What happened
On June 12, 2011, at 15:57 local time, a mid-air collision occurred near Lake Renkajärvi in Hattula, Finland. Two single-seat sailplanes, registered as OH-920 (competition ID YX) and OH-983 (competition ID BO), were participating in the Finnish Gliding Championships. The accident took place at an altitude of approximately 1,400 meters within the Pirkkala Military Control Area (Class D airspace) under favorable weather conditions.
Prior to the impact, both aircraft were flying nearly the same route and were occasionally in very close proximity. The collision occurred when the lower-flying aircraft, the Ventus 2a (OH-920), increased its altitude while reducing speed, striking the underside of the higher-flying ASW 27-18E (OH-983).
The force of the impact caused the rear fuselage and right wing of the Ventus 2a to break off, and the canopy shattered. The aircraft entered a steep dive, during which the left wing also detached, causing the fuselage to strike the ground at high speed. The pilot of the Ventus 2a was found outside the wreckage; although the seatbelt had been unfastened, the parachute had not been deployed. The pilot was killed. The pilot of the ASW 27-18E sustained minor injuries after deploying a parachute and landing in a tree.
The investigation
The investigation examined GPS data from both aircraft, which recorded flight paths at four-second intervals. Investigators also analyzed the functionality of the FLARM collision avoidance systems installed in both aircraft. The investigation established that while both pilots were experienced competitors, the aircraft were flying on intersecting flight paths in the vertical plane.
Findings
Insufficient situational awareness by the pilots caused the aircraft to drift into a position where their flight paths intersected vertically, making it impossible for the pilots to see one another. A contributing factor was that the FLARM collision avoidance system failed to provide an alert prior to the collision. The investigation noted that the lack of warning was due to the inherent technical limitations of the FLARG system as described in its manual.
Safety action
The Finnish Safety Investigation Authority issued a safety recommendation to the Finnish Aeronautical Association, suggesting that safety briefings and information sessions be held before every gliding competition and at the start of each competition day.