What aircraft was involved and where did it happen?

The accident on 2015-06-26 involved a GROB TWIN ASTIR, at Nowy Targ (EPNT), PL.

What was the probable cause of the accident?

The incident was caused by the pilot failing to properly secure the rear canopy of the GROB TWIN ASTIR before takeoff, leading to its opening during the tow.

Cockpit Canopy Opening During Glider Tow at Nowy Targ

A glider's rear canopy opened during a towed flight, forcing the crew to release the towline and perform an emergency landing.

What happened

On June 26, 2015, a licensed glider pilot was conducting the fourth sightseeing flight of the day at Nowy Targ Airport (EPNT) using a GROB TWIN ASTIR glider. The flight was operated under the AOC of Aeroklub Nowy Targ with one passenger on board. The takeoff, performed behind a Jak 12 tow plane, initially proceeded without issue.

However, at an altitude of approximately 50 meters, the rear canopy of the glider opened unexpectedly. The pilot attempted to hold the canopy in place with one hand, which significantly hindered the ability to control the aircraft and maintain the correct position behind the tow plane. This difficulty was further compounded by strong thermal turbulence. As the glider rose above the tow plane, causing the aircraft to enter a dangerous nose-down attitude, both the glider pilot and the tow plane pilot simultaneously decided to release the towline.

Following the release, the glider pilot performed a turn back toward the airport. To regain full control and operate the airbrake lever, the pilot eventually removed the canopy entirely. The glider landed with a crosswind from a 90-degree heading, while the tow plane completed a full circuit and landed according to the standard takeoff pattern. There were no injuries to the pilot, the tow plane pilot, or the passenger, though the glider's rear canopy glazing was destroyed.

The investigation

The PKBWL examined the circumstances of the release and the subsequent flight maneuvers. The investigation confirmed that all pilot documentation and aircraft certificates were valid at the time of the incident. Furthermore, blood alcohol tests for the glider pilot, the tow plane pilot, and the passenger all returned negative results. The investigation focused on the mechanical failure of the canopy seal and the operational response to the sudden loss of aerodynamic stability.

Findings

The primary cause of the incident was the improper closure of the rear canopy by the pilot prior to takeoff, which allowed it to open under flight loads.
Severe thermal turbulence contributed to the difficulty in maintaining the glider's position behind the tow plane.
The simultaneous decision by both pilots to release the towline prevented a more serious collision or loss of control.