What happened
On August 12, 2018, two gliders were conducting soaring operations near the Monte Vettore ridge in Italy. The first aircraft, a Discus b with registration D-8592, was flying with a south-facing heading, utilizing strong upward air currents along the mountain flank. The second aircraft, a Ventus 3F with registration D-KGCM, was flying parallel to the first, slightly faster and positioned behind it.
As the pilot of the D-8592 initiated a right-hand turn to exploit a spiral of rising air, the D-KGCM performed an abrupt pitch-up maneuver to avoid the collision. During this maneuver, the left wingtip of the D-8592 struck the fuselage of the D-KGCM, causing significant damage to the wingtip and the fuselage. Both pilots were able to maintain control of their respective aircraft and returned to Rieti airport safely.
The investigation
The ANSV conducted a desk investigation, analyzing flight data from the onboard FLARM (Flight Alarm) devices. The investigation reconstructed the flight paths, showing that the aircraft had convergent routes starting at 15:30 UTC. The data confirmed that the D-KGCM was trailing the D-85 592 at a higher speed before the contact occurred at approximately 15:33 UTC.
Investigators also examined the configuration of the electronic safety equipment. It was discovered that the FLARM system on the D-8592 had been incorrectly configured to "Balloon" mode rather than "Glider" mode. This setting altered the collision prediction algorithms and affected the data transmitted to other aircraft. Additionally, the pilot of the D-KGCM reported being distracted by persistent collision warnings on his own display, which he believed were also triggering in the other aircraft.