Before anything I’d like to say I read very interesting comments, from different people, with different views …
I’ll be corrected if I say some stupidities …
In these days of high cost energy, the biggest expense for an Airline is … FUEL !
That’s why Airlines are willing to spend big $$$ in order to hire outside companies that teach them how to save fuel and one of the easiest ways to save fuel is by avoiding to travel unnecessary fuel.
In that purpose, flight planning became very accurate (wind – temp – load – perf …), so much that when parking brake is set at the end of the day, actual fuel burn matches very well the planned one. It could be and is, sometimes, higher depending how precisely flight plan was respected and how much delay was on approach, but below … ?
Personally I don’t remember more than a couple hundred kg … but never ever more than half ton … and I’m also talking on more than 8 hours flight.
BA38 improved its fuel burn by more than 3 tons, and I believe BA Flight Planning Department to be somehow experienced.
In my view, to save 3 tons, you need to be much lighter than flight plan …
It could be interesting to compare planned and actual ZFW … if no unusual mismatch appears … then we’ll have to consider … Take Off Weight !?