Mcdu Showed Wrong Distance

[chopperspring]

yesterday i flow a airbus which had two mcdus show different route distance to the same destination, one showed 70nm while another one showed 55nm. the remaining route was the same on both Mcdus, anybody know what might cause this problem?(i dont think it's map drift) tks

[Otto Throttle]

Not familiar with the specific equipment fit on the 'Bus, or how their MCDUs may be linked, but distance to go shown can be altered depending upon what arrival is in the 'box', including any holding.

On my type, both MCDUs will display the same info, but the distance to go can be misleading as the system always works (initially at least) on the full procedural arrival rather than the more likely vectored approach, and if a hold is also entered into the arrival, the system builds in what appears to be at least 2 holds in terms of both time and distance.

This may be what you are seeing.

[chopperspring]

thank u, but i think it might be something else. in that flight, my captain was PF, i am PNF, so basiclly PF orperated and modified his MCDU and then the info in his mcdu will be transferred to my fmgc then mcdu automatically, i just did "confirmed" part, which made sure that the info in both mcdus were exactly the same, however the result,by result i mean distance was different, that's why it confused me and my captain...

[toby320]

may be your captain did some change in your rute and forget to clear somthing, you can use your scondary flight plan and check the original rute:bored:

[Sid Starz]

I've also seen the same thing occasionally on the 757. There will be a discrepancy of a few miles or a minute or two between the two FMC's, usually for only a few minutes. Not too sure why! Possibly small IRS differences?