Confirmation that a missing Malaysian airliner was deliberately diverted suggests several scenarios that will sharpen scrutiny of the cockpit crew and passengers known to have boarded with stolen passports.
Prime Minister Najib Razak yesterday announced that satellite and radar data clearly indicated the plane's automated communications had been disabled and the plane then turned away from its intended path and flown on for hours.
Since the September 11, 2001 terror attacks, the International Civil Airline Organisation has mandated high security standards for plane cockpits. Cockpit doors -- reinforced to withstand bullets -- must be locked from the inside before push off from the gate.
"So for me there's only a few scenarios," said Paul Yap, an aviation lecturer at Temasek Polytechnic in Singapore.
"First the people involved in the deliberate actions are the pilots, one of them or both of them in cahoots. Then we have a scenario where terrorists make the pilots change course and switch off the transponders under duress, maybe threatening to kill passengers," Yap said.
The transponder of MH370 was switched off around the time analysts said it would have reached its cruising altitude, when pilots often emerge to take a bathroom or coffee break.
While other theories are still being examined, the US official said key evidence suggesting human intervention is that contact with the Boeing 777's transponder stopped about a dozen minutes before a messaging system on the jet quit. Such a gap would be unlikely in the case of an in-flight catastrophe.
The Malaysian official said only a skilled aviator could navigate the plane the way it was flown after its last confirmed location over the South China Sea. The official said it had been established with a "more than 50 per cent" degree of certainty that military radar had picked up the missing plane after it dropped off civilian radar.
Why anyone would want to do this is unclear. Malaysian authorities and others are investigating the backgrounds of the two pilots and 10 crew members, as well the 227 passengers on board.
If hijackers are suspected, then the glare of suspicion will fall again on two Iranian passengers who boarded with stolen EU passports.
London-based David Kaminski-Morrow, air transport editor for Flight International, warned of the danger of rushing to conclusions following Najib's announcement.
"The new evidence is consistent with deliberate action, but it's still only a small amount of data -- certainly not a complete picture -- and therefore it's still premature to label the event formally as a hijack," Kaminski-Morrow said.