Yes...
Three mile error....no problem...that's on the individual IRUs. But, the actual FMGC positions should have been close to correct.
Again, if the ground speed is five knots or less....no problem.
In fact, the FMGCs look at individual IRU drift...account for their drift....as time goes on, the FMGCs actually 'learn' the IRUs and compensate.
I have to say...if we follow the checks and balances that are given us in the SOP, none of this is an issue. We check our position on the ground by looking at ground-based navaids (if possible)...(use raw data and compare it to what's in the FMGC when you stick the navaid in there)...look at the position of the aircraft on the ND, comparing it to the airport diagram...etc., etc. We also check the bearing and distance of the first fix...so, all is well when you push 'em up to Flex/TOGA (The airplane then 'knows' where it is EXACTLY...and you've verified where it's going.) (Looking at the bearing and distance of the first fix is different on GPS aircraft, since those figures are based on your actual position (at the gate)...vis-a'-vis the first fix...but that's OK.)
It's all good....
PantLoad