• Helicopter crashes in Arizona, hitting a slackline above a remote canyon
• Four members of a single family killed

Four people died after a helicopter crashed into a tensioned slackline stretched across a remote canyon in the U.S. state of Arizona, during an extreme rope-walking activity.

The Pinal County Sheriff's Office reported that the line was over one kilometer long, noting that a witness said they saw the helicopter strike part of the line before falling to the canyon floor.

The slackliners had officially notified authorities of the line’s presence through an aviation safety notice known as a "Notam," raising questions about whether the pilot had seen the warning prior to the flight.

The cause of the crash remains unconfirmed, as investigators from the National Transportation Safety Board (NTSB) and the Federal Aviation Administration (FAA) continue to examine the incident, with an official report expected within 30 days.

Slacklines are long, sturdy pieces of fabric stretched above the ground, more flexible than traditional tightropes, allowing athletes to bounce and move freely. They can be set at low or high elevations for highlining activities.

Authorities said preliminary evidence indicates the line stretched over a kilometer across the mountains near Telegraph Canyon east of Phoenix, and a witness who called 911 confirmed seeing the helicopter strike the line before it fell.

The victims were confirmed as members of a single family from Oregon: pilot David McCarty, 59, and two of his three daughters, Rachel McCarty, 23, and Faith McCarty, 21, along with Kaitlyn Heideman, 21.

The helicopter wreckage was moved to a secure facility for further examination, and authorities stated that no one was on the line at the time of the crash.

NTSB spokesperson Keith Holloway noted that aircraft collisions with wires or lines are often hard for pilots to see and confirmed that it has not yet been determined whether the slackline caused the crash.

The International Slackline Association issued a statement expressing deep sorrow, confirming that the slackliners had taken all safety measures, including attaching aviation markers for better visibility, and that the FAA had been informed and issued a notice prior to the accident.

The aviation notification system is used to alert pilots to potential hazards, such as birds or equipment near runways, though safety experts have criticized it as outdated and cumbersome.