It may have something to do with the way that speed ("S") is derived. FCOM "... Equal to about 1.22 tp 1.25 Vs of the clean configuration..."
Assume that you have 70 Tonnes in your MCDU at take-off, but your actual FAC computed weight is several tonnes more, BUT not enough more to cause a "Check Gross Weight" message.
MCDU is computing speed from the wieght you entered...
PFD is reading FAC computed speed...
This may explain what you saw.
Last edited by Jimmy Do Little; 14th July 2009 at 16:39.