What happened
On April 22, 1979, a Morane MS 893 E, registration HB-EYH, was attempting a commercial sightseeing flight from the Hasenstrick private airfield in Dürnten, Switzerland. The aircraft was carrying a pilot and three passengers. During the takeoff roll on runway 11, the pilot applied full power, but the aircraft failed to become airborne by the expected distance of 250–300 meters.
As the aircraft reached the end of the runway, it continued to roll with the nose elevated and the tail skid making contact with the ground. Upon crossing a road perpendicular to the runway, the tail skid struck the pavement heavily, causing the aircraft to become airborne. However, due to insufficient airspeed, the aircraft could not maintain altitude while traversing the sloping terrain. Approximately 150 meters past the runway end, the aircraft struck a tree 25 meters below the airfield level. The impact caused the aircraft to roll and come to rest on its back. Two passengers sustained minor injuries, but the aircraft was destroyed.
The investigation
Investigators examined the runway conditions, weather data, and the pilot's preparations. The investigation established that the grass runway had been significantly softened by heavy rainfall, with 148 mm recorded in the 30 days prior to the accident. The aircraft was operating at a high weight of 1012 kg, near its maximum takeoff weight of 1050 kg.
Technical analysis of the wind conditions revealed that while the pilot observed a light western wind, there were gusts of up to 20 knots. Calculations based on the aircraft's manual indicated that even a moderate headwind component was absent, and a tailwind likely existed. Furthermore, the investigation looked into the pilot's rotation technique, noting that rotating too early may have increased aerodynamic drag and prevented the aircraft from reaching flying speed.
Findings
- The primary cause of the failed takeoff was a combination of unfavorable runway conditions, a tailwind, and insufficient flight preparation.
- The saturated, muddy state of the grass runway increased rolling resistance.
- The presence of a tailwind likely extended the required takeoff distance beyond the available runway length.
- The pilot's decision to rotate the aircraft at the expected 250-meter mark may have prevented the aircraft from reaching the necessary liftoff speed due to increased drag.