Today in History - October 21: 'It's not an aircraft': Final words of pilot after spotting mystery object

In one of Australia's greatest aviation mysteries, a young pilot and his light aircraft vanished off the Tasmanian coast on October 21, 1978.

Frederick Valentich, 20, a keen pilot and a member of the RAAF air training corps, was flying a Cessna 181 plane from Melbourne to King Island during the evening when he reported a strange aircraft.

Valentich radioed to air traffic control the object had bright lights and had flew close to him a number of times at great speed.

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He said It was orbiting about 300m over his plane and described it as having a green light with a shiny surface.

Valentich thought it may have been a military plane and requested confirmation as he flew over the Bass Strait.

Then it suddenly vanished.

Valentich confirmed to air controllers he was continuing his flight to King Island, where he intended to collect crayfish.

But moments later, he reported the strange object was back, saying "it's not an aircraft".

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They were the last words from Valentich as all radio contact with him was lost.

The young pilot and his single-engine plane were never seen again.

The disappearance triggered a major sea and air search over a 2600 square kilometre area. The RAAF deployed an advanced P-3 Orion reconnaissance plane as part of the efforts, but the search found nothing.

Valentich's mysterious disappearance made headlines in Australia and across the world.

The theory that a UFO was behind it gathered momentum after authorities received hundreds of reports of unknown shining objects in the sky across Victoria on the night Valentich disappeared.

Aviation safety officials also discovered Valentich was a keen UFO enthusiast, and he hadn't told King Island airport he intended to land there.

This fuelled theories he was planning his own mysterious disappearance, or was going to take his own life.

But family and friends of Valentich insisted he was a mature and well-adjusted young man.

In 1982, a coronial inquiry into the case found an open verdict, finding Valentich was missing, presumed dead.

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