Accident Overview
On June 4, 2001, a Bell 47G-4A helicopter engaged in a private flight from Böhlen to the Merseburg airfield. Approximately 20 minutes after departure, the helicopter collided with an overhead power line. The pilot managed to perform an emergency landing in a cornfield about 300 meters beyond the line. The helicopter sustained serious damage, and the pilot suffered cuts.
Investigation Findings
Examination of the wreckage revealed that the power line contacted the upper portion of the cabin, shattering the glazing. Contact and burn marks were also found on the lower part of the left fuel tank. One of the two rotating control rods connecting the swashplate to the rotor head was bent and pressed against the rotor mast.
The power line was a three-conductor 20 kV line consisting of aluminum cables approximately 3 cm in diameter. All three cables were severed upon impact. The line crossed the Saale River at a location where both banks were lined with tall trees. On the west bank, a 16 m lattice mast supported the line; on the east bank, a 13 m concrete mast was used. Both masts ended below the height of the surrounding trees, with a span of 100 m between them.
Pilot and Witness Statements
The pilot reported that he intended to climb to a higher altitude before reaching Merseburg. While doing so, he inadvertently increased the collective pitch so significantly that main rotor rpm dropped sharply. To counteract the rpm decay, he initiated a steep descent and a right turn. Once the rpm stabilized, he transitioned to level flight and subsequently collided with the power line.
Witnesses observed the helicopter in a stationary hover over the Saale River before it flew off and struck the line. Another witness estimated the helicopter's height at 50–60 m shortly before the accident.
Weather conditions recorded at nearby Leipzig airport included wind from 250° at 9 knots, visibility greater than 10 km, broken clouds at 2200 ft, and rain. The pilot stated that his flight altitude was not restricted by meteorological conditions.
Assessment
Wreckage evidence indicated that the helicopter was in normal flight attitude when it impacted the power line. The first contact occurred with a main rotor blade and the upper cabin glazing. The power line ran below the treetops at the wooded accident site, and the supporting masts did not extend above the trees. Overhead lines are generally difficult to detect from a helicopter, especially when masts are not visible and the cables are set against a dark forest background. The risk of encountering power lines during low-altitude flight is known to all helicopter pilots.
The pilot's explanation for initiating a steep descent and right turn to recover rotor rpm was not considered plausible. It would be unusual to apply such a large collective pitch increase during cruise that the rpm dropped unacceptably. Furthermore, the correct procedure to restore rpm is to lower the collective while reducing speed (flare), making the described maneuver unsuitable.
Conclusions
Based on the evidence, it was concluded that the pilot flew along the Saale River below treetop height without a compelling reason and failed to recognize the power line in time.