B777 vref check -0 to +1 knots
Maybe someone could help me and a buddy with this question?On our B777 fleet we have a gross error check for our vref. We compare our laptop performance calculations with the FMC after all info has been entered. In our SOP s we have a tolerance of 0 to +1 knot. anyone know why?
Is it to do with the FMC working out the speed based on calculated weight at that precise moment compared to a planned TOW in the perf laptop? Or is there a more complicated scenario going on?
It's a possible upgrade question so sorry to be such a "spotter"
Thanks in advance