I've encountered some inconsistencies using the aircraft evaluation tools in some of the aircraft families for the game.
As senior analyst in commercial aviation here is a typical rule of thumb:
Within the same aircraft family the smallest aircraft uses the least amount of fuel.
Typically up sizing increases fuel expenses by 5-10%. (A318->A319 or A332->A333 or 738->739 etc)
These aircraft have the same engines, common logic would say that the lighter smaller aircraft would need less fuel to fly.
Larger aircraft become more efficient in per seat measures, as the increase in seating is typically 20% while fuel and capital cost increase by 10%.
Also in order to get the designated range for the aircraft classes these need to be in a Typical layout. Ie. 160 seats for an 738, 150 for A320 etc.
A fully loaded A321 or 739 would not be able make a transcontinental US route, ie New York to LA with 200+ pax payload.
It would be great if for the games next update the A320, A330, B737, B767, B777, E190, CRJ families would get a fair overhaul where the smaller planes have better fuel numbers.
I would also be great if fuel consumption was dynamic, that is a standard consumption for the aircraft on the route empty, and a small percentage bump as you add pax and cargo on the aircraft.
These features would definitely make fleet decision making more strategic and more demand driven.
I hope the suggestion gets considered.