What happened
While attempting to land at a remote site near Moosable, Ontario, an Aerospatiale AS 350 B2 helicopter, registration C-GOHY, struck guy wires supporting a communications tower. The pilot had originally intended to land in a nearby clearing, but after determining the ground was too soft, opted to use a driveway adjacent to the tower. To maintain visual contact with the landing zone, the pilot executed a sideways approach to the left.
During this maneuver, the main rotor blades struck two of the tower's upper guy wires at an altitude of approximately 100 feet. The impact caused significant damage to the blades, leading to a rapid descent. The aircraft struck the ground in an inverted position. The crash resulted in two serious injuries and one minor injury among the three occupants. While the pilot was unable to immediately exit the wreckage, the two passengers managed to extricate themselves and utilized a telephone at the site to summon an air ambulance.
The investigation
Investigators examined the aircraft's mechanical condition, the pilot's experience, and the environmental factors. The pilot was found to be experienced, properly licensed, and medically fit, with no history of fatigue or mechanical issues with the aircraft prior to the flight. The weather conditions were stable, with light winds and clear visibility.
Technical examination focused on the failure of the Emergency Locator Transmitter (ELT) to activate despite impact forces exceeding the G-switch threshold. Investigators discovered that the internal G-switch in the ELT had seized due to black powder residue, preventing electrical contact. Furthermore, the investigation noted that the single-axis nature of the switch meant that impact forces oriented differently from the switch's axis might not trigger activation.
Findings
- The primary cause of the accident was the pilot's decision to fly the helicopter sideways, which obscured the view of the approaching guy wires while focusing on the landing area.
- The structural damage from the wire strike rendered the aircraft uncontrollable.
- The ELT failed to activate because of a faulty, seized internal G-switch.
- The single-axis design of the ELT's G-switch is inherently limited when impact forces occur at angles different from the switch's orientation.