Originally Posted by
JDiver
recalculations of probable route and reduced range caused by higher speeds increasing fuel consumption. That's pretty much what has been announced by the Malaysian government et al.
The air in the atmosphere moves relative to the ground (ocean surface), so there are two "speeds" to calculate: Airspeed (speed of 777 relative to the air) and Groundspeed (speed of 777 relative to the ground).
Airspeed is a function of the fuel burn rate while the Groundspeed is what they need in order to calculate where the flight ended. (Groundspeed multiplied by the time flown will give the distance to the point where the flight ended.)
My reading of the updates is that the recalculations found a higher air speed and lower ground speed than originally calculated.
(I suspect that air and ground speed data from the search planes' flights gave them data about wind patterns, data that they did not have when they did the earlier calculations.)