What happened
On July 5, 2017, a Schweizer 269C helicopter, registration F-GHAF, was conducting a flight training session near La Ferté-Alais, France. The flight was a proficiency check for a student pilot, accompanied by an instructor. During the flight, while over wheat fields, the instructor initiated an engine failure simulation exercise.
As the student pilot attempted to transition into autorotation by reducing the engine to idle, the engine unexpectedly stopped. The instructor took control of the aircraft while the student attempted to restart the engine, but these efforts were unsuccessful. To avoid the risk of fire in the nearby wheat crops, the instructor decided to land on an adjacent farm track. During the landing flare and subsequent slide, the right skid struck a mound of earth hidden by vegetation, causing the helicopter to overturn on its right side. There were no fatalities and no injuries reported.
The investigation
The BEA examined the aircraft's engine, the flight site, and the pilots' procedures. Testing of the Lycoming HIO-360-D1A engine on a test bench showed it was capable of delivering expected power, and the investigators could not definitively replicate the in-flight shutdown. However, the investigation identified that the right magneto showed significant wear and the spark plug electrode gap was outside acceptable tolerances. Additionally, the starter was found to be heavily aged and unable to restart the engine when hot.
The investigators also reviewed the flight manuals. The crew was using a 1975 French-language version of the manual, which lacked modern warnings. A more recent English-language version contained specific warnings against rapid throttle reductions to idle and instructions to perform a vertical landing rather than a sliding landing if the landing area had not been meticulously inspected.
Findings
- The engine shutdown may have been caused by a combination of high ambient temperature (31°C) and a degraded magneto, or potentially triggered by the rapid throttle reduction during the simulation.
- The failure to restart the engine in flight was due to a worn starter that could no longer function effectively under hot conditions.
- The helicopter overturned because the pilot did not ensure the landing surface was suitable for a sliding landing, leading to the right skid striking a hidden obstacle.
- The use of an outdated flight manual meant the crew was unaware of modern safety warnings regarding throttle management and landing techniques.