What happened
On December 11, 2007, at 11:55 local time, a Coupé JC 483 G aircraft, registration F-PNLY, was performing a ferry flight from Alençon to Le Touquet. The aircraft, a tailwheel-type amateur-built plane, was taxiing on the paved runway at Alençon aerodrome. At the same time, an EC 135 helicopter was conducting instructor qualification exercises on the adjacent unpaved runway 07.
As the pilot of the F-PNLY proceeded toward the threshold of runway 07, the helicopter pilot moved to a position approximately 25 to 30 meters away from the paved runway and entered a hover. As the aircraft passed the helicopter, the aircraft tipped forward. The propeller struck the ground, causing the aircraft to come to a rest on its nose.
The investigation
The investigation examined the movements of both aircraft and the environmental factors at the aerodrome. The pilot of the F-PNLY confirmed awareness of the helicopter's presence and had heard the helicopter pilot's radio intentions. The pilot chose to taxi on the paved runway because the unpaved taxiway parallel to the runways is difficult to use for aircraft with a conventional landing gear configuration.
The helicopter pilot reported moving to the left to increase the distance from the paved runway. However, the investigation noted that the aerodrome's visual charts did not contain specific restrictions regarding the simultaneous use of the paved and unpaved runways, other than noting the unpaved strip was reserved for gliders and service aircraft.
Findings
- The primary cause of the accident was the insufficient consideration of the main rotor downwash effects from the EC 135 helicopter.
- Recent studies indicate that the downwash from an EC 135 can pose a hazard to objects and persons at distances of up to 30 meters while the helicopter is hovering in ground effect.
- The aircraft sustained propeller damage as a result of the nose-over.