Summary
A Rhönlerche II 164 glider, registration HB-696, operated by ALPAR A.G., crashed on 11 April 1962 at approximately 1425 hours local time during a landing approach at Bern-Belpmoos airfield in Switzerland. The student pilot, born in 1943 and holding a learner's permit for motor and glider flight, was conducting a solo training flight. The glider was heavily damaged and the pilot sustained a mild concussion resulting in more than four days of incapacity for work.
Investigation
The accident was promptly reported to the Bureau for Aircraft Accident Investigation, which dispatched an investigator to the site. The glider, built in 1961 by A. Schleicher of Poppenhausen, Germany, had been factory-new and imported in June 1961. It received a restricted operating permit on 29 March 1962, valid for test flights over Belpmoos airfield. The test flight program was not yet complete; only one check flight with half load had been conducted on 7 April 1962, which indicated normal flight characteristics and a stall speed of approximately 50 km/h. The glider was subsequently used in the ALPAR flight school on 9–11 April 1962 despite the incomplete test program and lack of airspeed indicator markings.
Aircraft and Pilot
The glider had an empty weight of 223 kg and a maximum takeoff weight of 400 kg. The pilot had accumulated 56 launches totaling 6.5 flight hours, including 5 hours 53 minutes during a previous training course in October 1961. He had largely flown a different Rhönlerche (HB-572) prior to this course. On the day of the accident, he had performed two winch launches earlier that morning: one dual check flight where his glide was criticized as too slow, and one solo flight where his approach was deemed too slow and his glide from a turn too low.
Sequence of Flight
After a theoretical lesson emphasizing approach speeds of 85-100 km/h, the pilot was launched at 1416 hours in a tow to 450 meters above the airfield. He was instructed to practice thermalling and land by 1515 hours. He released in a thermal and began circling, but his speed was about 70 km/h instead of the required 80-85 km/h. After gaining some altitude, the thermal dissipated, and he continued searching for lift at about 65 km/h. The flight instructor observed the glider flying slowly with a high angle of attack and uncoordinated turns.
When the pilot reached about 300 meters, he returned toward the airfield. Approaching the downwind leg at about 190 meters, he accelerated to roughly 90 km/h. At approximately 500 meters from the field, he still had 150 meters of altitude and delayed turning final until reaching a landmark 700 meters out. Concerned that his speed of 90 km/h seemed too high, he reduced it to 60-65 km/h and initiated a 90-degree left turn. During the turn, he deployed the airbrakes, causing a sink rate of over 2 m/s. After the turn, he retracted the airbrakes but the sink rate did not decrease. While preparing a further 90-degree turn to final, the glider stalled from a height of about 10-15 meters and struck the ground in a steep nose-down attitude.
Probable Cause
Insufficient airspeed.