What happened
On May 5, 1976, a K 6 CR glider, registration HB-678, departed from Birrfeld airfield for a 300 km circuit flight. After being towed to an altitude of 1,000 meters, the pilot released the tow rope. Despite a weather forecast suggesting moderate to good thermals, the pilot encountered very weak lift, resulting in a steady descent of approximately 1 m/s while flying over the Aaretal region.
After roughly 20 minutes of flight, the pilot identified a potential landing field near the village of Kienberg. Seeking better lift, the pilot attempted to circle the area to find rising air. However, after another 10 minutes of searching, the pilot was forced to commit to a landing. While maneuvering over the village to align with the chosen field, the pilot noticed a brief increase in lift, prompting a turn to the east to seek more thermals. This maneuver resulted in a sudden increase in sink rate to 2.0–2.5 m/s. In an attempt to tighten the turn and reach the landing direction quickly, the pilot undershot the minimum flying speed, causing the aircraft to stall.
The glider's right wing struck a tree and a telephone pole before the aircraft entered a descending spin. The HB-678 crashed between buildings on a village street, coming to rest near a garden wall. The pilot suffered severe injuries, and the aircraft was destroyed.
The investigation
Investigators examined the pilot's credentials, noting he was a licensed glider pilot with over 222 flight hours, though he had no prior experience with off-field landings. The aircraft was found to be in a valid regulatory state, with weight and balance within limits and no evidence of mechanical failure.
Analysis of the barogram confirmed that the aircraft was in a steady descent for much of the flight, with only two minor instances of altitude gain. The investigation also reviewed the meteorological data, noting that the thermal forecast was overly optimistic compared to the actual conditions experienced at the time of the accident.
Findings
- The weather forecast for thermal activity was too optimistic, a fact the pilot did not realize until late in the flight.
- The pilot continued the flight toward the Jura hills despite insufficient altitude reserves and precarious thermal conditions.
- The decision to attempt a landing was made too late.
- An attempt to maneuver over the village to find rising air was both futile and dangerous.
- The aircraft's speed dropped below the minimum required for flight during a tight turn, leading to a wing stall.