What happened
On the afternoon of August 1, 1963, a pilot conducted a test flight in a Druine D-32 Turbulent, registration HB-SOI, departing from Altenrhein airfield. Following a recent 50-hour inspection, the pilot proceeded to fly toward Rorschach and then over Lake Constance toward the mouth of the Rhine.
During the flight, the pilot performed low-altitude maneuvers, including steep turns with rapid descents, specifically to test the effects of ground effect on maximum airspeed. While maneuvering near the shoreline in the area of the Rhine's mouth, the aircraft's right wingtip and right landing gear struck the water. The impact caused the aircraft to decelerate sharply and subsequently capsize near a boat. The pilot sustained only minor abrasions, but the aircraft was destroyed.
The investigation
The investigation, conducted by the Swiss accident investigation office in coordination with Austrian authorities, examined the pilot's experience, the aircraft's mechanical condition, and the flight maneuvers. The pilot had approximately 70 hours of total flight experience, with about 20 hours logged in this specific aircraft type. The Druine D-32 Turbulent was a single-seat, wooden, low-wing aircraft powered by a modified 34 hp engine. The investigation found no evidence of medical issues affecting the pilot or technical failures within the aircraft. Weather conditions at the time were favorable, characterized by high pressure and light winds.
Findings
- The pilot misjudged the altitude during low-level flight over the water.
- Performing steep turns and rapid descents at extremely low altitudes over a large water surface makes height estimation significantly more difficult.
- The pilot's limited flight experience made the execution of such high-risk maneuvers particularly dangerous.