(in prepar3d using stock fsx 744) Just made a 8904nm NON-STOP 19 hour trip (cape town direct to san francisco with the use of time warp obviously) in a fully loaded 747-400, with 7% fuel (~1 hour of endurance, maybe 400nm more range) to spare upon landing. *this is a east to west flight, so the return trip would’ve required and consumed even less fuel thanks to jet stream and Coriolis effect. And given the 747 doesn’t have the applicable autopilot mode I had to do the entire flight in 100feet 100fpm increments on the autopilot manually, it would’ve been even more efficient if the job was the autopilot’s instead. (and okay, maybe fsx isn’t the most realistic, but the figures can’t be that off?)
The 747-400’s official maximum range is 7,260nm but this figure was greatly extended (even if you factor in the reserve fuel for the original figure) with the technique of cruise-climbing in which manually or via autopilot the cruise IAS is maintained by adjusting the plane’s altitude, gradually climbing as the plane loses weight. I eventually got to 50,000ft and cruised there for a whole other hour there before starting my decent 200nm from KSFO.
The technique is unfortunately somewhat unfeasible in the current atc system because human atc prefer planes to stay on a linear flight path preferably at an altitude that has a whole number, while cruise climbing is incremental, especially at high altitudes where it needs ridiculously low climb rates. The range increase/fuel saved is apparently not worth it, also any sudden 40kt gust of tail wind would have stalled out my plane.
The Concorde actually used this method and was allowed to since the altitude it flew in was mostly unpopulated high altitude airspace and thus ATC wasn’t that much of an issue.