The Transportation Safety Board of Canada has determined the primary cause of a Eurocopter AS350 B2 crash in January 2015 to be increased cable tension during stringing operations, which led to the aircraft performing a "dynamic rollover."
The aircraft was operated by Airspan Helicopters Ltd., and its pilot was conducting aerial work about 11 nmi from Key Lake Airport, Saskatchewan. According to the board's report, the pilot was pulling feeder cable through electrical transmission towers using a "needle." After the pilot completed work on 10 towers, the needle lunged and stopped, causing the helicopter to roll and rotate in a dynamic rollover with the crosswind before crashing.
The board said the needle's stop was possibly due to its contacting the tower or to the cable catching on a ground obstacle.
As a result of the incident, Airspan suspended AS350 operations and conducted a review of its standard operation procedures and safety management system.