Reference

The Vickers Viscount 720 crash circumstances were primarily due to structural failure. The starboard outer wing failed in upward bending due to tensile overloading of the lower spar boom, which led to the aircraft breaking up in mid-air. This was a result of faulty repair work done in 1964 where engineers "butchered" pre-drilled holes in a metal plate during an upgrade to the wing. The aircraft was not designed to withstand such stress, and the maintenance error caused the accident. The investigation by the Australian Department of Civil Aviation and British Aircraft Corporation concluded that this mysterious action during maintenance was the cause. The crash occurred on November 30, 1961, and all four crew members不幸遇难. This information is corroborated by various sources including the Aviation Safety Network, the Australian Transport Safety Bureau, and Airline Ratings.