What happened
On August 27, 2016, a pilot and a passenger were flying a FK-Lightplanes FK12 Comet, identified as 974-GJ, from Blois – Le Breuil to the Houville-la-Branche ultralight airfield. During the arrival process, the pilot encountered significant atmospheric instability. While attempting the first approach to runway 26, the aircraft experienced a sharp right roll due to turbulence, forcing the pilot to abort the landing and climb.
Following advice from other pilots on the frequency, the pilot decided to divert to the nearby La Saussaye airfield. During subsequent approach attempts at Houville-la-Branche, the aircraft experienced further turbulence-induced rolls. On the final approach to runway 21, while attempting to correct the aircraft's position relative to the runway centerline, a final bout of turbulence caused a severe right roll. The pilot was unable to recover control, and the aircraft entered a steep dive, striking the roof of an uninhabited two-story barn. The impact resulted in two serious injuries and the destruction of the aircraft.
The investigation
The BEA examined the flight path using data extracted from the aircraft's GNSS calculator and the Dynon flight instrument system. The investigation analyzed the meteorological conditions, noting high temperatures and strong solar radiation, which were known to generate thermal turbulence. Investigators also reviewed the aircraft's flight history, noting that the pilot had experienced similar loss of control incidents during the two preceding approaches at the same airfield. The investigation also looked into the aircraft's handling characteristics, specifically whether the highly responsive nature of the FK12 made recovery difficult in such unstable air.
Findings
- The accident occurred during a period of high afternoon temperatures and intense sunlight, which created strong thermal updrafts and turbulent low-level air, as confirmed by ground witnesses.
- The pilot experienced three separate instances of loss of control during the arrival sequence due to turbulence.
- While the aircraft's airspeed remained above the stall speed during the incidents, the severe turbulence caused a roll that the pilot could not counteract during the final approach.
- The aircraft's high maneuverability and reactivity may have contributed to the difficulty in maintaining stability during the turbulent encounter.