What happened
On 28 May 2016, a Robinson R44 Raven I, registration G-HWKS, was conducting a private flight near Ballyshannon, Co. Donegal. The flight, which included the pilot and three passengers, was intended to move from Belleek, Northern Ireland, to a hotel in Lough Eske, but included a detour to an agricultural field for photography purposes.
As the pilot approached the landing site, they noted electricity poles positioned within nearby trees. While attempting to land in the middle of the field, the pilot was alerted by a passenger to the presence of wires. Despite an immediate attempt to maneuver the aircraft to the left, the main rotor blades struck and severed two 10 kV copper-stranded electrical wires. The impact caused the tail of the helicopter to swing downward and to the right, though the pilot was able to regain control and perform a safe landing. There were no injuries and no fire, though the strike caused a power loss to several local properties.
The investigation
The AAIU examined the aircraft and the landing site, noting that the field featured a significant upward slope toward the landing direction. Investigators inspected the damage to the G-HW 44's main rotor blades, finding various indentations, scrapes, and torn skin material on the leading and trailing edges.
Furthermore, the investigation looked into the pilot's decision to continue flying the aircraft for a short distance following the strike. The pilot had performed a cursory inspection with a passenger—a helicopter engineer—and determined the aircraft could fly back to the original departure field. The investigation also reviewed the aircraft's maintenance records and compliance with Airworthiness Directives (AD) regarding rotor blade inspections.
Findings
- The primary cause of the accident was the main rotor blades striking overhead electrical wires that were traversing the field.
- The visibility of the wires was likely compromised by the physical limitations of the human eye, the lack of contrast against the background, and the fact that the field's upward slope may have placed the wires below the pilot's horizon.
- The pilot's decision to operate the helicopter for a subsequent flight despite visible damage to the main rotor blades was considered an imprudent course of action, especially given the potential for catastrophic failure.
- The investigation noted discrepancies in the aircraft's technical documentation, specifically regarding the referencing of superseded Airworthiness Directives.