Introduction
On 26 July 2007 at approximately 15:17 UTC, a mid-air collision occurred 3.5 km north of Hodkovice nad Mohelkou airfield (LKHD) involving two gliders: an ASK 21 (registration D-2906) and an L 13 (registration OK-2813). The investigation was conducted by the Czech Accident Investigation Institute (ÚZPLN).
The Accident
According to a witness with aviation experience (an active Boeing 737 captain), several gliders were circling near Javorník hill. The ASK 21 left the group and flew toward LKHD, performing a half-roll to inverted flight. The L 13 also left the group and accelerated to catch up, positioning itself below the ASK 21 with a vertical separation of about 30 meters. Suddenly, the ASK 21 transitioned to a vertical dive, and approximately two seconds later, it struck the L 13. The left wing of the ASK 21 made contact with the fin of the L 13, indicated by yellow paint transfer. After the collision, both gliders descended; the ASK 21's student pilot did not escape and sustained fatal injuries on impact, while the instructor bailed out and suffered serious injuries. The L 13's pilot and passenger both bailed out and sustained minor injuries. Both gliders were destroyed.
The Gliders
The ASK 21 (serial number 21512, built 1991) had a total flight time of 1,360 hours. Its last annual inspection was on 26 April 2007. The L 13 (serial number 172111, built 1962) had a total flight time of 3,412 hours, with its last annual inspection on 15 April 2007. Both gliders had valid airworthiness certificates. The ASK 21 was not equipped with an additional pitot tube adapter recommended for aerobatic flight, which could cause an airspeed indication error of approximately 40 km/h when inverted.
Occupants
The ASK 21 carried a 39-year-old instructor with 824 total flying hours (82 on type) and a 14-year-old student with 16 hours 40 minutes total flying time (6 hours 45 minutes on type). Both held valid glider pilot licenses and medical certificates. The L 13 carried a 25-year-old pilot with 300 total flying hours (45 minutes on type) and a 25-year-old passenger with 400 total flying hours. Both also held valid licenses and medical certificates.
Investigation
The investigation revealed that the pilot of the L 13 had arranged a formation flight for photography with the ASK 21 instructor via radio. However, the ASK 21 instructor stated he did not intend to conduct photography and had set his radio volume low to give instructions to his student. He reported that while demonstrating inverted flight, he did not see the L 13 until about one second before the collision. The L 13 pilot stated he opened the airbrakes fully and pushed the control stick forward to avoid a collision. Medical examination confirmed that the ASK 21 student died on impact and did not attempt to escape the cockpit. The L 13's canopy was opened using normal locks, not the emergency jettison system. No flight recorders were installed on either glider. Weather conditions were not a factor.
Aftermath
Search and rescue were initiated by witnesses who called emergency services. The accident site was located on and around Buřín hill, with wreckage scattered in wooded and meadow areas. The investigation concluded that the collision resulted from the ASK 21's sudden dive while the L 13 was maneuvering below.