Operating economics – 757 vs 738

I totally agree. It is impossible to compare two completely different aircraft in terms of the engines they use, the number of seats they have, their likely cruise altitude, as well as whatever extra weight they were carrying on the route. In addition their route length may have been slightly different depending on the approach procedure they used (the 738 could have used RNP approach for example).

As Adam Dowley says, the two calculations are completely different so of course the answers will be different. And the fact that the 757 has a higher number of seats will mean that you have divided the fuel burn down by more anyway.

Indeed the best idea would be to look at the lb per hour fuel burn for the aircraft as a whole, then you will see that the 738 uses a lot less fuel than the 757.

What you need to understand is that you are comparing two almost totally different aircraft. Looking at it, of course your final answers are going to show that the 757 is ‘more’ efficient, because the calculations are completely different.

The 757 carries more passengers than the 738, which means that you are sharing the hourly fuel burn between more seats, so the final fuel burn per seat figure is going to be lower (and in favour of) on the 757. The fuel burn per seat is higher on the 738 becuase the fuel is being shared between far fewer seats.

What you actually need to look at, surely, is the straight l/b per hour fuel burn. If you look at that, then actually, the 738 is the more efficient aircraft.

Its not a fair comparison. Fuel burn is also affected by altitude, so both aircraft would have had to have flown at the same altitude and similar winds, and the route and distance flown would have had to have been more or less identical. Also, both aircraft would have had to have the same number of seats.