What happened
On Monday, June 19, 2000, at 13:20 local time, a Socata TB 10 aircraft, registration F-GDBM, experienced an engine failure while operating an instructional flight. The aircraft was en route from Saint-Pierre Pierrefonds to Saint-Denis Gillot over the Plaine des Cafres region of Réunion. While cruising at 6,500 feet, the engine stopped functioning.
The instructor in command took control of the aircraft and attempted to restart the engine, but the effort was unsuccessful. Although the propeller continued to windmill, the engine remained inoperative. Based on DME information from Saint-Denis, the instructor determined that a return to Saint-Pierre Pierrefonds via a glide was possible. During the descent, the instructor issued an emergency message on the Saint-Pierre tower frequency and monitored the availability of suitable emergency landing sites. The aircraft successfully landed on runway 15 at Saint-Pierre Pierrefonds and utilized its remaining momentum to clear the runway via the north taxiway.
The investigation
Following the incident, a mechanical inspection of the Lycoming O 360 engine was conducted. The investigation established that the upper mounting of the dual magneto (type D4 L.N 3000) had become completely detached, while the lower mounting was partially loosened. This misalignment caused the magneto's pinion to lose contact with the engine's drive pinion. Consequently, neither of the magneto's two circuits was able to deliver electrical energy to the spark plugs.
Records indicated that the torque of the mounting nuts had been inspected during a scheduled maintenance visit only 49 flight hours prior to the event.