What happened
On September 4, 1999, at approximately 16:00, an Eurocopter SE 313 B (registration F-GFZQ) was performing a local flight at the Cosne-sur-Loire aerodrome. After completing an approach to the threshold of runway 12, the pilot maintained a hover in ground effect before attempting to transition toward the parking area by climbing along the runway.
During this maneuver, the pilot experienced a sudden loss of altitude. In an attempt to correct the descent, the pilot applied the collective pitch control. This input was excessive, causing the main rotor blade pitch to exceed the elastic limit (set at 14.5°). This sudden change triggered a turbine surge, resulting in a further loss of altitude. While the pilot managed to avoid striking the runway surface, the aircraft ultimately made a hard landing on the grass nearby.
The investigation
The investigation focused on the sequence of events leading to the loss of engine stability and the subsequent impact. Investigators examined the pilot's actions regarding the collective pitch control and the environmental conditions at the aerodrome. The investigation also looked into the presence of turbulence at the runway threshold. The chief pilot of the aeroclub confirmed that wind conditions from the east (10 to 15 knots) were creating downdrafts at the threshold of runway 12, likely caused by ground-level pressure changes and thermal effects.
Findings
- The primary cause of the incident was the inappropriate use of the collective pitch control to compensate for a loss of altitude.
- The excessive pitch input caused the turbine to experience a surge.
- The aircraft sustained significant damage to the turbine, landing gear struts, and skids.
- There were no injuries to the three occupants on board.