On the Airbus 340/330,when 1 pack is off or when the packs are supplied by the APU bleed,the pack flow automatically goes to high which results in an increased fuel burn of upto 1.5 percent.On a long haul flight with a burnoff of 90,000kgs this is quite a substantial amount!In my opinion,the only safe and prudent way of saving fuel is 1)landing in config3 (reduced landing flap config) 2)shutting 2 engines down on the 340 or 1 engine on the 330 after landing 3)where possible,idle reversethrust.
Switching a pack off in flight increases your fuel burn substancialy,well,at least as far as airbuses are concerned!
