Summary
On Sunday, 10 July 1966, the aircraft HB-UTG, a Bücker 131 (Jungmann), was taking off for a return flight from an airshow at Lenk im Simmental. During the takeoff, the landing gear hit the wires of a high-voltage power line. The aircraft then sank and impacted the ground, suffering severe damage and subsequent fire. The two occupants were not injured.
Investigation
The investigation was completed on 26 October 1966. The pilot, born in 1919, held a professional pilot license and a special permit for low-level aerobatics. He had about 1650 flying hours, with 300 hours on the accident type. The passenger was born in 1932. The aircraft was owned by Regionalflugplatz Jura-Grenchen AG. It was a single-engine open two-seat biplane, powered by a Hirth HM 504 A2 engine. The takeoff weight was 610 kg, within limits, with the center of gravity within limits. The airfield, Neufeld Lenk, at about 1060 m elevation, had a trapezoidal shape with a longest side of 450 m. Two power lines crossed north of the field: the first at about 10 m height, 540 m from the start; the second at about 12 m height, 620 m from the start. Weather was nearly calm with light north wind and temperature about 16°C.
Events
The airshow was organized by Fluggruppe Obersimmental. Initially, the permit was denied due to obstacles, but later granted on 8 July 1966. The pilot was asked to perform aerobatics two days before. He arrived at 1456 hours and performed an aerobatic flight at 1609 hours with a takeoff weight of about 550 kg, easily clearing the power lines. At about 1800 hours, he prepared for the return flight with a passenger. He selected the lighter of two volunteers and limited fuel to 50 liters. The takeoff began at 1815 hours. The aircraft rolled longer than expected. At about three-quarters of the runway length, he initiated rotation. It lifted off about 80 m before the end, briefly touched down again, then climbed steeply to clear the first power line about 120 m past the end. The first line was cleared narrowly, but the second, about 75 m behind and 2 m higher, was struck by the landing gear, breaking two of the three copper wires. The aircraft then dropped and impacted the ground hard, sliding on its belly. The occupants exited quickly as a fire started, and the aircraft burned completely.
Damage
The aircraft was destroyed. The high-voltage line was damaged, with a cost of 485.90 Swiss francs. No third-party damage on the ground.
Discussion
The flight manual for HB-UTG indicated that at maximum weight (670 kg) and zero wind, the takeoff distance to 15 m at 1000 m elevation is 735 m. The actual takeoff weight was 610 kg, but the wind was nearly calm. The pilot did not calculate the expected takeoff distance.
Probable Cause
The accident was caused by the pilot taking off with a load not appropriate for the field conditions and subsequently colliding with a high-voltage line while in a stalled condition.