Falcon 2000 passes glider with 500 m separation, same altitude

A Dassault Falcon 2000 on an IFR flight from Munich to Paderborn-Lippstadt (Germany) passed an unidentified glider at the same altitude near Paderborn-Lippstadt with an estimated 500 m lateral separation; the Falcon landed safely. The Falcon had been cleared down to 1,525 m AMSL on Langen Radar when both pilots first sighted the glider on an opposite heading at roughly 1,000 m. The glider had no transponder and did not appear on civilian or military radar. A second glider encounter occurred later on the same flight at about 1.3 NM and 30 m vertical; that glider was transponder-equipped and the controller issued traffic info.

1. IFR descent toward Paderborn-Lippstadt: On 18 April 2015 a Dassault Falcon 2000 of a German operator was on an IFR flight from Munich to Paderborn-Lippstadt with two crew and four passengers. After step-down clearances on Langen Radar (passing FL93 at 14:27:28 LT, then cleared to FL70, then to 5,000 ft AMSL at 14:28:18 LT), the Falcon was descending in Class E airspace. METAR Paderborn-Lippstadt reported CAVOK with surface visibility 10 km or more.
2. Glider VFR without transponder: An unidentified glider was operating VFR in the same airspace without an active transponder. It therefore did not appear continuously on civilian ATC or military radar, no traffic information could be issued, and ACAS on the Falcon could not detect it. Above 5,000 ft AMSL transponders are required for powered aircraft but gliders are exempt.
3. Glider on opposite heading at 1,000 m: At about 14:31 LT both Falcon pilots first sighted a glider suddenly appearing in front of them on an opposite heading at the same altitude (5,000 ft AMSL / ~1,525 m). They estimated the first sighting distance at roughly 1,000 m.
4. Pass at ~500 m, same altitude: The glider passed the Falcon 2000 at the same altitude with an estimated lateral separation of about 500 m — a serious loss of separation in Class E airspace.
5. Lands PAD; 2nd glider met later same flight: The Falcon continued and landed at Paderborn-Lippstadt with no injuries and no damage. Later on the same flight the crew encountered a second glider; this glider was transponder-equipped, the controller issued traffic information and an avoidance recommendation, the closest separation was about 1.3 NM horizontally and 100 ft (~30 m) vertically, and the BFU did not classify this second encounter as a serious incident. The first glider could not be identified.