What happened
On February 15, 1965, a Beechcraft F-35 "Bonanza", registration HB-EFB, was preparing for a private flight from La Chaux- de-Fonds to Madrid with two passengers on board. The airfield was covered in approximately 70 cm of old snow, with a fresh layer of about 10 cm having fallen recently. Because the airport's snowplow was unavailable, the pilot requested that a small tractor clear only a narrow strip of the runway.
By 11:45 HEC, a strip measuring 15 to 20 meters in width had been cleared. This operation left high walls of snow, reaching approximately one meter in height, on both sides of the cleared path. The pilot inspected the runway and deemed it suitable for departure. During the takeoff roll at 15:40 HEC, the aircraft accelerated normally until it reached the two-thirds mark of the runway. At this point, the aircraft suddenly drifted to the left. Unable to maintain the centerline, the pilot reduced engine power, but the aircraft continued to veer into the uncleared area, striking the snowbanks and coming to a halt in a nose-up position.
The investigation
The investigation focused on the runway conditions and the decision-making process regarding the takeoff. Investigators examined the state of the runway, noting that the cleared width was insufficient given the aircraft's 10-meter wingspan. The investigation also reviewed the pilot's previous history, noting a similar incident involving the same aircraft, HB-EFB, during a failed takeoff in thick snow in January 1963.
Findings
- The aircraft's left wing likely struck the snow embankment at the edge of the cleared strip.
- The cleared runway width of 15 to 20 meters provided insufficient safety margins for a low-wing aircraft with a 10-meter wingspan.
- The use of a small tractor to clear the path resulted in an uneven surface, which contributed to the aircraft's loss of directional control.
- There were no injuries to the pilot or the two passengers, though the aircraft sustained significant damage to the propeller, nose wheel, and wing leading edges.
Safety action
- The commission concluded that the accident was caused by the pilot's decision to proceed with the flight despite the runway conditions not providing an adequate margin of safety.