What happened
On May 31, 1959, at approximately 15:36, a Rhönadler 32 glider, registration HB-312, departed from Samedan for a training flight. The pilot, who was relatively new to this specific aircraft type, had completed a circuit around the airfield earlier that afternoon. At roughly 16:00, while flying at an altitude of approximately 2,700 meters near Piz Mezzaun, the aircraft suffered a catastrophic structural failure. Witnesses observed the aircraft's wings and fuselage separating in mid-air and falling to the ground at different locations. The aircraft was completely destroyed upon impact, and the pilot was killed.
The investigation
The investigation examined the wreckage and the flight conditions leading up to the breakup. Investigators analyzed the debris to reconstruct the sequence of the failure, noting that the lower right connection fitting between the two wing halves tore first. This triggered a chain reaction where the right wing-to-fuselage connection broke out of the fuselage, and the left wing connection bolt was pulled out. This caused the main spars to burst under torsion.
Technical examinations of the HB-312 revealed that the aircraft belonged to a load factor group with limited strength. While the general condition of the aircraft was good, investigators identified a poor weld at a secondary location on the wing attachment, which may have reduced the structural safety factor. The investigation also considered the pilot's experience, noting that while highly qualified in other gliders, he had no prior experience with aircraft equipped with a pendulum rudder, which makes the elevator highly sensitive at high speeds.
Findings
- The primary cause of the mid-air breakup was the significant exceeding of the allowable load factor while flying at high speed.
- A poor weld at a secondary wing attachment point likely contributed to the failure by reducing the structural strength of the connection.
- The pilot's lack of familiarity with the sensitive pendulum rudder may have led to overcontrolling the aircraft during maneuvers.
- Localized gusts in the mountainous terrain could have added additional stress to the airframe during a critical phase of flight.
- The pilot may have been unaware of the specific strength limitations of this aircraft class, as he had not reviewed the logbook entries regarding its certification limits.