330/340 Altitude Fluctuation

[Guest cocoarevo]

Hi,When in autopilot managed cruise, my altitude slowly fluctuates by ~10-15 ft. I'm not using acceleration, and I am within weight limits and am at the OPT CRZFL suggested by the MCDU. I'm not even sure if it's a problem, but I would like to know. Thanks,cocoarevo

[Guest cobrafly]

according to the real flight, it is not a problem at all, once in CRZ flight "ALT CRZ", the AP reverts to wat it's called: "soft cruise" MODE.this mode is for flight confort:- instead of making corrections, to maintaine speed, by varying engine thrus several times (back and forward....), the AP will maintain speed by varying the pith attitude (decel=> pitch up; accel=> pitch down). for that it allows small altitude variation arround CRZ ALT.actually 10-15ft is nothing since in real aircraft it goes intill +/- 50-70FT.