Since the Sept 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.
The hijackers of the four planes used in the 9/11 attacks turned off the transponders of three of the jets.
Since the Sept 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.
The hijackers of the four planes used in the 9/11 attacks turned off the transponders of three of the jets.