How MH370's trajectory was traced to the southern arc

LONDON - Engineers of Inmarsat Plc huddled together for days in a marathon data-crunching session to help find the last known location of Malaysian Air Flight 370 which went missing hours after take-off from Kuala Lumpur on March 8.

The flight MH370 was meant to reach Beijing the next morning but fell off the radar, and was declared missing by Malaysian prime minister Najib Razak on Monday, more than two weeks later. He proclaimed that the plane's voyage had ended in a remote part of the Indian Ocean, a revelation he attributed to Inmarsat and the AAIB's findings.

However, initial report from one of Inmarsat's satellites, handed to investigators on March 11, had only helped investigators establish two possible arcs taken by the MH370 - one expanding over the northern corridor while another over the southern corridor.

Days after the initial trajectories were revealed, engineers using "groundbreaking but traditional mathematics-based process", nailed down the flight path over the Indian Ocean, Aviationweek reported.

So how did they determine the southern arc as its flight path?

Their conclusions were based on research using the Doppler effect - a theory named after the Austrian physicst Christian Doppler who proposed that frequency of a sound wave emitted from an object changes relative to its distance from an observer.

In case of the missing plane, the aircraft had reportedly sent six "pings" to the Inmarsat satellite over the course of six hours when it flew undetected over the ocean with its transponders switched off. The pings - termed as handshakes - were sent from the in-built antenna of the Boeing aircraft to one of the 10 Inmarsat satellites. The satellite was sending hourly "polling signals" to the Boeing 777, which as long as it was operating, sent back acknowledgement signals. The pings stopped after the sixth hour.

Engineers determined the "Doppler shift" - which means they calculated the ever so slight changes in the ping frequencies, caused due to the movement of the aircraft relative to the satellite.

The teams compared equivalent data from flights of other Boeing Co. 777 jets in and out of the area to see where the Doppler effect would result in a pattern that matched the data from Flight MH370.

"They worked together for six or seven days straight," said Inmarsat spokesman Chris McLaughlin, with the international team unwinding at the in-house gym during breaks or fetching pizza to sustain the round-the-clock mission. "What we discovered was that the northern projected path had no correlating pings appear on it, while for the southern projected path, we had frankly an absolute correlation. The plotted positions, the plotted lines all matched each other," Bloomberg reported.

The team's breakthrough came on March 21, when it was able to rule out the northern corridor and hone in on the lower end of the southern axis.

"The new analysis was convincing enough for the AAIB to brief the Prime Minister that the aircraft flew in the southern corridor," Malaysian acting Transport Minister Hishammuddin Hussein told a press conference Tuesday. 'This type of analysis has never been done in an investigation."