What happened
On September 29, 1968, a Beechcraft Musketeer Sport III, registration HB-ENM, was performing a repositioning flight from Altdorf to another airfield. The aircraft was carrying the pilot and three passengers.
During the takeoff roll from a field near Altdorf, the pilot encountered ground conditions that were significantly softer than previous flights due to recent heavy rainfall. The pilot initiated the takeoff without extending the flaps. As the aircraft approached the end of the runway, the pilot deployed the flaps to the 15-degree position in an attempt to lift off. The aircraft struggled to gain sufficient altitude and briefly touched the ground again.
As the aircraft attempted to clear obstacles, it struck two wire fences running alongside a road. The right main gear and the right wingtip made contact with the fencing. Following the collision, the pilot reduced power, and the aircraft came to a stop on the terrain approximately 17 of meters from the roadway. All four occupants escaped the incident without injury, though the aircraft sustained substantial damage.
The investigation
The investigation examined the aircraft's maintenance history, the environmental conditions, and the pilot's takeoff procedures. Investigators noted that the aircraft had undergone a 100-hour inspection just two days prior to the accident and showed no signs of mechanical unairworthiness.
Analysis of the weather and ground conditions revealed that significant rainfall in the preceding weeks had raised the groundwater level, resulting in a soft, saturated runway surface. While the pilot had successfully operated the aircraft from the same location the previous day with a headwind, the lack of wind and the increased surface friction on the day of the accident significantly extended the required takeoff distance.
Findings
- The primary cause of the accident was the improper use of flaps during takeoff. The pilot failed to follow recommended procedures for soft-field operations, which would have provided necessary lift.
- The aircraft failed to reach a sufficient airspeed to maintain a safe climb gradient due to the combination of high rolling resistance from the soft ground and the lack of a headwind.
- The pilot's takeoff configuration did not account for the degraded surface conditions, which necessitated a different flap setting to ensure obstacle clearance.
- The aircraft's weight and center of gravity were within limits, and there was no evidence of engine issues such as carburetor icing.