What happened
On May 20, 2013, an Eurocopter EC120B, registration F-HHFA, was performing a takeoff from a private helipad in Gassin, France. The flight was a training session involving an instructor, a student pilot, and two passengers, intended to proceed to Lyon Bron. The takeoff was conducted on a flat, grassy surface that had become soft due to recent rainfall.
As the student pilot, acting as the pilot flying, progressively increased the collective pitch, the helicopter began to move backward. During this maneuver, the rear of the right skid sank into the soft ground. The crew did not immediately notice this change in the aircraft's attitude. As the takeoff continued, the helicopter tilted heavily to the right. The instructor attempted to correct the movement by applying full left cyclic and reducing the collective pitch, but the rotor blades struck the ground, resulting in a dynamic rollover.
The investigation
The investigation focused on the physical state of the takeoff site and the flight crew's actions. Investigators found that the right skid had left a track in the grass approximately one meter long, reaching a depth of up to 10 cm. The aircraft's weight and center of gravity were within manufacturer limits, and there were no mechanical failures; engine and rotor RPM remained normal throughout the event.
Regarding the crew, the instructor had 756 total flight hours, while the student had 106 hours. The flight was categorized as a personal trip rather than a formal training flight, and no specific briefing had been conducted prior to departure. The weather conditions were favorable, with CAVOK visibility and a 10-knot wind.
Findings
- The primary cause was inappropriate takeoff technique, specifically a failure to monitor changes in aircraft attitude and a lack of anticipation regarding the helicopter's movement during the transition to a hover.
- The instructor's corrective reaction was delayed.
- The soft ground created an anchor point as the right skid sank, establishing a pivot point for the aircraft.
- The increase in power amplified the tilting motion, and because the vertical projection of the center of gravity moved outside the footprint of the skid, the reduction in collective pitch was insufficient to prevent the rollover.