When using TOPCAT for take off calculations with the 800 the v speeds given by the FMC in the aircraft is about 10 knots faster than that given by TOPCAT. Anyone know why that is? Weights and temps is the same but the N1 limits are usually spot on the money. just wondering. FRED

Something is amiss. I've used topcat for ever flight and they are always within a knot or two.

Hi I never had this issue, just make sure you enter the fuel, payload, ZFW in FS actions, this should be very close if not accurate. David