Background
On the day of the accident, the pilot arrived at the aircraft at approximately 0900 to prepare for a flight to drop parachutists. The aircraft had been parked outside overnight and was covered in heavy frost. The pilot removed a cover from the windscreen and performed a pre-flight check, noting no ice or frost on the upper wing surfaces. He then returned to the operations building for pre-flight planning.
Preflight and Takeoff
The pilot started the engine at 1000. Weather conditions included a light north-west wind across grass Runway 06L, temperature -4°C, and QNH 1004 mb. While the engine warmed up, eight parachutists boarded: three instructors connected to three students, and two videographers (one the jump supervisor). After the engine warmed, the pilot performed a power check and before-takeoff checks, selecting flaps to TAKEOFF. All indications were normal. He taxied onto the runway and selected takeoff power (29 inches MAP, 2500 rpm). Acceleration seemed normal, but he rotated at 65 knots instead of the VR of 60 knots. Shortly after rotation, he selected flaps to FULL. The aircraft crossed the hedge at the runway end and began a left turn for noise abatement.
Accident
During the turn, the pilot noticed the aircraft descending. He checked engine instruments—MAP, fuel pressure, and rpm were normal. He called "BRACE, BRACE, BRACE," and the aircraft struck the ground in a left-wing-low attitude. It crossed a ditch, during which the landing gear detached, then skidded to a stop in the next field. The pilot exited through the left door but could not stand due to a leg injury. The rear left sliding door was jammed; parachutists exited via the pilot's door. One parachutist sustained a whiplash injury; the others were unhurt. The pilot was airlifted to hospital.
Investigation
Investigation revealed frost on the upper wing surface after the accident, suggesting it was present during takeoff. The windscreen, covered overnight, was clear both before and after the accident, indicating frost was not actively forming. Engine tests showed maximum power about 50 bhp below rated value, attributed to normal wear (engine ~75% through overhaul life). Calculated lift-off distance was 340–368 m, but actual distance was about 560 m, likely due to reduced engine power and rotation above VR. Takeoff performance may have been further reduced by frost, though the effect could not be quantified. During the turn, flaps were raised from FULL to TAKEOFF position (found post-accident), increasing stalling speed by approximately 3 knots on an uncontaminated wing. GPS recorded groundspeed of 58 knots six seconds before impact; with a light wind, IAS was slightly higher. The stalling speed with flaps in TAKEOFF on an uncontaminated wing was about 63 knots; frost could increase it to 75 knots. The frost on G-CDYA resembled medium sandpaper, compromising lift. It was deemed probable that the aircraft stalled in the turn due to frost on the wing, with a lower angle of attack at stall possibly preventing activation of the stall warning horn.