Ka 8 B and UL collide on simultaneous approaches to parallel runways

A Ka 8 B and a Z 602 XL ultralight collided on final to RWY 24 at Koblenz-Winningen; all three occupants were lightly injured and the wrecks fell into an orchard. Both approached the parallel asphalt and grass runways though the AIP forbade simultaneous approaches. The Ka 8 B, on a winch training flight, was higher than usual on downwind for side-slips, using only the brief local 'Position' call. As the glider entered a left slip at about 150 m, the UL — turning to final in a 30-45 degree bank — struck it from above-right and the wrecks interlocked at roughly 90 degrees. The Ka 8 B carried a collision-warning device; the UL did not.

1. Mixed circuit, motor + glider: Koblenz-Winningen (EDRK) has a 1,175 m asphalt runway (06/24) and immediately to the north a 1,175 m parallel glider grass strip used for winch and aerotow. Two motor circuits operate (north and south) plus a glider circuit. At about 15:54 LT on 7 September 2014 the south motor circuit to RWY 24 was active. The UL was inbound via the south motor circuit; the Ka 8 B had launched on the winch at 15:45 LT for a training flight in the glider circuit.
2. AIP forbids simul. approaches: Per the AIP, simultaneous approaches of aircraft to the asphalt and the parallel grass runway are not permitted because the lateral separation between the two strips is too small for independent operations. At the time of the accident both aircraft were nevertheless on approach to RWY 24.
3. Comms gap, no glider info to UL: When the UL pilot first contacted Koblenz Info about 12 minutes out the controller did not mention that glider operations were under way — a default that the BFU notes is necessary to prime arriving motor traffic for mixed-circuit operations. The Ka 8 B pilot made only the brief 'Position' call that is standard in the local glider circuit; that call is generally not enough under mixed operations to give arriving motor traffic a clear picture. The radio transmit and receive performance of one or more of the sets involved was also found to be deficient, and the radio traffic was not recorded.
4. Glider higher for side-slip practice: To create extra height for side-slip practice on final the glider pilot left the position higher than usual and extended the downwind to abeam the Koblenz-Güls sports field — the maximum extent normally flown for the local glider circuit but well beyond the glider circuit drawn in the AIP. From the UL's expected approach sector this meant the Ka 8 B was where an inbound motor pilot would not expect a glider.
5. Glider on left slip, UL on left turn: About two seconds after the Ka 8 B entered a left side-slip at about 150 m with full airbrakes, the Z 602 XL was turning onto final for RWY 24 in a 30-45° left bank. From the glider's cockpit the UL was below the horizon and partly obscured by the slip attitude; from the UL's cockpit the Ka 8 B was right and slightly above, but the UL pilot's attention was focused forward and toward the north circuit. Neither pilot saw the other before the strike.
6. UL strikes glider from above-right: The UL struck the Ka 8 B from above-right; the UL pilot reported seeing 'a shadow from above-right' an instant before a heavy impact. The glider pilot felt a dull bang then a louder second bang. The UL's upper nose-gear segment became wedged in the glider's fuselage tubing and the two aircraft were locked together at roughly 90°. The UL pilot deployed the Junkers Magnum SP rescue parachute but in his impression it did not fully open.
7. Interlock, fall to orchard: Interlocked, both aircraft descended and came to rest in an orchard about 600 m north-east of the airfield, at 460 ft AMSL — about 260 ft below the airfield level. Both aircraft were destroyed. The Ka 8 B pilot and the UL's pilot and passenger were lightly injured. The Ka 8 B was equipped with a collision-warning device; the Z 602 XL was not. The BFU concludes that had both aircraft been so equipped the collision would very likely not have occurred.