How investigators figured where MH370 can possibly be

That something as big as a Boeing 777-200ER aircraft can vanish suddenly has baffled aviation specialists and air crash experts. Or that it could possibly be thousands of kilometres away from its original flight path.

Satellite communications are behind the latest revelation that Malaysia Airlines flight MH370, missing since March 8, could have flown for seven more hours and ended up thousands of kilometres away from its original destination without being detected by ground radar.

Malaysian authorities disclosed that satellites picked up faint electronic pulses from the passenger jet after it went missing from radar systems, but the signals or "pings" gave no information about where the stray jet was heading and little else about its fate.

A “ping” is an indication that the aircraft’s maintenance troubleshooting systems are ready to communicate with satellites.

Tim Farrar, a satellite communications consultant, who founded California-based technology consultancy firm Telecom, Media and Finance Associates, has offered a simplified account to understand ow satellite pings in a blog post.

He said an aircraft has two types of contact that was last sighted – a radar transponder and a satellite ping – but both are not linked to the other.

He compared the radar transponder with the plane's “Bluetooth”.

The military radar transponder should be able to locate the plane the same way a bat navigates by echolocation – it sends out an amplified signal that will reflect off the metal of the plane and returns with additional information such as the plane's identification.

Radar should be able to pick up on the location of any vessel with a transponder, especially military radars which are much more sensitive than civilian radars, he said.

"If turned off, less sensitive civilian radar will struggle to pick up the plane’s reflection, though military (air defence) radar should still be able to see the plane.

"But military radar systems are looking for hostile forces and have missed civilian aircraft in the past," said Farrar in his company's blog.

The second point of contact, said Farrar, was the satellite ping, which became an active terminal in the eyes of the global satellite network, Inmarsat, when a plane was ready to take off. Inmarsat sends “requests” at intervals to the aircraft, in order to keep confirming it is active.

Farrar illustrated how this works by relating it to mobile phone networks.

"Sometimes when you go on a trip and the location is new to you and your mobile service provider, it will tell you that you have 'No Network Connection'.

"The mobile phone company knows this because it has been constantly requesting the phone to confirm its activity, and once the phone leaves its familiar connection, the phone company immediately tries to find data it can connect to in order to make sure the phone knows what to do with an incoming call," he said.

Inadvertently, this will place one's rough location to your mobile service provider as well. This was the same with the aircraft that went missing, he added.

"Similarly with Inmarsat, there isn’t a need to know exactly where in a cell the plane is located, just that it’s there and not somewhere (or nowhere) else," said Farrar.

Even with its transponders turned off, a plane could still be connected to the Inmarsat network which received affirmative “pings” from the aircraft terminal that it was still active.

Farrar then brought out the big question: can the Inmarsat network accurately show where the plane was located?

According to him, the terminal which MH370 had onboard seemed to be a Swift64, which he said is not among the latest SwiftBroadband terminals which had yet to be approved for aeronautical safety services.

The Swift64 uses a global beam to maintain network registration and receive “pings” and this makes it harder to rule out locations compared with if it was using regional beams.

Accuracy was already compromised through the global beam, said Farrar, but looking at the position it was in, there were two potential ways to measure its location on that vast global beam.

The first is to look at the time delay of transmission from signal to satellite, which will determine a range from the sub-satellite point that will narrow down a circle on the Earth's surface.

The second is to measure the power level of the signal received by the satellite.

"If you know the transmission power accurately enough and know how much power was received, you can estimate the angle it came from. This again would produce a similar range from the sub-satellite point, expressed as a circle on the Earth’s surface.

"We can see that the search locations are based on exactly these curves at a given distance from the sub-satellite point.

However, it is unlikely that the measurements are more accurate than within say 160km," he added.

Referring to the new search area for MH370 as announced yesterday, Farrar pointed to the two arcs cut off on the east and north boundaries.

He said the two arcs are possible boundaries established due to the transmission that was received by Inmarsat’s Pacific Ocean Region satellite at that point, or speculation on the amount of available fuel, not satellite measurement of range.

It was announced yesterday that search for the missing plane was now on two air corridors the plane was believed to have taken.

One was the northern corridor of the Indian Ocean – Andaman Sea, Bay of Bengal and overland right up to the southern tip of Kazakhstan and the other the southern part of the ocean, where there is little land mass. – March 16, 2014.