KUALA LUMPUR - The dramatic expansion of the search for a missing Malaysian airliner suggests the plane flew thousands of miles off course, crossing - apparently undetected - a sensitive region bristling with military radar.
Aviation experts on Friday queried the plausibility of such a scenario, but confirmation from US and Malaysian officials that the search was being widened into the vast Indian Ocean suggested it had credible underpinnings.
If there was debate over what might have happened to Flight MH370, there was a general consensus as to the extraordinary nature of its disappearance without trace a week ago over the South China Sea.
"I would probably go ahead and say this is unprecedented," said Anthony Brickhouse, a member of the International Society of Air Safety Investigators.
"In most investigations each day you move forward, you uncover more things, more clues," Brickhouse told AFP.
"But in this one it seems that each day that goes by something that you thought was a lead turns out not to be a lead and you're back to square one again."
The expansion of the search area came as multiple US media reports, citing American officials, said the plane's communication system continued to "ping" a satellite for up to four hours after it disappeared en route from Kuala Lumpur to Beijing.
The reports amplified on Malaysia's belief, based on a radar sighting, that the plane may have mysteriously turned back towards Kuala Lumpur just over an hour into its flight when no technical problem was apparent, on a calm night in fine weather.