ASK 13 rope snags power line after releasing at the towplane

An instructor and student were seriously injured when their ASK 13 was dragged into a field at Montricher on take-off; aircraft substantially damaged. At about 20 m the towplane's hook opened by itself; the rope fell away but stayed on the glider's nose. Feeling the tow go slack, the instructor assumed the glider was off tow and focused on the railway line, not his own release. The trailing rope caught the line's earth wire and braked it hard into the field. The hook had latched only partially, an over-long wire fouling its release lever; the instructor also misread which side released, unprepared for an inadvertent release.

1. Aerotow takeoff: During an instructional aerotow departure from Montricher runway 03, the ASK 13 with instructor and student began the initial climb after a normal ground roll.
2. Tow hook wiring loop: On the towplane, the electrical lead to the tow-hook indicator was too long and formed a loop around the tow-hook release lever, preventing full closure of the hook latch.
3. Tow rope releases: At about 20 m above ground as the combination approached the tree line, the partially latched tow hook opened and the rope detached from the towplane while remaining attached to the glider.
4. Instructor misdiagnosis: The student did not report the rope had detached from the towplane; the instructor, feeling the loss of tow, assumed it had released from the glider and focused on clearing the railway line.
5. Rope snags power cable: With the rope still attached to the glider's nose, it brushed the treetops then wrapped around the railway line's earth wire, decelerating the glider and pitching it into a field.
6. Crash - serious injury: The glider crashed into a colza field about 60 m beyond the railway line, was heavily damaged, and both the student and instructor sustained serious spinal and leg injuries.