What happened
On July 6, 2014, at approximately 16:16 local time, a winch-assisted glider launch was underway at Schänis airfield (LSZX). A Robin DR 400/180 R, registration HB-EXU, was performing a private VFR glider tow operation. Shortly after departing from runway 34, the cockpit canopy of the glider unexpectedly opened.
During the climb, the glider pilot noted a change in flight attitude, specifically a nose-down pitch, which required corrective elevator input to maintain the intended climb speed. Following the canopy opening, the glider pilot either released the tow cable or the cable snapped. The glider pilot, having sufficient altitude to reach runway 16, opted to release the cable and proceed with a landing on that runway, which was completed without further incident.
Simultaneously, the tow aircraft, a Duo Discus glider with registration HB-3416, continued its climb. After the loss of the tow, the electric winch was used to retract the cable. Due to remaining knots in the cable, the tow pilot performed a steep approach to runway 34 to avoid ground obstacles, landing safely.
The investigation
The investigation focused on the circumstances leading to the sudden opening of the HB-EXU canopy and the subsequent loss of the tow. Investigators examined the flight sequences of both the Robin DR 400/180 R and the HB-3416.
Findings
- The cockpit canopy of the Robin DR 400/180 R opened for unknown reasons despite a pre-flight inspection being performed.
- It is possible that the passenger may have inadvertently manipulated the locking mechanism while attempting to steady themselves during turbulence.
- The loss of the tow was caused by the unintentional release of the canopy, which led to the pilot either manually releasing the cable or the cable breaking.
- The passenger in the glider sustained serious injuries during the event.