On October 21, 1978, twenty-year-old pilot Frederick Valentich radioed Melbourne air traffic control to report a large, shiny, unidentified object orbiting his Cessna 182 over Bass Strait. His last words were 'It's not an aircraft.' He and his aircraft were never found.

The full radio transcript is held in National Archives of Australia file series B1497, control symbol V116/783/1047, published by the Department of Transport in 1982. An RAAF P-3 Orion and eight civilian aircraft searched over 1,000 square miles without result. Around twenty eyewitnesses along the Great Ocean Road reported a green light matching Valentich's description the same evening. The Department of Transport's official finding was 'cause unknown.' An engine cowl flap matching Valentich's Cessna washed ashore on Flinders Island five years later.