© Sovannara/RexAround 100 people including Buddhist monks light incense sticks and candles during a prayer service in Cambodia for the missing Malaysia Airlines flight MH370.
1. Why did no passengers or cabin crew 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," said Dan Warren, senior director of technology at the GSM Association. "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 soon stop: "It wouldn't take very long to lose any kind of phone signal. It would depend on altitude and the direction you were flying in."
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.
2. What role could have been played by reinforced cockpit doors?
Since 9/11 airliners 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 would be little others on the plane could do, said Professor David Allerton of the University of Sheffield. "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 emerged of the co-pilot of flight MH370 entertaining teenage tourists in an aircraft cockpit during a previous flight.
3. Why do Malaysian officials seemingly think the plane's Acars communications system was deliberately turned off?
It is hard to say. Unlike transponders Acars is optional, according to Inmarsat, the satellite company on whose network it is hosted. "Because Acars is not mandatory for all airliners 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 the plane is still logged into the satellite network.
4. 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.
5. How can a plane disappear?
Allerton said the main issue appeared to have been the 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."
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