I like the suggestion that it might be tuned to ISA 1500 AMSL altitude, if that's what you are saying. Should not be the FMS able to handle that with an optimum speed in all of the holding patterns? Okay, maybe with anti-ice...
My experience in 6-9000 altitude band was same as Lotetu's: sticking to GD +3 resulted in FF lower by around 60 kg on each side.
Last edited by FlightDetent; 13th Apr 2019 at 07:46.