What happened
On April 12, 1961, during a glider training camp organized by the Winterthur Gliding Group near Frauenfeld, two student pilots were performing required thermal soaring flights. The first aircraft, a Karpf Baby with registration HB-5SB, departed at 12:39. Shortly after, a second aircraft, a Grunau Baby IIB registered as HB-497, departed at 12:58.
While operating in the thermal lift area north of Weiningen, both aircraft were performing left-hand turns. At approximately 13:06, at an altitude of roughly 1,200 meters, the HB-497 collided with the HB-512 from a low-rear position. The impact was severe, with the nose of the lower aircraft striking the trailing edge of the upper aircraft's right wing.
The collision caused the HB-512 to lose its right wing and enter an uncontrollable descent, eventually crashing into a meadow. The pilot of the HB-512 managed to escape using a parachute and remained uninjured. The HB-497 sustained heavy damage to its fuselage and left wing, entering a steep dive before crashing into an orchard. The pilot of the HB-497 sustained fatal head and neck injuries during the collision and was unable to use a parachute.
The investigation
The investigation examined the flight paths, the technical condition of both gliders, and the environmental conditions. The weather was clear with good visibility and light winds. Both aircraft, the Karpf Baby and the Grunau Baby IIB, were found to be in good mechanical condition with no technical defects contributing to the accident.
Investigators also reviewed the flight experience of both pilots, noting that both were students undergoing training. The investigation looked into the possibility of sun glare or instrument over-concentration as contributing factors. It was noted that the pilot of the HB-512 had observed the other aircraft earlier but had assumed the higher aircraft would either leave the thermal or pass at a safe distance.
Findings
- The primary cause of the collision was insufficient airspace surveillance by the pilot of the HB-497.
- The pilot of the HB-497 likely failed to maintain adequate visual contact with the aircraft above him.
- There was a possibility that the pilot's attention was overly focused on flight instruments, a common issue during the training phase.
- The pilot of the HB-497 may have incorrectly assumed that because other aircraft were not present during the initial tow, the thermal area would remain clear.
- While the pilot of the HB-512 was not maintaining a climb due to a wide turn, this was not considered a primary cause of the accident.