Lyon-Bron

It was determined that both engines stopped due to fuel exhaustion. Investigations reported that the crew failed to prepare the flight according to published procedures and no fuel was added in the tanks prior to departure from Lyon-Bron Airport. During the stop at Tours Airport, the crew failed to check the fuel quantities and no additional fuel was added.

According to the investigating committee, the accident was the direct result of a collision with the terrain, which occurred at night in stormy conditions in the vicinity of a cold front, while the aircraft was following a seemingly normal approach procedure but deviated to the east about 30 km. The genesis of the accident has two anomalies. The first consists in the fact that the crew was convinced to be really vertical of Clermont-Ferrand whereas this beacon was, in fact, more than 30 km away. It can only be explained by a frank rotation of the radiocompass whose crew did not detect the aberrant character. It must also be admitted, moreover, that the radiocompass indications subsequently showed consistent variations with the successive positions of the aircraft during the double descent circuit and with the second overflight of the Clermont-Ferrand beacon. The second anomaly is characterized by the announcement of the aircraft flying over the beacon, with more than three minutes ahead of an estimated eight minutes. This difference may have been neglected by the crew because of their reliance on the radiocompass indication. We can also think that this difference went unnoticed by the crew either by forgetting to check the time, or by a reading error, the crew having to cope with a difficult steering because of the turbulence and the presence of an instructor who could also be a factor of concern and distraction at this time. The commission's work has made it possible to rule out the assumption of a pirate transmitter, the erroneous indication of the radiocompass could have come from either a fault in the installation of the on-board antenna system associated with certain conditions of the electric field , or more likely very localized precipitation that accompanied the cold front in the area of ​​the accident and that could constitute a kind of transmitter (series of micro discharges) powerful enough to be during all this phase of flight detected by the radiocompass of the plane while stifling the field of the beacon of Clermont-Ferrand. The interception of the ILS alignment plan probably reinforced the crew's conviction. In addition, it is not impossible that the luminous halo of the city of Thiers, perhaps visible at certain times, could constitute an additional factor of motivation. Although the instructor pilot had the reputation of attaching great importance to a cross-checking of positions, which was possible in particular by the radial of Moulins, it seems that the crew did not do anything about it. The commission ultimately accepts the possibility of an aberrant indication of a radiocompass, but can not explain the reasons which prevented the crew from properly controlling the point from which the descent was started and continued. In conclusion, it is understood that the accident was the consequence of a controlled flight into terrain.

The Board considered:
- that the aircraft would probably have landed safely if it had been able to carry through the approach it had initiated;
- that the accident resulted from the exceptionally bad weather conditions in the area where the aircraft was holding at the request of Lyon Approach.
The Board did not rule out the possibility of a flash of lightning dazzling the crew and causing temporary blindness or appreciably incapacitating both crew members.

The failure of the starboard engine was the consequence of the breaking of a seal in the hydraulic propeller pitch control system. The breakage caused periodic variation of the pitch and hence variations in the speed of the engine. The vibrations of the port engine according to the statement of the crew and experts, were undoubtedly due to an ignition defect. The ignition harness was found to be below requirements.

It is believed that the pilot-in-command lost his visual references on final approach due to foggy conditions and did not realize his altitude was too low.

It was determined that the crew failed to prepare the flight properly and according to procedures. For unknown reason, the altitude mentioned on the flight plan was 8,200 feet, which is insufficient to pass over the Alps. A gap of 13 degrees was also noted on the heading (flight path), maybe due to the fact that the crew mistook the Poretta and Bastia beacons, close to each other. Also, it was noted that a wind was blowing at 45 knots from the southwest, which probably contributed to deviate the aircraft from the prescribed flight path.