ONE week after the passengers on Malaysia Airlines flight MH370 began boarding at Kuala Lumpur, the first significant leads have emerged.
Evidence from satellite "pings" reveals that the Boeing 777 flew for up to five hours after all other contact was lost with the jet.
Yet many uncertainties remain, and theories to explain the disappearance of a routine flight to Beijing have multiplied to fill a vacuum of ignorance.
The known facts are sparse. Shortly after midnight local time last Saturday, 221 passengers and 12 crew departed Kuala Lumpur for the overnight journey to Beijing.
At 2.40am communication was lost with the aircraft. At the time, the jet was over the South China Sea between Malaysia and Vietnam.
Malaysia Airlines reported the disappearance nearly five hours later, an hour after the plane was due to land in Beijing.
The question of what happened to the jet has haunted the relatives of passengers - and the wider aviation community - ever since.
The jet's high-frequency radio fell silent, and the transponder stopped responding to radar interrogation.
The spectrum of possibilities to explain the sudden loss of communication was wide.
The cause could have been wholly accidental, for example a catastrophic failure of the airframe or hazardous cargo.
A technical problem might have been exacerbated by pilot error, as happened with the crash of Air France 447 between Rio and Paris in 2009.
A bomb may have exploded on board, as with Pan Am 103. Or de-pressurisation could have incapacitated the crew.
But the revelation that the aircraft remained aloft on a different heading suggests that a pilot, or someone else who knew how to fly it, was at the controls.
While the search for wreckage continues, travellers are starting to question practices in international aviation - and asking how, given 21st-century communication technology, a large passenger jet can simply vanish.
Since every iPad and iPhone owner can get an app that allows them to trace their device if lost, it seems absurd that a £160m, 250-ton jet aircraft should be untraceable.
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