Many theories and speculation – but scant details – had emerged from the investigations, with no concrete clues to provide answers to the questions, which ranged from how a massive Boeing 777 aircraft with 239 people on board could have vanished into thin air, to why investigators think the communications system was deliberately switched off.
British daily The Guardian has attempted to answer some of these questions, as follows:
• How can a plane disappear?
Professor David Allerton of the University of Sheffield took the Malaysian authorities to task over what he claimed was a "lack of reaction on the ground".
"If this had happened in Europe or North America, within a few tens of minutes people would have worked out there was something very strange going on, and they would have done something, for example, scramble aircraft.
"If you lose communication with an aircraft, and certainly if you lose its transponder returns, you assume something quite bad has happened.
"It doesn't seem to me that the Malaysian authorities were very responsive to what was happening in their airspace. When you ask: 'How could this happen?', if the air traffic controllers haven't been monitoring things very closely then it would be seven hours before somebody realised it hadn't got there," he told The Guardian.
• Why do Malaysian officials seemingly think the plane's ACARS communications system was deliberately turned off?
It is hard to say, The Guardian said. Unlike transponders, ACARS is optional, according to Inmarsat, the satellite company on whose network it is hosted.
"Because ACARS is not mandatory for all airlines, it's therefore not universally set up in the same way," said David Coiley, Inmsarat's vice-president for aviation.
"If it was turned off it might send different messages to the ground, depending on the setup."
The intermittent signals to satellites by which investigators have determined the plane flew on for some hours, are part of the core Inmarsat system, on to which ACARS is attached. Such signals, known as "heartbeat messages", are a standby mode to check that the plane is still logged into the satellite network.
• Could the plane have lost pressure?
There are examples of planes flying for hours before running out of fuel after cabin depressurisation left the flight crew unconscious. In 2005, 121 people died when a Cypriot airliner crashed into a mountain after the crew seemingly ignored or misunderstood warnings about cabin pressure.
A gradual loss of cabin pressure can be hard to notice, said Allerton: "Military pilots are trained to detect hypoxia, but generally civilian pilots aren't. It's a very insidious thing, you might not realise at the time it's happening to you, and by the time you've realised it's too late, as you're dopey."
The fact the plane appeared to deliberately change course, with the transponder and other communications turned off, make this appear unlikely, said The Guardian.
• Why did passengers or cabin crew not make mobile calls if they realised the plane was off course?
Experts say calls can be made even at high altitude. "It is theoretically possible," Dan Warren, senior director of technology at the GSM Association, told The Guardian. "It would depend on the spectrum range you're in with your phone. It also depends on the power output of the cell itself.
"It would also depend on the landmass and network they were flying over, and the roaming agreement of the various network operators. There's not really a clear cut answer."
If a plane were to fly over the sea, he added, mobile contact would stop, but this depends on altitude and the direction.
Some planes have systems to enable passengers to make calls using a satellite link, but it is not thought to have been fitted in the Boeing 777, The Guardian said.
• What role could have been played by reinforced cockpit doors?
Since 9/11, airlines have been fitted with strengthened flight deck doors, intended to prevent intruders from taking control. If whoever took control of the plane barricaded themselves in there, not much could be done by anyone else, said Allerton to The Guardian.
"They're designed to be impregnable, so six terrorists can't kick it down. They're steel reinforced, with a solid locking mechanism. The assumption is you'd always have two or three people on the flight deck and they wouldn't all go mad."
The doors are often opened, for example, to pass food to the pilots.
Last week, photographs had also emerged showing the co-pilot of flight MH370 entertaining women in an aircraft cockpit during a previous flight. – March 18, 2014.