Incident Overview
On 6 July 2014 at 16:16 local time, a Robin DR 400/180 R, registration HB-EXU, was towing a Duo Discus glider, registration HB-3416, at Schänis airfield (LSZX) for a private VFR glider tow flight. Shortly after takeoff from runway 34, the canopy of the glider opened unexpectedly, leading to a series of actions by both pilots.
Sequence of Events
According to the glider pilot, despite a pre-takeoff check, the canopy over the cockpit opened for unknown reasons shortly after starting the takeoff. The pilot speculated that the passenger may have held onto the locking mechanism due to turbulence, inadvertently opening it. While attempting to close the canopy, the pilot lost sight of the towplane. Judging that altitude was sufficient for a landing on runway 16, the glider pilot decided to release the tow rope and performed an uneventful landing.
The tow pilot reported that after takeoff, he noticed a change in pitch attitude (nose down) and countered it with elevator input to maintain the intended climb speed. Subsequently, the rope was either released by the glider pilot or broke. The tow pilot continued the climb normally and reeled in the rope using the electric winch. However, due to several knots in the rope, it could not be fully retracted. The pilot executed a steep approach to runway 34 to avoid obstacles with the trailing rope and landed without incident.
Aircraft and Pilots
The towplane, a Robin DR 400/180 R (HB-EXU), was owned and operated by Alpine Segelflugschule Schänis AG. The pilot, a Swiss citizen born in 1982, held a private pilot license (PPL(A)) with 273:52 hours total flight time, including 158:12 hours on type. The glider, a Duo Discus (HB-3416), was owned and operated by Segelfluggruppe Lägern. Its pilot, a Swiss citizen born in 1960, held a glider pilot license with 468:23 hours total, including 51:31 hours on type.
Aftermath
Damage to the towplane consisted of a broken tow rope. The glider sustained no damage. There was no third-party damage. Both pilots sustained no serious injuries (classified as lightly or not injured). The Swiss Accident Investigation Board (SUST) issued a summary report based on available statements, noting the canopy opened for unknown reasons and that the passenger possibly interfered with the lock.