In a potentially unprecedented accident, a helicopter crashed this weekend after flying into a slackline in Arizona, resulting in the deaths of all four people on board.

　　On Jan. 2, emergency services received reports of a helicopter crash in Telegraph Canyon, a popular hiking and OHV area, according to a statement from the Pinal County Sheriffs Office. First responders to the scene confirmed four deaths from the helicopter crash. No one was on the slackline at the moment of the accident.

　　An eyewitness who called 911 reported seeing the helicopter strike a portion of the line before falling to the bottom of the canyon, the sheriffs office stated.

　　The fatalities include 59-year-old David McCarty, who was flying the helicopter, and his three nieces: Rachel McCarty, 23, Faith McCarty, 21, and Katelyn Heideman, 21, the Arizona Republic reported.

　　David McCarty owned Columbia Basin Helicopters, a professional helicopter company located in Oregon, according to Oregon Public Broadcasting.

　　What Is Slacklining? Slacklining involves balancing across a flexible piece of nylon webbing strung up between two fixed points. Its risen in popularity in recent years. Many people set up slacklines between trees in parks a few feet off the ground.

　　(Photo/Jason Spafford) When slacklining is done at significant heights, its called highlining. Many people set up tall slacklines in scenic outdoor areas, such as Moab or Lake Tahoe.

　　These athletes wear harnesses and tethers in case of falling. Since 1983, 11 people have died highlining, mainly due to errors setting up their equipment, according to the International Slackline Association.

　　An Ongoing Investigation A preliminary search showed that a slackline more than 1 kmo long had been strung up in Arizonas Telegraph Canyon, about 600 feet above sea level.

　　Before the accident, the Federal Aviation Administration (FAA) had issued a Notice to Air Missions (NOTAM) to pilots, informing them of the slackline, which had aviation markers attached. The FAA and National Transportation Safety Board (NTSB) are currently investigating the incident. 

　　Within 30 days, the NTSB must release an initial report, although it can take up to 2 years for the agency to issue a final report. In general, accidents involving slacklines are extremely rare.

　　This is potentially the first aircraft accident caused by a slackline. The International Slackline Association, which tracks deaths related to slacklining, does not have any such examples listed in its online database. Most of the deaths involve those actually slacklining. In one exception from 2013, however, a cyclist was killed after riding into a slackline, according to the association.

　　GearJunkie reached out to the association for more details, but didnt hear back as of this writing.

　　The International Slackline Association released a statement on the accident. No highliners were on the line at the moment of the incident. We extend our deepest sympathy and condolences to all of those affected by this tragic event, it said.

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