Introduction
On 28 June 1986, at 1420 local time, a SZD-51-1 Junior glider, registration HB-1816, crashed near Birrhard in the canton of Aargau, Switzerland. The female pilot, a 28-year-old Swiss citizen holding a glider pilot license with 31.58 total flight hours (1.24 hours in the previous 90 days), was seriously injured. The glider was destroyed, and minor crop damage occurred.
Flight History
The pilot departed from Birrfeld airfield at 1418 hours on a training flight under aero-tow. The takeoff and initial climb toward the east were normal. At approximately 500 meters past the runway end, near the N1 highway, the glider climbed higher than the towplane, forcing the tow pilot to correct his position. The glider then dropped below the normal tow position, disappearing from the tow pilot's mirror view. Shortly after, the tow pilot saw the glider slightly high and offset to the left. At that moment, at about 1000 meters above ground, the towline released from the glider, and the glider turned right. The tow pilot observed the glider turn approximately 120 degrees to the right before the descent steepened. After a full 360-degree turn, the glider struck the ground at an angle of about 60 degrees.
Findings
The pilot held a valid glider pilot license and was authorized for the flight. No evidence of pre-existing health issues was found; however, the pilot wore glasses, and a damaged pair was found in the cockpit. The pilot had retrograde amnesia and could not recall details. The glider was certified for flight, with weight and center of gravity within limits. No pre-existing defects were found. The trim was set in the nose-down range (about one-third from the forward stop). The towline was a hemp rope approximately 35 meters long, which was within the prescribed range of 40–60 meters for aero-tow (60 meters recommended for inexperienced pilots). The line was undamaged and subsequently reused. The nose release hook functioned properly. Weather conditions featured a high-pressure system with light east wind turbulence; no rotors were observed.
Analysis
The glider began oscillating shortly after takeoff. The pilot was unable to regain normal flight attitude and appeared to release the towline. The turnback attempt toward the airfield was initiated at low altitude. During the right turn, the glider's airspeed dropped below the minimum flight speed, leading to a stall. The low altitude prevented recovery. Contributing factors included the short towline (35 meters instead of the recommended 60 meters for inexperienced pilots), light turbulence, and the pilot's low flight experience (only 31 minutes on type in the previous 90 days).
Cause
The accident was caused by undershooting the minimum flight speed during a turnback after releasing from the tow aircraft shortly after takeoff.