A320 MCDU Difference in Distance to Go
Hi,
A few weeks ago during descent after a 4 hour sector on the A320, we noticed that the 'Distance' (ie distance to go, track miles) at the bottom of MCDU 1 was about 5nm more than that indicated on MCDU 2.
In addition, we were slightly high on profile - PROG page on MCDU 1 (and donut on Captain's PFD) indicated about 450ft high on profile, whereas FO's PROG page and donut indicated about 1800ft high on profile. AP 1 engaged, and managed descent seemed to be taking its lead from the Captains side as you'd expect.
The Position Monitor page indicated that the IRS's hadn't drifted any more than normal (less than 2nm each), aircraft remained in GPS Primary, NAV Accuracy High at all times in the descent, and a manual check of nav accuracy on both sides showed we were where the map thought we were. We put a nearby VOR in the PROG page and both MCDUs indicated the same distance to the VOR, just the flight plan track miles were different.
FMS 2 A321, getting on a bit.
Any ideas what could cause this? We were stumped, but it was 5 in the morning....
Cheers,
ET