ASK 21 rear canopy fails in turbulence — student outlands safely in maize field

An ASK 21 outlanded safely in a young maize field near Locarno (LSZL, Switzerland) on a solo student aerotow; there were no injuries. In turbulence after the Ticino river a pre-existing fracture in the rear canopy's steel tube mounting failed with a loud bang, the canopy frame deformed, and the plexiglass shed in flight. The glider began to sink rapidly and the student released at about 425 m AMSL. The sink rate ruled out a return to Locarno, so the student picked a nearby field, radioed the tower, and landed. The pre-existing mount damage in strengthening northerly wind was identified as the trigger.

1. Solo student aerotow from Locarno: ASK 21 aerotowed at 11:17 from Locarno (LSZL) RW 08R; pilot (b. 1971, 15:27 h total, 5:11 h on type) solo for 2nd flight of the day. Rear canopy verified closed by instructor pre-flight.
2. Pre-existing damage to canopy mount: The rear canopy's right steel-tube support had corrosion-related weakening; the gas-strut bearing hole was elongated. Both not easily visible at routine inspection.
3. Strengthening N wind, turbulence: After crossing the Ticino river the tow encountered stronger turbulence, briefly losing height then climbing rapidly.
4. Rear canopy fails in flight: Loud bang from behind, sudden drag increase. Under load the right steel tube fractured at a weak point; the gas strut (elongated bearing) pushed in the wrong direction; the canopy shifted and the front locking bolts pulled out.
5. Student releases tow: Glider began rapid sink; student released the tow at ~425 m AMSL (~225 m AGL) and turned right toward Locarno.
6. Outlanding committed: Recognizing the sink rate would not allow a return, the student picked a nearby field and radioed Locarno tower.
7. Safe outlanding in maize field: Landed in a young maize field 4 min after release; no injuries; damage limited to the rear canopy frame and plexiglass.