What aircraft was involved and where did it happen?

The accident on 2010-04-18 involved a 1) Grob G 103 C „Twin III“, at Utscheid, DE.

What was the probable cause of the accident?

The collision occurred because the pilots failed to maintain visual separation after changing their flight paths, and the automated collision warnings from the FLARM systems were ignored.

Mid-air collision between two gliders near Utscheid

A collision between a Grob G 103 C and an Alexander Schleicher ASK 18 resulted in the destruction of one aircraft and minor injuries to three people.

What happened

On April 18, 2010, two gliders were participating in thermalling maneuvers near the Utscheid glider airfield in Germany. The first aircraft, a Grob G 103 C "Twin III", departed at 17:23 for a pleasure flight with a passenger. Shortly after, at 17:31, an Alexander Schleicher ASK 18 departed for a local training flight.

Both aircraft were flying in circles within the same thermal updraft. As the flight paths shifted, the center of the circling pattern moved, causing the Grob G 103 C "Twin III" to approach the ASK 18 from behind. At approximately 17:49, at an altitude of roughly 1,200 meters above ground level, the two aircraft collided. The left wing of the Grob G 103 C "Twin III" struck the cockpit canopy of the ASK 18, causing significant structural damage to the latter's cockpit area and breaking off a 3-meter section of the Grob G 103 C "Twin III" wing.

Following the impact, the pilot of the Grob G 103 C "Twin III" entered a steep spiral with rapidly increasing speed. Both the pilot and the passenger were forced to exit the aircraft using emergency parachutes. The student pilot in the ASK 18 also exited through the damaged canopy. All three persons involved sustained slight injuries upon landing.

The investigation

The BFU investigation utilized GPS data from FLARM loggers installed in both aircraft to reconstruct the flight paths. The analysis revealed that while the aircraft initially flew in separate updrafts, the ASK 18 entered the same thermal as the Grob G 103 C "Twin III" at approximately 17:44. The investigation confirmed that the Grob G 103 C "Twin III" approached from the rear right and that the ASK 18 pilot could not see the approaching aircraft.

Technical inspections of both aircraft showed no mechanical failures or maintenance issues. Both aircraft were properly registered and airworthy, with weight and balance within limits. The investigation also noted that while both aircraft were equipped with radio and FLARM collision warning systems, there was no radio communication between the two pilots during the incident.

Findings

The primary cause of the accident was that both pilots lost visual contact with each other following a shift in the circling flight path.
The ASK 18 was not identified in time to allow for an effective evasive maneuver.
The Grob G 103 C "Twin III" was positioned in the blind spot of the student pilot in the ASK 18.
The optical and acoustic warnings provided by the FLARM anti-collision devices were not acted upon or observed.