LS4-b / DG-300 mid-air — see-and-avoid failure, DG-300 FLARM non-functional

In a mid-air collision at about 1,100 m AGL near Borkenberge airfield, both pilots of a Rolladen-Schneider LS4-b and a Glaser-Dirks DG-300 were fatally injured. Neither pilot saw the other in shared thermal traffic. The DG-300's FLARM was non-functional due to a failed firmware update, contributing to the convergence going undetected. The LS4-b pilot bailed out but fell free of his parachute harness; the leg straps were not fully closed, which was linked to distraction while using an inflight urinal.

1. Cross-country thermaling: During cross-country soaring, the LS4-b was flying near Borkenberge and thermaling under cumulus clouds in an area with multiple other gliders.
2. Converging on same thermal: Both the LS4-b and the DG-300 independently approached and then flew in the same thermal area under a growing cumulus cloud, with the LS4-b slightly higher and overtaking the DG-300.
3. High traffic density: Several other gliders were operating in the vicinity of the cumulus cloud near Borkenberge, increasing collision risk in the thermaling area.
4. FLARM not operational: The DG-300’s FLARM option was not operating due to a failed firmware update, removing an intended layer of electronic collision warning.
5. Undetected convergence: While both gliders were flying on similar headings toward/within the same lift area, neither pilot detected the other in time to adjust separation despite vertical and lateral proximity.
6. Mid-air collision: At about 13:42:30 the LS4-b and DG-300 collided at approximately 1,100 m above ground, causing severe structural damage to both aircraft.
7. Crash - fatal: The DG-300 crashed to the ground with the pilot still strapped in, the LS4-b broke up with its pilot leaving the aircraft but not surviving, and both gliders were destroyed.