France

The engine failure was the result of an incorrect refueling, due to an intake initial order probably incorrect that the incomplete application of procedures by the operator in charge of refueling and the lack of attention of the pilot did not allow recovery. The quantity of 100LL present in the feeders and the pipes allowed the taxiing and the take-off run, without the pilot noticing any anomaly. Once this quantity of 100LL consumed, the JET A1 present in the lower part of the tanks fed the engine and caused the power decrease.
Contributed to the accident:
- Coordination between the aerodrome operator and its subcontractors during the fuel order taken by the ramp agent, who does not encourage the operator in charge of refueling to confirm the type of fuel in a service carried out under strong time constraints,
- A usual practice for refueling certain types of helicopters, whose reservoir ports are not compatible with the dimensions of the standard refueling nozzles, which trivialize the change of nozzle for the refueling of JET A1, occasionally leading to the filling of order confirmation vouchers, thus reducing the effectiveness of the manifest safety for the operator through the presence of keying devices specific to each fuel,
- The ineffectiveness of the fuel type check item of the pre-flight procedure.

The collision with the ground was due to the deliberate and planned action of the copilot who decided to commit suicide while alone in the cockpit. The process for medical certification of pilots, in particular self-reporting in case of decrease in medical fitness between two periodic medical evaluations, did not succeed in preventing the copilot, who was experiencing mental disorder with psychotic symptoms, from exercising the privilege of his licence. The following factors may have contributed to the failure of this principle:
-The copilot’s probable fear of losing his ability to fly as a professional pilot if he had reported his decrease in medical fitness to an AME,
-The potential financial consequences generated by the lack of specific insurance covering the risks of loss of income in case of unfitness to fly,
- The lack of clear guidelines in German regulations on when a threat to public safety outweighs the requirements of medical confidentiality.
Security requirements led to cockpit doors designed to resist forcible intrusion by unauthorized persons. This made it impossible to enter the flight compartment before the aircraft impacted the terrain in the French Alps.

Due to the absence of any flight data recorder, investigations were unable to determine with certainty the exact cause and circumstances of the accident.

The accident was the consequence of the decision of the pilot to continue an unstabilized approach, resulting in a hard landing and the rupture of the left main gear upon touchdown.

During the flare the captain detected that the landing would be hard and in an emergency action, he quickly pulled the nose up without announcing his intention to the first officer who was the pilot flying. This lack of coordination within the flight crew caused a double controls and successive and opposite actions on the flight controls during the bouncing management.

Investigation did not reveal any technical element that could have contributed to the accident. However, considering the fact that the aircraft was totally destroyed upon impact, it was not possible to carry out all the examinations generally carried out on a wreck. It is possible the aircraft was flying in moderate icing conditions. Investigation could not determine if the deicing systems were activated. However, analysis of the flight path shows that the cruising speed was stable until the descent, which tends to indicate an absence of icing of the aircraft in normal cruise. A rapid and heavy icing of the aircraft during the descent making the aircraft to be difficult to control seems unlikely given the icing conditions predicted by Météo France. Investigations were unable to determine the reasons for the loss of control. Maybe it occurred during an unusual situation or any failure. Whatever the reasons, the lack of experience of the pilot on TBM-700, especially in the absence of visual references, may increase his workload beyond his capabilities, not allowing him to regain control of the aircraft. Once the loss of control occurred, given the weather conditions, it is very likely that the pilot did not recover any visual references until the collision with the ground.