What happened
On the afternoon of June 6, 1965, a pilot performing aerobatic maneuvers in a Bücker 131 "Jungmann", registration HB-UTS, approached the Yverdon airfield for a landing. The flight was part of a preparatory aeronautical instruction course.
At approximately 15:20, the pilot touched down on runway 23, roughly 40 meters from the threshold and near the right edge of the runway. As the aircraft taxied along the concrete runway markers, the right wing struck several sheep that had wandered onto the landing area. The impact caused the landing gear to collapse, forcing the aircraft to come to a halt on its belly approximately 127 meters from the start of the runway. The collision resulted in four sheep fatalities and minor injuries to the pilot.
The investigation
The investigation examined the airfield's operational procedures regarding livestock. At the time, the airfield operator had authorized a local butcher to graze sheep on the grounds. While the shepherd had attempted to move the flock away from the runway using dogs, several stragglers remained in the tall grass near the runway markings. The investigation also reviewed the pilot's experience and the visibility conditions of the aircraft during the landing phase.
Findings
Investigators determined that the pilot's position on the far right edge of the runway was not due to error, noting that the pilot's limited experience and the poor forward visibility inherent in the Bücker 131 "Jungmann" made it difficult to spot the animals in the tall grass.
However, the primary cause was identified as the presence of livestock in a restricted zone. The investigation found that the sheep were part of a flock that was insufficiently supervised. Although instructions existed to keep animals away from the runway during flight operations, the oversight by both the shepherd and the airfield authorities was inadequate, allowing animals to remain in an area that should have been clear of obstacles.