What happened
On June 4, 2004, an MD 600 N helicopter, registration D-HJER, was conducting a flight instruction mission at low altitude. The flight, which included an instructor, a student pilot, and one passenger, was traveling at a cruise speed of approximately 140 knots at an altitude of 800 feet.
During the flight, the instructor initiated an unannounced simulation of an engine failure. This sudden reduction in power, combined with the aircraft's high cruise speed, prompted an abrupt control response from the student pilot. This maneuver caused the main rotor blades to flex significantly, leading to a catastrophic interaction where the blades struck the composite tail boom. The tail boom separated from the fuselage in mid-air, causing the helicopter to lose stability and impact the ground in a field near Saint-Salily-de-la-Balme. The impact resulted in two fatalities among the crew.
The investigation
The BEA investigation focused on the mechanical integrity of the airframe and the sequence of pilot inputs. Investigators examined the wreckage, noting that the tail boom had separated approximately 2.45 meters from its attachment point. Analysis of the main rotor blades revealed deep gouges and deposits from the tail boom, confirming that at least four of the six blades had struck the structure.
Engine monitoring data from the FADEC system showed no mechanical anomalies or engine malfunctions prior to the accident. The investigation also looked into the maintenance history, finding that the aircraft had been recently maintained and that a previous repair to the tail boom was structurally sound and did not contribute to the failure. Furthermore, investigators examined the tachymeter, which was known to have a display error, to determine if instrument uncertainty played a role in the crew's response.