Originally Posted by
Jumpjim
I would suggest that the loss of energy is due to the double engine failure rather than crew actions?
Jeez, you people....
At the point at which the engine failure became obvious, the plane had X amount of energy - some was potential energy, some kinetic energy. The need was to manage this energy to conserve as long as possible, which means flying the plane in the most efficient way e.g. at best L/D. Unfortunately that's not what the autopilot did - apparently it tried to maintain the glide slope, which will have frittered the energy away.
If you fly too slowly (which is what the autopilot did) you increase the induced drag, too fast and you incrase the form drag. Both will result in the plane not flying as far as it could for the original amount of energy.
See the total drag vs. speed diagram on this URL - where the two cross is the best L/D ratio, and the best speed to fly for the situation G-YMMM was in. Unfortunatly the crew had very, very little time to think about it.
http://pilotsweb.com/principle/liftdrag.htm