What happened
On July 12, 2014, a private flight training session ended in an off-field landing near Hällbybrunn, Sweden. The flight began with a standard tow to 800 meters, but after failing to find rising thermals, the pilot attempted to return to the home airfield. During the return leg, the pilot realized the glide slope was insufficient to reach the runway and instead targeted a nearby agricultural field.
As the aircraft descended, the pilot noted a significant increase in the rate of descent and felt the glider shaking. The landing took place in a field with tall crops, which created high resistance. This caused the ASW-27 to enter a ground loop, a rapid horizontal rotation on the ground. The impact was severe enough that the rear section of the fuselage partially separated from the rest of the aircraft. The pilot was able to exit the glider without physical injuries.
The investigation
Investigators analyzed GPS logger data to reconstruct the final minutes of the flight. The data revealed that the pilot turned back toward the airfield at an altitude of 559 meters. During the turn, the descent rate increased sharply and remained high for the rest of the flight. Over a 3.5 km stretch, the aircraft lost 488 meters of altitude, resulting in a glide ratio of approximately 1:7.
While modern gliders are certified to maintain certain glide ratios even with air brakes extended, a ratio of 1:7 is exceptionally low for this high-performance model. Experienced pilots noted that such a high descent rate typically only occurs when the air brakes are deployed. The pilot's report of the aircraft "shaking" further supported the conclusion that the air brakes were active.
Findings
- The primary cause of the excessive height loss was that the pilot likely confused the air brake lever with the flap lever, resulting in the flight being conducted with the air brakes extended.
- A contributing factor was the pilot's limited experience with gliders equipped with flaps, which hindered their ability to recognize the abnormal flight conditions caused by the accidental deployment.
- The pilot's decision to avoid using flaps or landing gear due to low altitude contributed to the severity of the ground loop upon landing in the tall crops.