What happened
On July 24, 2018, a Robinson R44 helicopter, registration F-GLYF, was performing a local flight near Houdainville, France. The flight began at the Plessis Belleville aerodrome, with the pilot and a passenger—the aircraft's previous owner—heading toward the Sansonnière pond. After an initial flight, the crew configuration changed to include two additional passengers for a second flight.
During the takeoff from the pond, the pilot attempted to transition from a hover to forward flight by moving laterally over the water and then accelerating along the shoreline to find a clear path away from nearby trees. As the aircraft accelerated, the pilot experienced a lack of sufficient power to maintain altitude or increase airspeed. Realizing a collision with the water was imminent, the pilot chose to avoid a violent pitch forward by attempting a controlled landing on the water. The helicopter struck the surface with its skids and cabin, subsequently capsizing and sinking to a depth of six meters. All four persons on board successfully evacuated the submerged aircraft through the right-side doors.
The investigation
The BEA investigation focused on the aircraft's performance and the environmental conditions at the time of the accident. Investigators examined the wreckage after it was recovered from the pond floor. The examination of the transmission system, including the gearbox, pulleys, and driveshaft, confirmed that the engine was functional and providing power at the moment the rotor blades struck the water. The damage to the airframe was determined to be a direct result of the extreme forces applied when the rotor hit the water.
Investigators also reviewed the pilot's experience and the flight planning. The pilot, who had 1,130 total flight hours, was returning to flight after a nine-month hiatus and was not highly experienced in operating in confined areas or over water. The investigation also noted that the passenger in the front seat had provided safety briefings regarding seatbelts and door operation, which proved critical during the underwater evacuation.
Findings
- The accident was caused by an insufficient consideration of the helicopter's performance limitations.
- The pilot was operating in a confined environment with nearby obstacles (trees).
- High ambient temperatures (32°C) and the transition from ground effect to out-of-ground-effect flight reduced available power.
- Flying at a low altitude over a water surface made it difficult to accurately judge height and aircraft attitude due to a lack of external visual references and reflections from the trees on the water.
- The takeoff maneuver involved a nearly constant turn, further complicating the power management.