The plane went missing on March 8 2014 en route from Kuala Lumpur to Beijing with 239 people on board. In the aftermath, British satellite telecommunications company Inmarsat used data such as the Burst Timing Offset (BTO) and Burst Frequency Offset (BFO) values to work out where the plane went. The BTO is a measure of the time taken for a transmission round trip and can be used to calculate the distance between the satellite and the aircraft.
The BFO is a measure of the relative motion of the satellite and the aeroplane.
It was the first time BFO had ever been used to try and determine the location of a missing plane.
However, used in conjunction they could be used to plot out possible routes.
The plane disappeared from air traffic control radar first, a couple of minutes after radioing in the words “goodnight Malaysia 370”.
For a short time, the jet could be detected on military radar before it dropped off from there too.
Then, only communications with Inmarsat’s satellite 3F1, called ‘handshakes’ from which the BTO and BFO values could be extracted and used to track its path.
Jeff Wise, author of The Plane That Wasn’t There, said: “We had always assumed that the transponders and radios had gone dark shortly after ‘goodnight Malaysia 370’, but the sat-com system had remained active.
“After all, whoever took the plane never used the sat-com.
“They probably have no idea it’s intermittent handshake exchanges could be used to track the plane, since the technique hadn’t been invented yet.”
The fact that these techniques were used for the first time in the MH370 investigation would imply that the person who absconded with the plane would not have known to turn the sat-com off.
However, what they actually found was that the system was turned off and then on again.
At 6:03pm UTC, 42 minutes after the plane disappeared from air traffic control radar, satellite 3F1 tried to put through a text message, but MH370’s sat-com had not responded.
Then, 22 minutes later at 6:25pm UTC, MH370 initiated a log-on with Inmarsat.
This was strong evidence, at least, that the plane had not gone down due to an electrical issue.