RamerinianAir's answer is technically correct. But there needs to be more of an applied perspective:
|Quoting OldAeroGuy (Reply 4):|
The favored method is to compare the Block Fuel per Seat used on a specific mission with a full passenger payload and no cargo that is consistent with the general range characteristics of the two airplanes being compared. A320 vs B737 might use 1000 n.m. while A346 vs 773ER might use 4000 n.m. Block fuel includes fuel used for Taxi Out/In, Takeoff, Climb, Cruise, Descent, and Approach.
Correct, but the analysis I have participated always use "target routes" with varying winds and such. CO
did it the most straight forward way to decide which regional jet they preferred. They had a CRJ-200 and an ERJ-145 take off within minutes of each other loaded with the same number of "volunteers" and the luggage was weighted to have within a few pounds the same. The FAA was in on the test as they assigned the two the exact same flight levels per CO
For most sales orders, everything was done at TSFC and appropriate thrust levels the airframe required at Takeoff, Takeoff +27F, initial climb, mid-climb, end of climb, start of cruise, mid-cruise, end of cruise, and approach. From this most customers could predict fuel consumption to within 0.5% (on an annualized average). All of these numbers were produced for light loads, max pax (no cargo), and max payload plus any subsets a customer would require.
If it seems overly complicated, its because it is complicated. An airbus 320 is very efficient for long haul, but the 738 gains on the short haul just because its lighter. Its a constant trade. But it does come down to mass fuel consumed per distance traveled per pax.
Oh, a 757 uses less than half the fuel of a 707, the best link I found. Note how efficiency is a function of range on slide 16:
The space is messing up the link: