If I’m reading that chart correctly, the autopilot would have had to fly the first hour at 307 mph and the last hour at 700mph — and that not only bad autopiloting, but it’s also impossible.
++++++++
Could be but the plot must be a projection from points on a sphere to a flat surface so that would need to be taken into consideration. Plus I don’t understand how whoever made this plot drew the straight line. As you noted, they should have used constant velocity to choose the points and then see if that curve maps to straight line.
Despite the plot, they must have done that to draw the conclusion they did. Don’t you think?
That straight line is the yellow flight path here drawn by the NTSB:
https://www.facebook.com/178566888854999/photos/pcb.740971779281171/740971732614509/?type=1&theater
It’s not that far for the sphere to significantly come into play. But you can recheck the numbers here:
http://www.nhc.noaa.gov/gccalc.shtml
It’s either autopilot or Inmarsat arcs — it can’t be both.