What happened
On July 14, 2009, a Piel CP 605 B "Super Diamant," registration F-PNUN, was engaged in a cross-country flight from Nîmes-Courbessac to Etampes. The aircraft was occupied by the pilot and two passengers. After departing at 10:35 local time, the aircraft followed a trajectory passing south of Mende and climbing through various flight levels.
At approximately 11:55, while cruising at flight level 115, the aircraft began a series of maneuvers characterized by rapid descents. Radar data indicated the aircraft performed several turns while descending at rates of 1,000 feet per minute, eventually reaching a vertical speed of 7,000 feet per minute. The aircraft subsequently broke up in flight, with debris scattered over a three-kilometer area along a magnetic track of 220. The aircraft crashed near Nouhant, approximately 9 km northeast of the Montluçon-Guéret aerodrome, resulting in three fatalities and the total destruction of the aircraft.
The investigation
The investigation focused on the structural integrity of the airframe and the environmental conditions during the flight. Investigators examined the wreckage and found no evidence of manufacturing defects or structural weaknesses in the airframe. Instead, the evidence suggested that the structural failures were caused by excessive aerodynamic loads or abnormal stresses.
While the investigation could not definitively determine the cause of the accident, investigators noted that the canopy appeared to be unlocked at the time the high loads were applied, as it was found near its rear limit upon impact. It remained unclear whether the canopy opened due to the aerodynamic forces or if it had been opened intentionally by the pilot prior to the breakup.
Meteorological conditions at the site included visibility greater than 10 km, though some localized showers were possible. While high humidity was present, there was no significant meteorological instability along the flight path. The pilot had been in radio contact with Clermont-Ferrand information and had not expressed any concerns regarding the flight's progress.