What happened
On May 27, 1972, a private VFR flight involving a Minicab GY 20-1, registration HB-SUZ, was conducting a return trip from Bern to Olten. The pilot, accompanied by a passenger, had previously landed in Bern earlier that day, where they encountered difficult wind conditions that necessitated an aborted landing attempt.
During the return approach to the Olten airfield, the aircraft encountered severe weather characterized by heavy turbulence and strong, gusty winds reaching speeds between 15 and 37 knots. While on the final approach to runway 23, the aircraft began to deviate from the standard approach path. As the pilot entered the downwind leg, the aircraft experienced a significant loss of airspeed. The aircraft entered a spin-like rotation at an altitude of approximately 100 to 200 meters. Although the pilot managed to recover the rotation after only one or two turns, the remaining altitude was insufficient to prevent the crash. The aircraft struck a grassy area with its left wing and came to rest near a residential building, resulting in the death of the pilot and serious injuries to the passenger.
The investigation
Investigators examined the aircraft, the wreckage, and the meteorological conditions at the time of the accident. The investigation included witness statements from pilots at the Olten airfield and local authorities. The aircraft, HB-SBZ, was found to be well-maintained, with all weight and balance parameters within legal limits. The engine and propeller showed no signs of pre-existing mechanical failure, though the deformation of the propeller indicated significant engine RPM at the moment of impact.
Medical examinations of the pilot revealed a history of chronic coronary heart disease, though investigators noted that the pilot's recent flight medical examinations had cleared him for duty. The investigation also reviewed the wind conditions, noting that the gusts and turbulence present during the landing phase were extremely high for a light aircraft of this type.
Findings
- The primary cause of the accident was the underspeeding of the aircraft below its minimum flying speed due to the presence of severe turbulence and critical wind conditions.
- High wind gusts caused an increase in the aircraft's bank angle, which significantly raised the required minimum stall speed.
- The pilot was operating in a highly stressful environment due to the extreme weather, which made maintaining the necessary airspeed margin difficult.
- The aircraft was in good mechanical condition and was properly maintained and loaded.