There have been some major fuel burn issues/irregularites on some aircraft for a long time. For example:
- On the CRJ and A350 the most efficient altitude is very low (below FL350). This is especially inaccurate for the A350 because FL350/360 is often the initial cruising altitude of long flights.
- The 757 has a very big jump in optimal altitude from 320 straight to 370.
- The 747’s fuel burn increases from 300 to 340 (or somewhere around there) but then decreases again at higher altitudes at lower weights, and as such FL300 is always most efficient.
There is also the lesser problem of many aircraft favoring lower altitudes than IRL (The only aircraft types that I know don’t have this issue are the 767, A380, and to some extent 788*). Also most aircraft favor higher speeds.
Will the devs address these issues at some point and give us a more realistic flight experience? Especially, if the numbers in IF matched closer with those in simbrief it would be much easier to do fuel planning.
- The 788 fuel burn seems to be constant above a certain altitude, and that makes it kind of favor the lower altitude since speed of sound decreases with altitude up to around FL300-400 depending on weather.
PS. It has long been a “feature” of IF that some aircraft have lower fuel burn than IRL and thus can fly for much longer (eg. 767, A350). I think it could be a good idea to allow these to stay by giving a larger fuel tank than IRL like on the B737 so that liveries that are only available on a shorthaul aircraft can fly longer routes non-stop.