The missing Malaysia Airlines passenger jet was more likely to have travelled along a southern course near Australia and should have been picked up by that country's radar network if it did so, a leading surveillance analyst says.
Investigators have identified two possible corridors for flight MH370 after it emerged its transponders were deliberately turned off and satellite data showed it flew for almost seven hours after veering off course in the Gulf of Thailand.
The southern arc took MH370 over Indonesia and down the Western Australian coast, about 1000km from land.
The northern trajectory goes towards northern Iran, passing through Pakistan and Afghanistan, the heartland of Al Qaeda and multiple Islamic extremist insurgencies.
While the route goes over countries renowned for security instability, the region is covered by multiple radar systems.
"It's hard to believe it could go over northern Thailand undetected. They have extensive radar," said Des Ball, professor of strategic and defence studies at the Australian National University.
There are also radar installations operated by Myanmar, China, India and the US, among others, underneath the northern flight path. In addition, high tech US surveillance satellites also intently monitor the area as part of the war on terror.
"Going over land is more logical but it's hard to see how the plane wouldn't have been detected," said Ball.
Even though MH370 turned off its transponders and disabled its secondary radar, military radar and some civilian radar would be able to pick it up with what is known as primary radar.
Malaysia's military radar, for example, identified the plane as it tracked west across Malaysia in the early hours of March 8 but failed to act.
Australia has one AP-3C Orion surveillance plane scouring the sea near the Cocos Islands, while the other is operating west of Malaysia, chief of the defence force General David Hurley said.
But Defence declined to confirm whether its radar and surveillance assets were also being deployed to help the search for the missing plane, which vanished over the Gulf of Thailand with 239 people on March 8.
Ball said the reach of Australia's powerful Jindalee radar system over-the-horizon radar is 3000km and could be expected to have picked up the Boeing 777 jet as it traversed Indonesia on any southern route.
However, whether Jindalee, which targets beyond northern Australia, could precisely identify the plane is another matter, as it would have appeared as "just a dot on the screen", said Ball.
Ball said that MH370 data received by the satellite hovering over the Indian Ocean was basic, little more than a ping that could only be used to identify the two possible routes, the mirror image of each other in a 180 degree arc.
The last transmission came at 8.11am local time on March 8, when the plane would be about to run out of fuel.
- Sydney Morning Herald