What happened
On April 11, 1962, a student pilot was conducting a solo training flight in a Rhönlerche II glider, registration HB-696, near the Bern-Belpmoos airfield. The flight began with a winch launch and instructions to perform thermalling maneuvers. After the pilot released from the winch, he began searching for lift. During this phase, the aircraft's airspeed dropped significantly below the required parameters.
As the pilot approached the airfield, he attempted to execute a standard landing pattern. Although he briefly increased his speed to approximately 90 km/h, he subsequently reduced it to roughly 60-65 km/h just before initiating a 90-degree left turn. During this turn, the pilot deployed the landing flaps, which caused a rapid descent rate of over 2 meters per second. Realizing that the remaining altitude was insufficient to clear local obstacles and complete the standard approach, the pilot attempted to divert for an off-field landing toward Belp. However, while executing this turn, the aircraft stalled and struck the ground at a steep angle, causing the glider to overturn.
The investigation
The investigation examined the flight student's training history, the aircraft's maintenance status, and the sequence of maneuvers leading to the impact. Investigators noted that the student had been performing satisfactorily in previous training sessions but had received criticism regarding low approach speeds in earlier flights that same morning. The investigation also looked into the technical state of the HB-606, noting that while it was a relatively new aircraft, the airspeed indicator lacked required limit markings. Furthermore, the investigation reviewed the pilot's focus on the variometer, which may have led to an unintentional reduction in airspeed while attempting to maintain climb rates.
Findings
- The primary cause of the accident was an insufficient airspeed during the landing approach, leading to a stall.
- The pilot's decision to deploy landing flaps at a low speed significantly increased the rate of descent, making the planned approach impossible.
- The student pilot likely focused excessively on the variometer to maintain lift, which resulted in a loss of airspeed awareness.
- The lack of red limit markings on the airspeed indicator of the HB-696 may have contributed to the pilot's failure to recognize the dangerous speed decay.
- The pilot experienced a minor concussion, while the glider sustained heavy damage and was rendered unusable.