Frederick Valentich was an Australian pilot who disappeared while on a 125-nautical-mile (232 km) training flight in a Cessna 182L light aircraft, registered VH-DSJ, over Bass Strait. On the evening of Saturday 21 October 1978, twenty-year-old Valentich informed Melbourne air traffic control that he was being accompanied by an aircraft about 1,000 feet (300 m) above him and that his engine had begun running roughly, before finally reporting: "It's not an aircraft."

Bass Strait is a strait separating the island state of Tasmania from the Australian mainland. The strait provides the most direct waterway between the Great Australian Bight and the Tasman Sea, and is also the only maritime route into the economically prominent Port Phillip Bay.