The latest revelation that MH370 flew right across Malaysian airspace without being challenged has turned the spotlight on airspace security in the region.

Given the plane's fuel load and last known direction, it could have headed north along a route that could have entered the airspaces of countries including Thailand, Myanmar, Bangladesh, Nepal and the central Asian republics of Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan. Or it could have flown south, through the Indian Ocean's mostly open waters.

We look at these countries' airspaces and whether it is difficult to fly through them undetected.

1. The Boeing 777's transponder was switched off, which means Air Traffic Control radars in these countries may not have registered the passage of flight MH370. But what about the military radars of these countries?

If the plane had headed north-west, it would have encountered heavily militarised areas in China, India or Pakistan. These areas would likely have closely scrutinised radar systems that would make an unauthorised flight into their airspace difficult.

However, a BBC report also pointed out that there have been reports that military radars at India's far-flung Andaman and Nicobar islands were not switched on as the threat levels there were perceived as low.

2. How did the plane manage to fly over Malaysian and other countries' airspace without triggering alarms?

A BBC report quoted a former Royal Air Force pilot and aerospace analyst Andrew Brookes as saying that this incident indicates "apparent gaps in wide area surveillance of their airspace". The report also pointed out: "It is also one thing to invest in capabilities, but another to have the training, procedures and resources to use them effectively."

3. What is the procedure for an aircraft entering a country's airspace?

Commercial air traffic usually travels designated flight paths that follow preset altitudes and corridor widths as well as fixed coodinates from satellite navigation systems and ground-based navigational aids.

Such traffic is monitored by Air Route Traffic Control Centres, which are civilian airspace authorities, in various countries.

According to a pilot The Straits Times spoke to, commercial flights usually file their flight plans, which can span several countries' airspace, three hours before taking off.

Some countries will simply hand over a plane to a neighbouring country's air traffic control centre, but some countries (such as Afghanistan and Pakistan) require that an approaching plane contact its air traffic controllers 10 minutes before entering its airspace.

4. What is the procedure if a country's military radar detects an unidentified plane?

According to the BBC report, in more developed airspace environments such as North America and Europe, civilian and military air traffic controllers would be in close contact with each other to ensure that no unauthorised aircraft can enter their airspace.

The report also laid out the procedure for air traffic controllers if they encounter an unidentified aircraft.

If military radar operators see an unidentified plane, they would check with their civilian counterparts to see if the latter can identify the transponder.

If civilian air traffic controllers cannot identify the plane, the next step is to attempt to contact the pilot by radio. If there is no response from the pilot, fighter jets would be scrambled to intercept.

5. Are radar surveillance systems foolproof?

No. As mentioned before, the systems are only as good as the operators. Radar systems also have a hard time tracking aircraft flying at low levels.

Even the most sophisticated systems have been bamboozled before. The BBC report cited the example of amateur German pilot Mathias Rust, who flew his light aircraft right into the heart of the Soviet military complex and landed his plane in Red Square in Moscow in 1987.

Radar systems can also be fooled. Aviation reporter David Cenciotti, who contributes to aviation industry publications, speculated on his website The Aviationist that one way MH370 might have evaded radar surveillance was if the Boeing 777 "shadowed" another plane.

He wrote: "Closing on another liner is not a common procedure, nor is it easy to perform with a large plane. But it is not completely impossible and, above all, such a daredevil manoeuvre worth an action movie, would have made the MH370 invisible to military radars."