If you off-load a tonne of cargo to uplift a tonne of fuel, you will have about 500-600 kgs of that extra fuel left on arrival after a ULR (only 3-5 mins of fuel admittedly, but sometimes enough to reduce the 'pucker factor' and not have to commit to destination for a little longer!)
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Again not quite correct. If you exchange cargo for fuel, all other things being equal, you will arrive at destination with all of that fuel. Think about it. The 1000kg of cargo does not decrease during the flight, so why would a 1000kg of fuel reduce. This is a common error I see on the line at EK.
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