South-east Asia is busy in aviation terms, but air-traffic management is not as effective as in Europe. The main way to detect an aircraft whose transponder is turned off is through "primary radar". This is Second World War technology that sweeps the sky with a high-energy electromagnetic beam and registers reflections. An unexplained radar "blip" in the early hours of the morning may go unnoticed, especially if it goes away quickly, or may not prompt a reaction.
Video: Jet search expands with few clues
Q | I don't understand from the "pings" why the aircraft can be in two possible corridors in relation to the satellite?
A | After the main communication systems were turned off aboard MH370, one channel remained open: a periodic "handshake" between the aircraft and an Inmarsat communications satellite in geo-stationary orbit 22,250 miles above the Indian Ocean. The last was at 8.11am, local time. From the time that it took the responding "ping" to reach the satellite, it is possible to compute the distance from the satellite. Then, elementary geometry comes into play: draw a circle on the surface of the earth showing all the points that match that distance. The circle has a circumference of about 18,000 miles, but most of it can be disregarded because of the limited range of the plane from its last known point. The aircraft is unlikely to be exactly on one or other arc, since in the time since that handshake was registered it could have flown 250 miles in any direction.
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Q | Do cabin crew have no way to signal an "incident"? Perhaps they should.
A |Cabin crew have access to emergency locator transmitters, but these are electronic distress beacons designed to be used in the event of a ditching at sea or forced landing, rather than in flight. There is no publicly available evidence that one was activated aboard MH370.
Q | What will the impact be on airline security?
A | The long-term effects will depend upon what more we learn. But already the aviation community is looking at two possible areas of intensified security. The revelation that two passengers were travelling on stolen passports may lead to a requirement that details of travel documents are checked against a central database of missing passports. And if it is found that either an intruder to the flight deck or one of the pilots was responsible for the disappearance, there may be calls for an air marshal to be seated in the cockpit to deter unwanted intrusions and keep an eye on the captain and first officer.
Q | Weren't there reports of passengers' mobiles still ringing?
A | Some reports suggested that passengers mobiles were ringing rather than going straight to voicemail - but it seems this was due to the phone networks configuration. One of the most troubling aspects of this case is the absence of reliable evidence of contact between people on the plane and their relatives on the ground. If and when the passengers became aware of a threat, a natural response would be to attempt to contact family. Although calls from 30,000ft do not usually work, SMS messages sometimes do. In their absence, it is difficult to conclude other than that the passengers were prevented from using them, or that the plane was flying well out of range of mobile-phone masts.
- THE INDEPENDENT
