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 AMSL; 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: Because the ASH 25 Mi was gliding with its engine off, it was operated as a sailplane without its transponder activated, 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 knots while the motor glider was in slow glide at roughly 110 km/h, creating a very high closure rate and little time for visual detection and avoidance.
5. Avoidance left turn: After visually acquiring the airliner about 10 km away at similar altitude, the motor glider pilot immediately initiated a left turn to a southerly reciprocal course and remained on a roughly parallel opposite track to monitor the Boeing’s path.
6. Very close pass: Despite the avoidance maneuver, the aircraft passed each other on nearly opposite parallel tracks with a minimum separation of about 0.19 NM horizontally and 161 ft vertically, with the Boeing maintaining course and altitude and its crew only sighting the glider at the moment of passing.
7. Safe landing: The motor glider then resumed its original southwest course, briefly crossing the Boeing’s flight path about 19 seconds and roughly 300 ft below its previous altitude without encountering wake turbulence, and later landed safely with no damage or injuries.