What happened
On May 14, 2021, at approximately 16:56 UTC, an ultralight helicopter, I-D407, a CH 7 Kompress Charlie, was flying at a very low altitude over the Římov reservoir near Velešín, Czech Republic. The pilot was navigating the valley by following the contours of the shoreline, maintaining an altitude of approximately 20 meters above the water level.
During the flight, one of the main rotor blades struck a low-hanging high-voltage phase conductor. The impact severed the wire, causing it to fall onto the banks of the reservoir and triggering a local power outage. The contact with the electrical line caused significant vibrations and degraded the controllability of the aircraft. The pilot immediately responded by climbing out of the valley and performing an emergency landing in a nearby field.
The investigation
The ÚZPLN investigation examined the aircraft, the site of the strike, and the electrical infrastructure. Forensic examinations of the main rotor blades confirmed they had been damaged by contact with the wire. Physical evidence at the scene showed that the conductor had been severed and found on both banks of the reservoir. The investigation also reviewed witness statements from local residents who observed several ultralight helicopters flying low over the water and noted the timing of the power failure.
Findings
- The pilot was flying well below the minimum VFR altitude requirements of 150 meters (500 feet) above the ground or water.
- The aircraft was flying at an altitude of approximately 20 meters, which was level with the height of the lowest electrical conductor.
- The pilot was unaware of the presence of the high-voltage lines, which were difficult to identify against the dark, wooded background of the reservoir banks.
- The primary cause was the decision to fly below the minimum permitted VFR altitude at a height that was in direct collision course with the power lines.
- The impact caused severe vibrations and compromised the aircraft's handling, though the pilot's decision to land immediately prevented a more serious accident.