A319 IFR avoids Ventus-2cM at FL 100; transponder off, TCAS blind

An Airbus A319 on IFR descent to Stuttgart (Germany) came close to a Ventus-2cM at FL 100, about 3,000 m MSL, near Heilbronn at the boundary between Class E and C; both aircraft landed safely. The A319 copilot saw the glider ahead at the same altitude, disengaged the autopilot, and turned left from heading 213 to about 200, while the Ventus pilot turned right. Minimum separation was about 0.9 km. The Ventus carried a transponder but it was off, ATC primary radar showed only an intermittent echo, and the A319's TCAS received no data. The captain stated that without the turn a collision would have occurred.

1. A319 IFR descent cleared to FL 100: Air traffic control cleared the A319, carrying 5 crew and 131 passengers, to descend to FL 100 at about 250 KCAS, a level marking the boundary between Class E and Class C airspace.
2. Ventus transponder OFF: The Ventus flew VFR, engine retracted, transponder off though mandatory above 5,000 ft AMSL; radar showed only an intermittent echo and the A319's TCAS received no data.
3. FL 100 = Class E/C boundary: In Class E, IFR traffic is separated only from other IFR traffic, not VFR traffic, so the controller could give only visual traffic information and no warning without a transponder return.
4. A319 copilot spots Ventus ahead: The A319 copilot spotted the glider on a similar heading directly ahead at the same altitude; the captain only acquired it visually after the avoidance turn was already underway.
5. A319 turns left 213° → ~200°: The copilot disengaged the autopilot and turned left from heading 213° to about 200° while holding FL 100 at roughly 250 KCAS; the controller approved the turn.
6. Ventus pilot turns right: The Ventus pilot also saw the airliner heading toward Stuttgart-Echterdingen and turned right, estimating the closest distance at 300-500 m; the A319 crew reported passing it on their right.
7. Min sep ~0.9 km; both land safely: The A319 crew estimated a minimum separation of about 0.5 NM (0.9 km); both landed unharmed, though the captain said a collision would have occurred without the avoidance turn.