The final picture: The missing jet is pictured here in February this year above Polish airspace

How can an airliner vanish from the skies?

The short answer is: very easily, if a bomb goes off. In all other circumstances, including those that appear to concern flight MH370, it takes considerable effort.

The Boeing 777-200 left Kuala Lumpur at 12.41am local time on Saturday, March 8, bound for Beijing.

At 1.19am, shortly before leaving Malaysian airspace, the co-pilot said ‘good night’ to his home country’s air traffic control.

Flight MH370’s location has been a mystery ever since.

The principal reason for the lack of information surrounding its whereabouts has been the disabling of two crucial communication systems.

The first is its transponder, a device used to send details of location, speed and altitude to air traffic control. It  was manually switched off or failed at 1.22am.

The second was its Aircraft Communications Addressing and Reporting System (ACARS), which sends data about on-board systems to the ground every half-hour.

It made a report as scheduled at 1.07am. But at 1.37am, its next report failed to materialise.

What about radar?
Malaysian air traffic control stopped following the flight after it left the country’s airspace and entered neutral territory, as protocol dictates.

Since the plane never entered Vietnamese airspace, their colleagues in Ho Chi Minh city (Saigon) never picked it up on their radar screens.

The Malaysian military, meanwhile, maintained primary radar contact with flight MH370 until 2.15am.

But because the plane had set off from Kuala Lumpur and remained initially in a major air corridor, they apparently did not realise that an  emergency was developing.

The radar systems of other nearby countries never spotted the plane.

Indian officials say their installations on the Andaman and Nicobar islands were probably switched off at the time because they ‘operate on an “as required” basis’.

That aside, any aircraft deliberately flown below 5,000ft is often able to evade radar detection.

Where could MH370 have gone after contact was lost?

Malaysia’s military radar data suggests that, after bidding farewell to air traffic control off the country’s northern coast, the jet climbed to 45,000ft, turned sharply west, then descended unevenly to 23,000ft.

It flew past the northern city of Penang before climbing again to 35,000ft. A final radar signal was detected over the Malacca Strait, to the west of Malaysia.

The low-flying theory is given more credibility by reports in the Singapore-based Straits Times that villagers near Kelantan in the isolated north-west of Malaysia saw bright lights and loud noises at the time the aircraft would have crossed over the region.

Low flying is often employed by fighter jets to use the terrain — hiding behind hills and the curvature of the Earth — to make them invisible to radar.

But those small planes are agile and strong enough for sharp turns, with radar to detect the hills. To attempt this in a large plane at night risks disaster.

Our primary source of information about the aircraft’s subsequent movements comes from a satellite owned by Inmarsat, a British firm that provides subscribing airlines with in-flight maintenance data.
It appears to have picked up hourly ‘pings’ from flight MH370 until 8.15am.

But they only reveal the rough distance the aircraft was from the satellite, rather than its exact location.

Investigators therefore believe the flight ended up in one of two ‘air corridors’. The first runs from the southern border of Kazakhstan to Laos and northern Thailand.

The second begins in Jakarta and ends in the ocean 1,000 miles off Australia’s west coast.

Is there evidence it crashed?
Oil worker Mike McKay, a New Zealander working on a drilling platform in the South China Sea, has said he believes he saw an aircraft on fire at around the time MH370 disappeared.

Yet despite a ten-day search, involving 43 ships and 58 aircraft from 15 nations, in a busy and comparatively shallow patch of water, no trace of wreckage has been found.

This is highly unusual, since aviation fuel slicks and other debris tend to make maritime crash sites highly visible.

For example, fragments of Air France flight 447, which went missing off the coast of Brazil five years ago, were quickly discovered on the ocean surface (though locating the actual plane took some time).

Most experts therefore believe that if a crash actually did occur, the most credible location for it to have happened was in the more remote, and still only partially searched, southern air corridor.

Was there a black box?
All commercial flights carry a flight data recorder, which is, in fact, painted bright orange and carries exhaustive data that can usually reveal the fate of a crashed plane.

The tricky bit is locating it.

After an incident, the devices emit a signal beacon to help investigators find them. But their range is only 2,000 to 3,000 metres — and much less if they are in deep water, as this one may be.

How likely is hijacking?
Since 9/11, locked security doors have protected the cockpits of all commercial passenger jets during flights.

While a hijacker could potentially break down such a door, perhaps using the hidden fire axe, it seems highly unlikely that they could do so without authorities on the ground being quickly alerted.

Emergency protocol dictates that the moment the attack commences, the pilot immediately changes the code on the transponder to 7500, a form of instant ‘mayday’ call.

In this case, that clearly did not happen. In addition, unless the passengers are instantly incapacitated, they might use mobile phones to call or text their families in an emergency.

But there is no evidence that any of the 239 people on board MH370 did any such thing.

Why are the pilot and co-pilot being investigated?
The absence of any emergency call  suggests that any hijacking would most likely be ‘air piracy’ — an inside job, involving the pilot or co-pilot, along with members of the crew.

The two men, Zaharie Ahmad Shah, 53, and 27-year-old Fariq Abdul Hamid, are therefore the focus of investigations.

Could either man have been a potential hijacker?
Shah, a married father-of-three, is an activist for Malaysia’s pro-democracy People’s Justice Party.

The day before the flight disappeared, he attended the trial of Anwar Ibrahim, an opposition leader jailed for five years on what many believe to have been a trumped-up charge of sodomy.

Last May, Shah was photographed wearing a T-shirt saying ‘democracy is dead’.

The picture was taken at stadium where 50,000 protested against the result of a recent election they believed to be fraudulent.

Police who searched his gated pink house in Kuala Lumpur took away a six-screen flight simulator similar to the device the perpetrators of the 9/11 attacks trained on.

Hamid, meanwhile, is a bachelor who lives with his parents and a regular at his local mosque.

His fiancee has been identified as Captain Nadira Ramli, 26, who flies for Malaysia-based budget carrier AirAsia — Malaysia Airlines’ fierce rival — and is the daughter of a senior Malaysia Airlines pilot.

There will be renewed interest in Hamid after it emerged it was he, not Shah, who spoke the last words to air traffic control, suggesting he  could have been in control of the  aircraft at that point and perhaps subsequently.

Could the aircraft have landed safely?
A Boeing 777-200 can be landed anywhere there is 2,000 to 3,000 straight metres of relatively flat tarmac.

Flight MH370 had enough fuel to travel about 3,000 miles from its last known position over the Gulf of Thailand.

There are approximately 634 suitable runways within that radius.

In extremis, the plane could also  be landed on any empty wide road or on one of the hundreds of old air-strips still to be found in remote regions of Vietnam, Laos and Cambodia.

There is, therefore, no shortage of potential landing sites.

‘Given the absence of crash wreckage or any maritime oil slick, I prefer the “safe landing” explanation to the others out there,’ says aviation expert Julian Bray.

Such a scenario would only have come about, Bray says, if the flight evaded radar defences (most likely by flying at a few hundred metres).

After landing, the perpetrators would then have had to keep the 73m long plane and its passengers hidden once it was on the ground.

Where does the search go from here?
The absence of evidence of a crash raises the prospect of a hijacking or act of ‘air piracy’, in which hostages could be traded for financial reward  or political concessions.

The flaw in that argument, of course, is that if the plane was being held somewhere, after ten days it is likely whoever ‘stole’ it would have broken cover to make demands — unless of course they are already negotiating with a secretive regime such as China or Kazakhstan.

In the case of straight terrorism, the group that perpetrated it will also have to claim responsibility in order for it to exact any political leverage from the attack.

In the meantime, investigators believe that they will eventually be able to sift through the satellite data to establish the exact path the flight took.

However, the process will be hugely painstaking, due to the sheer volume of data that the investigators will be faced with.

‘It’s like a mobile network trying to trace a mobile phone that didn’t have an account set up and which was turned off at the time,’ says aviation expert David Learmount.

In other words, the truth is out there, but it could be a long time coming.