ADELAIDE - Adelaide adventurer Duncan Chessell is on the brink of becoming the first Australian to climb Mt Everest three times, an endeavour which he believes may prove Sir Edmund Hillary and Sherpa Tenzing Norgay were not the first to reach the summit.

Chessell has reached 7700 metres on the mountain along with his team and plans to strike out for the 8848m peak within 24 hours.

If successful it will follow his other trips to the top of the world in 2001 and 2007.

On the descent he also plans to try to solve the greatest mystery in mountaineering - who was the first to reach the Everest summit.

While Sir Edmund and Norgay are credited with being the first to the top on May 29, 1953, some think two English climbers beat them there by almost 30 years.

George Mallory and Andrew Irvine may have reached the summit in June, 1924, but died on the way down.

The pair was last seen on the ascent, just a few hundred metres from their goal.

Mallory's body was found in 1999 but certain pieces of equipment, including cameras, and personal effects were not located.

The body of Irvine has never been found.

Chessell thinks he knows the likely site where Irvine's body would now lie and believes conditions for a search on the mountain this year are the best in decades.

He thinks Irvine may have survived a fall but died on his way down while taking a route not often used.

"We know he did not return to high camp - so he perished between the first step and high camp," Chessell said on Monday.

"If Irvine used the normal climbing route he would have been found.

"We will concentrate our efforts on the alternative descent route where I think he succumbed to his injuries."

Chessell said his team's time in the death zone (above 8000m) would be limited to just a few hours but he remained confident of success.

If they can find Irvine's body, and more importantly the missing cameras, it may solve the mystery of who reached the summit first.