What happened
On September 7, 2014, at approximately 15:54 local time, a mid-air collision occurred near the Koblenz-Winningen airfield. A Roland Aircraft Z 602 XL ultralight aircraft was on final approach to runway 24, carrying a pilot and one passenger. Simultaneously, a Schleicher Ka 8 B glider was performing a training flight, having been launched via winch.
The glider pilot had initiated a left slip maneuver at an altitude of approximately 150 meters to increase the sink rate. During this maneuver, the glider's visibility to the left was significantly restricted. The ultralight pilot, while turning into the final approach, reported seeing a shadow from above before a heavy impact occurred. The two aircraft became interlocked at an angle of nearly 90 degrees, with the ultrallight's nose gear segment wedged into the glider's fuselage. Both aircraft were destroyed, and the three persons on board sustained minor injuries.
The investigation
The BFU investigation examined GPS data, radar records, and witness statements. The investigation focused on the communication between the pilots and the tower, the visibility conditions, and the accuracy of the airfield's aeronautical information. Investigators noted that while the weather was clear with good visibility, the sun was low on the horizon (approximately 23 degrees), which could have caused significant glare.
The BFU also reviewed the airfield's Aeronautical Information Publication (AIP), noting discrepancies between the documented glider circuit and the actual airspace used by pilots. Furthermore, the investigation looked into the radio performance of the involved aircraft and the ground station, as the pilots' accounts of received transmissions differed significantly.
Findings
Several factors contributed to the collision:
- Lack of mutual visibility due to the glider's slip maneuver and the ultralight's position relative to the horizon and sun glare.
- Inadequate communication between the pilots and the tower; the tower controller did not inform the ultralight pilot of active glider operations.
- Discrepancies in aeronautical documentation, specifically that the glider circuit depicted in the AIP was smaller than the area actually utilized by pilots.
- Radio communication issues, including potential deficiencies in the transmission or reception capabilities of the involved radios.
- The absence of a collision warning system on the ultralight aircraft, which could have alerted the pilot to the nearby glider.