What happened
On 21 March 2014, an AS355N Ecurel II, registration G-OLCP, was performing aerial work at Peterborough Conington Airport. The helicopter was preparing for a local survey flight and began hover-taxiing from its parking spot toward the runway. At the time, the weather was clear but windy, with surface winds recorded at 26 knots.
Nearby, a Cessna 152 was parked at the airfield's fuel installation. The aircraft had recently been refuelled and shut down, with a student pilot remaining inside the cabin while the instructor was temporarily away. As the helicopter moved, the pilot observed the tail of the Cessna lifting. The pilot immediately landed the helicopter on the grass to prevent further movement. However, the combination of the helicopter's rotor wash and the existing wind caused the tail of the Cessna to continue lifting until the aircraft ended up inverted. The student pilot, who was positioned with their upper body inside the cabin, managed to exit the aircraft and sustained one minor injury.
The investigation
The investigation examined the positioning of both aircraft and the environmental conditions. It was noted that the Cessna 152 had been parked in a position that was largely downwind. The investigation also considered the movement of the helicopter; although the helicopter was moving away from the Cessna, its path took it upwind of the parked light aircraft. The investigation looked into the impact of rotor turbulence, noting that the helicopter's rotor diameter was 10.69 m.
Findings
- The primary cause of the incident was the interaction between the helicopter's rotor wash and the strong surface wind, which acted upon the parked Cessna 152.
- The Cessna 152 was positioned in a manner that made it susceptible to the wind and turbulence.
- The helicopter's movement caused it to pass upwind of the stationary aircraft, increasing the effect of the rotor wash on the light plane.