ASH 25 Mi / B737-800 near miss — glider transponder inactive

An ASH 25 Mi glider and a Boeing 737-800 on IFR approach to Frankfurt-Hahn passed within 0.19 NM laterally and about 50 m vertically at roughly 2,000 m MSL; both aircraft continued safely. The glider was flying with engine off and transponder inactive. Its onboard TRX1090 alerted, the pilot visually acquired the airliner about 10 km out, and made a 45 degree left turn. The Boeing held course and its crew saw the glider only at the moment of passing. The inactive transponder left the glider invisible to TCAS and gave ATC nothing to relay as traffic, leaving see-and-avoid alone at high closure rate.

1. Cruise cross-country: The ASH 25 Mi motor glider was flying a VFR cross-country triangle from Marpingen with engine off, gliding at about 6,500 ft AMSL in Class E airspace east of Frankfurt-Hahn.
2. Collision warning: Around 17:30, at approximately 6,500 ft AMSL, the motor glider’s TRX1090 collision warning device generated a traffic alert indicating another aircraft at similar altitude nearby.
3. Transponder not active: Gliding with its engine off, the ASH 25 Mi was operated without its transponder active, so it did not appear on the Boeing's TCAS or as a correlated radar target for ATC.
4. High closure speed: The Boeing 737 was descending on an IFR arrival at about 250 kt while the motor glider glided at roughly 110 km/h, producing a very high closure rate and little time for visual avoidance.
5. Avoidance left turn: After sighting the airliner about 10 km away at similar altitude, the pilot immediately turned left onto a southerly reciprocal course, tracking roughly parallel to watch the Boeing's path.
6. Very close pass: Despite the avoidance turn, the aircraft passed with a minimum separation of about 0.19 NM horizontally and 161 ft vertically; the Boeing crew saw the glider only as it passed.
7. Safe landing: The motor glider resumed its southwest course, briefly crossing the Boeing's path 19 seconds later without wake turbulence, and later landed safely with no damage or injuries.