What happened
On 10 June 2005, a Robinson R4-4 Clipper II, registration G-SHAN, was performing a private flight near Chesham, Buckinghamshire. The aircraft had departed from a private farm site and was approximately five minutes into the flight when the pilot initiated a normal approach to land. During this approach, the pilot heard a slight noise while the helicopter was at an altitude of approximately 100 feet.
Upon landing, an inspection revealed that the main rotor mast fairing had been struck. The investigation determined that the aircraft had come into contact with one of a pair of telegraph wires that spanned a valley for approximately 900 feet. The wires were supported by poles located on either side of the field, which were largely obscured by trees and shrubs.
The investigation
The investigation examined the environmental conditions and the physical state of the wires. At the time of the incident, weather conditions were favorable, with visibility exceeding 10 km, light winds, and no significant cloud cover. However, the approach was made into the evening sun, creating a high-contrast environment between the bright sky and the darker ground vegetation.
The wires, which were green in color, were set against a similar green background of grass and trees. It was noted that the telegraph wires were made of corroded copper. While both wires were present, only one was severed by the rotor mast fairing; it was suggested that this may have been due to one wire sagging more than the other.
Findings
- The primary cause of the incident was the pilot's inability to visually identify the wires during the approach.
- The presence of the wires was masked by the green color of the cables against the green landscape.
- The evening sun created a high-contrast lighting condition that further hindered visibility.
- Trees and shrubs obscured the telegraph poles supporting the wires.