Nepal air crash: Aviation expert's theory on what caused plane to plunge from ... trends now

The thin atmosphere of a high altitude runway and an optical illusion may have led to Sunday's air crash in Nepal which killed 68, with the fate of one Australian on board still unknown.

Aviation expert Professor Ron Bartsch said the Yeti Airlines' ATR 72 ploughed into the ground after it appeared to suffer a mid-air stall as it tried to land.

The plane was on final approach at Pokhara, on the edge of the Himalayas 200km west of capital Kathmandu.

Video captured its final chilling moments just as it came in to land after a 25 minute flight to the city's new airport, 822m above sea level.

Life in the central resort of Pokhara has ground to a standstill after the shocking crash earlier today

It suddenly banked left and plummeted from the sky with 72 people on board, in the nation's worst air disaster in three decades.

Prof Bartsch believes the pilot may have lost control after an optical illusion made him think he was travelling faster than he was, causing the plane to stall.

Aircraft need to fly at faster speeds through the thinner air at higher altitudes to stay airborne - and the high altitude runways of Nepal are notoriously tricky to navigate.

'The runways are very, very challenging, some of the most challenging in the world,' he told Nine's Today show on Monday.

Aviation expert Professor Ron Bartsch (pictured) says the Yeti Airlines' ATR 72 ploughed into the ground after it appeared to suffer a mid-air stall as it tried to land

'That terrain is terribly difficult to fly - very strong winds and high altitude. Normally aircraft don't just fall out of the sky, particularly modern aircraft.'

He ruled out any chance of mechanical failure and instead suspected the pilot had stalled the twin-engined prop plane in the tricky conditions and thin air.

'Aircraft require air to fly in and the air is more rarefied at about 800 meters elevation there,' he said.

'But also the fact when you're going over the ground, it may appear that you're going a lot faster over the ground than what you're going through the air.

'I'd suggest that the aircraft has entered into an aerodynamic stall...that's what caused this.'

Footage appears to show the plane flying over houses in the town in the central region of Nepal

NEPAL'S TROUBLED AIR CRASH HISTORY

Nepal's air industry has boomed in recent years, carrying goods and people between hard-to-reach areas as well as foreign trekkers and climbers.

But it has been plagued by poor safety due to insufficient training and maintenance.

The European Union has banned all Nepali carriers from its airspace over safety concerns.

The Himalayan country also has some of the world's most remote and tricky runways, flanked by snow-capped peaks with approaches that pose a challenge even for accomplished pilots.

Air accidents are not uncommon in Nepal, home to eight of the world's 14 highest mountains, including Everest, as the weather can change suddenly and make for hazardous conditions.

Aircraft operators have said Nepal lacks infrastructure for accurate weather forecasts, especially in remote areas with challenging mountainous terrain where deadly crashes have taken place in the past.

The weather can also change quickly in the mountains, creating treacherous flying conditions.

Airport officials have confirmed an Australian was among the 15 foreign nationals on board the domestic flight from Kathmandu, along with five Indians, four Russians, one Irish national, two South Koreans, one French national and an Argentinian.

It's currently unknown whether the Australian was killed or is one of the four survivors of the horrific crash. Daily Mail Australia has contacted Department of Foreign Affairs and Trade for more details.

The harrowing video clip of the crash showed the plane making a sharp turn before plummeting to the ground seconds later with a