Initial cruise altitude on a 15-hour sector at MTOW (350t) would give a Max altitude of around FL300, so depending on direction of flight, and temperature, optimum would be 280/290.
After an hour or so, 310 would be achievable. Step climbing as the aircraft burns fuel.
Maximum fuel on departure would be around 140t, landing with 6-8t.
We used to carry a table for maximum altitude vs weight. Now the only reference is on the FMC.
Last edited by awair; 14th Feb 2021 at 21:02.
Reason: So it makes more sense...