Malaysia Airlines flight MH370 was close to running out of fuel at the time a satellite picked up its last confirmed signal at 8.11am on March 8 - seven hours and 31 minutes after take-off.
"It must have been almost flying on fumes," a source in Kuala Lumpur with knowledge of the investigation said.
Airline officials said last week the Boeing 777 with 239 people on board had enough fuel to fly up to eight hours.
Investigators say that because of the imprecise satellite data picked up from the plane it might be anywhere in a number of countries covering thousands of square kilometres, from central Asia to Indonesia.
"The investigation team is making further calculations which will indicate how far the aircraft may have flown after this point of contact," Malaysia's Prime Minister, Najib Razak, said on Saturday.
Where a massive search effort involving 14 countries was concentrated for most of last week in the South China Sea, from where the $54 million plane vanished, planes and ships are being redirected into two possible arcs or "corridors".
A northern one stretches from northern Thailand through to the border of central Asian countries Kazakhstan and Turkmenistan and a southern one from Indonesia to the southern Indian Ocean.
The northern route could have taken the plane through countries including China, India, Pakistan and Afghanistan.
The region includes countries with unstable governments, extremist groups and remote, mountainous areas.
Flying a southern corridor would have put the plane over the Indian Ocean, a vast expanse of water with thousands of square kilometres from land mass.
How a plane 74 metres long with a 61-metre wing span could go undetected while perhaps flying through countries that are highly militarised remains unexplained.
Mr Najib revealed that investigators believe with a "high degree of certainty" that one of the plane's communications systems, the Aircraft and Communications Addressing and Reporting System (ACARS), was disabled before the plane reached the east coast of Malaysia.
Shortly after, while the plane was flying over the South China Sea and the near the border with Vietnam's air traffic control, someone on board switched off the aircraft's transponder, which communicates location and altitude to civilian air traffic controllers.
The last contact with the plane was when Kuala Lumpur air traffic control told the pilots they were heading into air traffic control based in Ho Chi Minh City in Vietnam.
"All right, good night," the pilot responded.
Shutting down ACARS and the transponder would require the specialised knowledge of one of the world's most sophisticated planes, indicating either a pilot or someone on board who had studied the plane's systems. Turning off the transponder requires someone in the cockpit turning a knob with multiple selections to the "off" position while pressing down at the same time.
Disabling the information part of ACARS system requires hitting switches to make changes seen on a computer screen in the cockpit.
But there is another part of the ACARS system, experts say, that was critically not turned off. This involves picking up the carpet and going into an electronics bay beneath the cockpit.
Investigators have reached the conclusion the plane turned in the opposite direction from its flight path and flew west, back across peninsular Malaysia, because they traced "blips" from the ACARS transmitter on satellites that were sent out once an hour after the transponder was turned off.
The blips don't contain any messages or data but the satellite can tell in a broad way what region the blips are coming from.
From the point where the transponder was turned off, Malaysian air force radar showed that an aircraft which was believed - but not confirmed - to be MH370 did turn back.
"It then flew in a westerly direction back over peninsula Malaysia before turning north-west," Mr Najib said.
"Up until the point at which it left military primary radar coverage, these movements are consistent with deliberate action by someone on the plane," he said.
Malaysia Airlines said that tracing a plane from satellite data was unprecedented for the aviation industry.
"There has never been a case in which information gleaned from satellite signals alone could potentially be used to identify the location of a missing commercial airliner," the airline said.
While dozens of planes and ships were criss-crossing the South China Sea, and while rumours and misinformation swirled around the investigation for days, the airline and Malaysian authorities kept secret the existence of the satellite data indicating the plane had turned back.
"Given the nature of the situation and its extreme sensitivity, it was critical that the raw satellite signals were verified and analysed by the relevant authorities so that their significance could be properly understood," the airline said after it had briefed relatives in Kuala Lumpur and Beijing on Saturday.
"This naturally took some time, during which we were unable to publicly confirm their existence," the airline said. "We were well aware of the ongoing media speculation during this period and its effect on the families of those on board ... their anguish and distress increases with each passing day, with each fresh rumour and with each false or misleading media report," it said.
"Our absolute priority at all times has been to support the authorities leading the multinational search for MH370 so that we can finally provide answers which the families and the wider community are waiting for."
Mr Najib also conceded authorities had not been transparent about what was known despite Malaysia's Defence Minister, Hishammuddin Hussein, repeatedly telling media briefings "we have nothing to hide".
"There has been intense speculation," Mr Najib said on Saturday. "We understand the desperate need for information on behalf of families and those watching around the world."
"But we have a responsibility to the investigation and the families to only release information that has been corroborated ... our primary motivation has always been to find the plane."
Mr Najib said the search was not called off in the South China Sea until Saturday, despite the existence of the satellite data indicating the plane had flown on for hours because it could not be confirmed.
He said he was briefed on the "new information" on Saturday morning.
The maximum range of a Boeing 777-200ER is 14,305 kilometres, prompting wild speculation about where it could be and the motivation for the disabling of the plane's communications and veering it far off its flight path.
Even hours before Mr Najib's announcement, media mogul Rupert Murdoch tweeted "maybe no crash, effectively hidden, perhaps northern Pakistan, like Bin Laden".
It is not clear exactly how much fuel the plane was carrying. It would have been enough to reach its scheduled destination Beijing, a flight of five hours and 50 minutes, plus considerable reserve for safety reasons.
Mr Najib has urged caution about describing what happened as a hijack but did not provide any other explanation.
"I wish to be very clear: we are still investigating all possibilities as to what caused MH370 to deviate from its original flight path," he said.
Mr Najib said the search for MH370 had clearly entered a new phase.
"Over the last seven days, we have followed every lead and looked into every possibility," he said. "For the families and friends of those involved, we hope this new information brings us one step closer to finding the plane."
- Fairfax Media