Occurrence
An Aerospatiale AS 350 B2 helicopter, registration C-GOHY, serial number 2589, operated by Hydro One Networks Inc., was attempting to land at a remote site near Moosonee in northern Ontario. The pilot selected a driveway near a communications tower, which was supported on three sides by multiple guy wires. The pilot approached the driveway by flying the helicopter sideways to the left while maintaining forward visual contact with the landing area. As the helicopter moved sideways, the main rotor blades struck two of the top guy wires at a height of about 100 feet above ground level. The rotor blades were substantially damaged, and the helicopter quickly descended and struck the ground in an inverted attitude.
Occupants and Injuries
The two passengers, Hydro One employees, were able to extricate themselves but could not extricate the pilot. One passenger used a telephone at the site to call the air ambulance unit in Moosonee. The air ambulance crew extricated the pilot and transported all three to a local hospital. One hydro worker received minor injuries; the pilot and the second hydro worker were seriously injured. There was no fire. The emergency locator transmitter (ELT) did not activate.
Pilot and Aircraft Information
The pilot held a valid commercial helicopter licence and a current medical certificate. The pilot was familiar with the type of operation and the area. The pilot had been off-duty for approximately 15 hours prior and had flown less than three hours the previous day. The occurrence flight was the first of the day, about 40 minutes in duration. The helicopter had been maintained in accordance with regulations and manufacturer documentation; no mechanical abnormalities were reported.
Landing Site Selection
Initially, the pilot intended to land on a wide clearing near a switching station. While hovering to land, the pilot assessed the ground as too soft. The only other suitable area was the driveway near the communications tower, which was more confined with mature brush lining the sides but wide enough for the helicopter.
Weather Conditions
Weather at the time: wind from the west at 8 to 10 knots, partly cloudy sky, temperature approximately 23°C.
Findings
No indications of weather or mechanical abnormalities were involved. The pilot was familiar with the site and experienced. The selected landing area, though confined, was suitable. The pilot's decision to approach sideways restricted his view of the approaching guy wires, significantly increasing the possibility of contact between the main rotors and the wires. The structural damage rendered the helicopter uncontrollable; it became inverted and entangled on a wire during descent. It is possible that the wire entanglement reduced impact forces and prevented further injuries.
The ELT did not activate. The type of G-switch used was a single-axis, ball and spring type, which activates only if impact force is in the same direction as the switch orientation. During examination, black powder residue was found, and the switch was seized, preventing electrical contact. The ELT failure did not affect rescue due to available phone service.
Probable Cause and Risk Findings
The Transportation Safety Board found that the helicopter struck the guy wires as a result of being flown in a left sideward direction, which prevented the pilot from viewing the approaching tower guy wires from his position in the right front seat while focused on the restricted landing area. Additionally, the single-axis G-switch is not effective when impact forces are at angles substantially different to switch orientation, and the ELT failed due to a faulty internal switch susceptible to deterioration over time.
Safety Action
Transport Canada will contact Narco and ACK Technologies Inc. to seek publication of a Component Maintenance Manual amendment mirroring a Select Controls Inc. recommendation.