What happened
On April 6, 2003, a Schleicher ASK 21 glider, registration PH-660, was conducting a local instructional flight from the Terlet gliding center. The crew consisted of an instructor in training and a student pilot, for whom this was only the third takeoff. After approximately one hour of flight, the crew began their approach to the airfield.
During the approach, the aircraft encountered significant upward movement while on the lee side of the wind. To maintain a target altitude of 200 meters at the low connection point, the instructor instructed the student to temporarily deploy the spoilers. The instructor had opted for a wide approach pattern to provide the student with a longer final leg, making it easier to manage speed and altitude. After turning onto the crosswind leg, the instructor took control of the aircraft.
As the aircraft turned onto the final leg, the spoilers were opened to adjust the glide slope. However, the glider began flying directly toward a line of trees that obstructed the landing area. Realizing the descent was too steep, the instructor closed the spoilers and attempted to increase airspeed to clear the trees. When it became clear that clearing the treeline was impossible, the instructor steered toward a gap with lower treetops and attempted to pull up to avoid the thickest trunks. Due to insufficient forward speed, the right wing struck branches, causing the aircraft to roll more than 90 degrees and land upside down.
The investigation
The investigation focused on the decision-making process regarding the approach pattern and the impact of wind conditions. The instructor was aware that wind speeds had increased and that windshear was a known factor behind the treeline. While the instructor had experience managing such conditions by flying a tight circuit, he chose an unconventional, wider pattern for this flight.
Findings
- The instructor chose an unusually wide approach pattern to assist the student, which departed from his standard practice of flying a tight circuit in similar wind conditions.
- The flight speed during the approach was 100 km/h, whereas a speed of 110-120 km/h would have been more appropriate given the weather.
- The instructor underestimated the impact of the wind and the resulting descent rate while on the final approach leg.
- The aircraft sustained unrepairable damage, and while the instructor was uninjured, the student sustained light injuries.