I guess these cant be simple definitions, I would expect them to be amazingly complex and in some instances unable to actually define due to unknowns.
The path followed from a to b is never going to be the same as b to a, differences in flight level, atc route, wind directing differences from opposite heading, lighter aircraft as you dont have as much fuel, change of c of g.
I assume that given that optimum flight level changes with weight then as well as heading FL rule change optimum level will change too.
so it may have taken 2 hrs and X amount of fuel to get to point b but to go back to point a may take more or less time or fuel.
does this mean it cant be calculated until actual is known ? (ie dynamic point of no return) or is it kept simple ? or is it planned (as in this is how we would get back) ?
not trying to be clever.. just learning !