The official location of the missing Malaysia Airlines jet is the Indian Ocean, based off data called the Burst Frequency Offset (BFO). Mr Wise said: “Just as the motion of a speeding train makes the tone of its whistle go up or down, the relative motion of the satellite and the aeroplane shifts the frequency of the radio signals transmitted between them. The BFO is a measure of this difference.”
From previous data, Inmarsat had already worked out the plane had flown in one of two directions – a northern pathway and a southern pathway.
The north corridor would have seen the plane end up somewhere in the Kazakhstan, the south corridor in the Indian Ocean, west of Perth.
By working out what factors affect the BFO value, Inmarsat could calculate the value they would expect to see if the plane had flown north versus if it had flown south.
The difference between the values would be “stark”.
Once they had worked this out, they found that the BFO values recorded by their satellite was much closer to the expected value for if the plane flew south compared to if it flew north.
This is how the authorities used the data to conclusively state flight MH370 ended in the Indian Ocean.
Mr Wise said: “No one had ever tried to use BFO values to try to determine the location of a missing plane before.
“Inmarsat had had to figure the analysis out from scratch and this task turned out to be daunting.”
There were many factors that could affect the BFO, such as the speed, heading and location of the plane, the speed and location of the satellite, as well as the relative motion of the satellite and the ground station.
Despite the obstacles, Inmarsat managed to come up with a mechanism of understanding BFO values with “reasonable accuracy”.
They checked their method by calculating BFO values for planes that had actually been in the air at the same time as MH370 and comparing these with the real recorded values.
These matched, confirming their hypothesis.
Inmarsat scientist told BBC’s Horizon: “The graphs matched, the data worked, the calculation was solved.”
This proved that MH370 had in fact crashed into the Indian Ocean.
They then decided to combine this data with other data, such as the Burst Timing Offset, in order to work out the exact location of MH370 within the ocean.