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It is really amazing that the theory of a double flame-out, for fuel exhaustion / pollution /icing-waxing, keep turning up in spite of the information that has been given to us.
What we know, from the AAIB, is
The F/O was handling the approach (Question : A/P on or manual with FD ? )
Down to a height of 600 ft, the approach parameters were quite normal.
The engines were not responding to throttle demands (Question : One or both ? )
The aircraft was in a low energy state (Question : Due to the insufficient engine (s) output ?)
What we do know :
The aircrew has had a long 12-hour daylight flight before their approach to Heathrow and were probably past their peak of alertness.
The aircraft went below the ILS glideslope and touched-down 100 ft below said glide. That's not very much, if one puts the events into perspective.
The weather conditions were fair but there had been a forecast of instability and possible windshear over the British Isles on the zones ahead of a frontal occlusion and throughs.
There have been some instances of engines on the 777 not respoding to throttle commands. To the effect that there is a procedure to that effect. (granted, GE, not RR ).
My argument lies on the premise that a *hung thrust* is very hard to detect from a pilot's point of view. One would start to notice it, as the failure is in essence very subtle, only when the thrust demand becomes rather high, relatively to a normal required engine EPR.
As a matter of fact, if one omits the speed tape, all the approach parameters would seem normal : On the glide, FD bars crossed in the center of the PFD, EPRs coherent with the approach conditions. The only other visible clue that something is becoming quite wrong would also be the unusual pitch attitude, somewhat higher than normal, but the clue would be easily hidden by the *normallly*crossed command bars of the FD.
We now have the beginning of the ever worsening trap we all dread : A decaying airspeed, an increasing drag situation requiring more thrust that is not available any more which causes the speed to decay further while the AoA is increasing to achieve the "stay on glide" requirement...and so on....
At that point, the thrust required for exiting the situation would have been very important and from a piloting aspect we are probably close to a stall recovery-type of handling.
That close to the ground ? IMHO, some feat of reflex-flying !
Did I forget to say that as the F/O was handling the aircraft, that information taken in itself destroys the ideas of a double engine flame-out, as in this case, the only instruments available through the battery, would have been the captain's ? And neither the APU or the RAT would have enough time to come on-line.