[TylerE]

Twice as many flights means twice as much fuel, twice as many landing fees...

[nothrabannosir]

Those are marginal costs. Parent comment was talking about amortised costs, i.e. fixed costs. Such as the airplane, itself (depreciation per mile of flight aside, but that’s another point).

https://en.m.wikipedia.org/wiki/Marginal_cost_of_capital