Dan,
You are, of course, correct about the measured deceleration rates with autobrakes and contribution of reverse thrust having no effect on actual deceleration rate with autobrakes. I mentioned reverse thrust in the case where autobrakes, for whatever reason, are not used.
Three things are required for the autobrakes to function if they are armed:
1. Ground mode sensed; &
2. Thrust levers at idle on ALL engines; &
3. Wheel spinup has occurred.
I highlighted the "ALL" in nr 2 as in the case of Qantas 1 at BKK the autobrakes disarmed very early in the landing roll as , I believe, the nr 1 thrust lever was advanced slightly out of idle, disarming the autobrakes. Full reverse thrust, in this case, would have reduced the distance used.
747FOCAL, 250 kilos sounds a touch light, I assume you mean 250,000!! 250t is probably a little heavier than most Qantas aircraft land at LHR. I would think avg landing weight would be closer to 240. Don't quote me on that.
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