What happened
On July 21, 2019, two gliders collided in the airspace near Lüneburg, Germany, while utilizing thermal updrafts. The first aircraft, an Alexander Schleicher ASW 15, had departed the Lüneburg landing field at 11:52 local time. The second aircraft, a Burkhart Grob Astir CS, departed shortly after at 12:06 local time. Both pilots were flying planned cross-country routes of approximately 45 and 450 km, respectively, but were not flying as a coordinated team.
At approximately 12:24 local time, at an altitude of 1,097 m AGL, the two aircraft collided. The pilot of the ASW 15 reported receiving a FLARM collision warning and seeing the other aircraft on his display, but he turned toward a cloud and subsequently perceived the collision. The impact caused the cockpit canopy of the ASW 15 to detach, sending the aircraft into a dive, though the pilot was able to recover and land the heavily damaged aircraft safely.
The pilot of the Astir CS experienced a severe loss of control following the impact. He attempted to egress the cockpit by deploying the canopy and releasing his harness. During his descent, his reserve parachute deployed but subsequently tore, leading to a high-velocity impact in a wheat field. The pilot sustained serious injuries, and the Astir CS was destroyed upon impacting a residential area.
The investigation
The BFU examined the flight path data from the ASW 15's FLARM system and GPS data from the Astir CS pilot's smartphone. The analysis revealed that in the 18 seconds preceding the collision, the two aircraft were flying on nearly intersecting courses. The investigation also included a technical examination of the wreckage and the reserve parachute. Forensic analysis by the LKA Niedersachsen confirmed that the red stains on the parachute were not foreign material from the aircraft, suggesting the canopy tore after deployment.
Findings
- The collision occurred because both gliders were flying on intersecting paths while climbing in straight-line flight.
- Both pilots failed to visually identify the other aircraft in time to take evasive action.
- Visual perception was significantly hindered by a "standing bearing" effect, where the aircraft were moving toward each other at nearly identical speeds, making relative motion difficult to detect.
- The low contrast between the white-painted gliders and the blue-white-grey sky further impeded visibility.
- Although both aircraft were equipped with FLARM collision warning systems and both pilots received alerts, neither pilot performed a situational analysis or adjusted their flight path following the warnings.