Location: Approximately 6.5 NM northwest of Yellowknife airport (YZF)
Status: Investigation Complete
While supporting Exercise ARCTIC RAM, Griffon CH146453 was conducting a night familiarization in the approved Low Flying Area. On the return to CYZF, while practicing low level flying, the aircraft overflew a lake and cut three high-tension power lines with the wire strike protection system at 54 feet (ft) above ground level (AGL) approximately 6.5 nautical miles (NM) north-west of CYZF disrupting electrical power to the city of Yellowknife. In the ensuing post-impact confusion, the crew then allowed the helicopter to descend to approximately 6 to 21 ft AGL before they conducted a climbing 180-degree turn, inadvertently overflying the same power line again. The helicopter returned to CYZF from the north, overflew the airfield, hover-taxied to the ramp and shut down. The aircraft sustained B category damage.
|19 feet - Distance between upper shielding cables and lower conductor wires|
Without the use of a checklist during a poor mission brief, the investigation found that the crew was not adequately prepared for this flight. No map or route reconnaissance of the area was completed, however, they still conducted unplanned low level flying in an unfamiliar area without reference to a map. After having completed their training, on the return to CYZF the crew chose to fly north of their intended route to conduct this low level flying training. Their perception of this mission as a low risk/low threat flight, their expectations regarding the distant location and large size of the transmission line, and their low state of arousal led to a reduced vigilance that contributed to a breakdown of visual scan. Due to this breakdown, combined with the lack of familiarity with the northerly flight path and a distracting discussion on simulated emergency considerations, the crew experienced geographical disorientation that precluded them from manoeuvring in time to see and avoid the transmission line.
Post-accident, the exercise low level flying altitude was raised to 500' AGL, errors with maps were corrected and the Commander 1 Wing provided direction on proper pre-flight planning, reconnaissance procedures, wire strike avoidance training, flight authorization procedures and supervision of inexperienced crews.
Safety recommendations include reviewing directions to Flight Authorizing Officers and to crews in the event of aircraft damage sustained in flight. Defence Research Development Canada was asked to review aircrew post-deployment/post-high operational tempo risk factors and human performance training tools to develop risk mitigation and coping strategies for RCAF implementation. Other recommendations include the implementation of a mission acceptance and authorization process for all CF fleets, inspection procedures of crew life support equipment, guidance to Flight Surgeons when dealing with civilian hospitals and post-occurrence testing of night vision goggles.