In the case of Fsbuild2 there are no burn values for FL180 in the FSB2 767 performance file, so actually your getting the burns for FL240 the closest altitude to FL180 it had cruise data for. I don't think our 767 POH had burn numbers for FL180.You'd have to plug-in in some cruse burn numbers for FL180 to get things closer to accurate for this kind of short haul route at FL180.Also if you do not include a TOC/TOD waypoint that may increase the climb burn calc if the first waypoint is much further away than the TOC waypoint would be.Regards.Ernie.

I have the Air Do dvd. Its a 1 hour flight from Sapporo to Tokyo and the flight level were FL 350, 370, 390 & 410. One of the flight reached 410 in 14 minutes, the V/S was 6,000YV