MH370: seven satellite pings reveal fate
British satellite company Inmarsat analyses seven, hourly pings sent by the missing Malaysian Airlines flight to determine its final resting place.PT0M0S 620 349
London: A new satellite tracking technique is what gave Malaysian Prime Minister Najib Razak enough confidence to announce that Malaysia Airlines flight MH370 went down in the remote south of the Indian Ocean.
British firm Inmarsat was behind an earlier analysis that indicated the plane had been flying in one of two big ‘corridors’, one in the northern hemisphere and one in the southern.
Graphic: Jamie Brown
However last week it went back to its data and tried a new mathematical analysis, which concluded on Sunday.
The new analysis allowed them to discard the northern corridor, and focus more precisely on the southern route.
Based on this new information, Mr Najib announced on Monday that MH370’s last known position was in the middle of the Indian Ocean, west of Perth.
UK firm Inmarsat was behind an earlier analysis of the path of missing flight MH370. Photo: Fairfax
The nature of the pings indicated that the plane was still moving during that time.
“This is a remote location far from any possible landing sites,” he said. “It is therefore with deep sadness and regret that I must inform you that … flight MH370 ended in the southern Indian Ocean.”
The aeroplane had Inmarsat’s ‘Classic Aero’ satellite system, which collects information such as location, altitude, heading and speed, and sends it through Inmarsat’s satellites into their network.
This ‘ACARS’ (aircraft communications addressing and reporting system) was switched off or interrupted early in the flight, meaning no such information was available to track the plane.
However the Classic Aero system still sent hourly ‘pings’ back to Inmarsat’s satellite for at least five hours after the aircraft left Malaysian airspace, the company discovered.
These pings contained no data – they were just a simple ‘hello’ to keep the link open – however their timing and frequency contained hidden mathematical clues.
The company looked at the ‘Doppler effect’ – tiny changes in the frequency of the ping signal, caused by the relative movement of the satellite and the plane (the Doppler effect is the reason why, for example, police sirens are a different pitch or frequency depending on whether they are travelling toward you or away from you).
This analysis allowed Inmarsat to map two huge ‘corridors’ for the plane’s possible location, in big arcs stretching thousands of kilometres north and south of the point where the last radar contact with MH370 was made.
Australian and US experts took this information, added some assumptions about the plane’s speed, and narrowed the southern option into an area of ocean that could be realistically searched.
Meanwhile, Inmarsat went back to its satellite data. Its new analysis found that the northern route did not quite correlate with the frequency of the pings from the plane – meaning the plane must have been heading south.
It also suggested that the plane had been travelling at a steady cruising altitude above 30,000 feet.
They compared satellite data from MH370 with that from previous Malaysian Airlines Boeing 777 flights, going back a few weeks, in order to better model the movement of the plane.
“This really was a shot in the dark,” Chris McLaughlin, senior vice president of external affairs at Inmarsat told the BBC. “It’s a credit to the scientific team that they managed to model this.
“Just a single ‘ping’ can be used to say the plane was both powered up and travelling. And then by a process of elimination comparing it to other known flights and established that it went south.”
The UK’s Air Accidents Investigation Branch also contributed to the analysis.