither crew member could provide specific details regarding the flight sequence following the simulated engine failure.
Radar data analyzed by the NTSB revealed that the aircraft began a descent of 1,300 feet per minute approximately 1,100 feet above the ground. During a 30-second interval, the airspeed dropped from 130 knots to 92 knots. This descent rate remained steady for 45 seconds before accelerating to 2,000 feet per minute. Throughout the final 45 seconds of the flight, the true airspeed fluctuated between 88 and 102 knots.
Findings
An investigation of the aircraft surfaces revealed the presence of ice. A witness noted approximately 1/4 inch of clear and rime ice on the deice boots, while unprotected surfaces were covered in roughly 1/2 inch of ice. While the aircraft's stall speed in a clean configuration was 78 knots, the manufacturer's manual required higher approach speeds to account for ice accumulation. Specifically, the manual recommended an additional 10 to 20 knots of airspeed to compensate for increased weight and pre-stall buffet. For a flaps-up configuration, a minimum of 105 knots was advised, with even higher speeds required if 1/2 inch of clear ice was present. The aircraft's airspeed dropped below these recommended safety margins during the descent.