My original work on MH370’s flightpath relied primarily on ping ring radii and fixed landmarks. The satellite’s ground point, as well as the GPS for Boarding Gate C-1 at Kuala Lumpur airport, allow us to pinpoint the plane’s endpoint on its final ping with the centuries-old technique known as trilateration. While that technique tells us where the plane was on the final ping, it does not tell us if the plane was still airborne or in the water. So, we can’t assume the plane is straight down from its location on the final ping, although there are reasons to believe it is nearby if not straight down.

And we now have one more technique that allows us to verify the accuracy of the final ping location. This additional technique harnesses Inmarsat’s station-keeping data that is used to help ensure satellites are where they are supposed to be.

This method is as straightforward as the original ping ring method. It resolves to give us the length of the Sagitta, which is then used to place the plane’s final ping location.

This is how the technique works. Inmarsat’s station-keeping records give us the angle between the plane, earth’s center, and the 3F-1 satellite while boarding prior to the flight: 37.27 degrees. Then, eight hours later when it crashed, the angle between the plane, earth’s center, and the satellite had grown to 43.83 degrees, an increase of 6.56 degrees, which is 1.82% of earth’s circumference. That 1.82% translates into 730 kilometers, which we already know is the length of the Sagitta or depth of the arc between the airport and the final ping. That is exactly the same linear distance one gets by subtracting the satellite-to-airport radius (4,149 km) from the satellite-to-final-ping radius (4,879 km) , but was obtained from satellite positioning rather than ping ring annulus measurement. It reconfirms the accuracy of the original technique.