How flight MH370's path was confirmed

Last updated 12:39 25/03/2014
Fairfax Australia

Satellite company re-examines hourly pings sent by the missing Malaysian Airlines flight to work out its path.

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Just how did the British firm behind the confirmation of flight MH370's final path solve the mystery?

Inmarsat's engineers began searching for any trace of the plane immediately after its disappearance.

While it was quickly confirmed MH370's normal reporting system was switched off, one of the company's satellites picked up hourly "pings" from a port on the plane.

It then used these to piece together possible flight routes. The company deduced the plane continued to fly for at least five hours after leaving Malaysian airspace.

Space engineers compared the satellite handshake "pings" from missing jet MH370 with other tracked commercial flights to determine it had crashed into the middle of the Indian Ocean.

Malaysian Prime Minister Najiv Razak today (NZT) revealed that analysis "never before used in an investigation of this sort" had shown the Malaysian airliner had crashed into the southern Indian Ocean.

That analysis was undertaken by mobile communications company Inmarsat, which provides satellite data for Malaysia Airlines.

Even though the plane's transponder and ACARS system were turned off, the company's box on the Boeing 777 - equivalent to a mobile phone handset - stayed on and was polled every hour by Inmarsat's satellite.

The British company initially looked at the amount of time these handshake pings took to travel from the plane to its satellite 35,000 kilometres above the equator to determine the aircraft was moving along either a north or south corridor.

It passed on that discovery on March 11.

"Effectually we looked at the Doppler effect, which is the change in frequency, due to the movement of a satellite in its orbit. What that then gave us was a predicted path for the northerly route and a predicted path the southerly route," Chris McLaughlin, senior vice president of external affairs at Inmarsat, told the Daily Telegraph.

"They've tested it off against a number of other aircraft known flights and come to the conclusion that only the southern route was possible,"  McLaughlin told Sky News on Monday (local time).

"We refined that with the signals we got from other (777) aircraft and that then gives you a very, very good fit.

"Previous aircraft provided a pattern and that pattern to the south is virtually what we got in our suggested estimates.

"So the fit is very, very strong."

McLaughlin said the company was relying on a 1990s satellite over the Indian Ocean that wasn't GPS equipped.

But scientists could work out the approximate direction of travel "plus or minus 100 miles to a track line".

"All we can do is to say we believe it is in this general location.

"We can not give you the final few feet and inches of where it landed. It's just not that sort of system."

While the company was able to work out where the last ping was sent from, the aircraft likely still had some fuel remaining.

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But it would have run out before the next automated handshake.

Inmarsat has been appointed a technical advisor to the UK Air Accident Investigation Branch.

It passed on the new analysis after it was peer-reviewed by other experts in the UK space industry and compared with Boeing.

McLaughlin said systems that kept track of a plane's precise location should be mandated world-wide "and it could be delivered tomorrow".

- AAP, Stuff

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