Small mention to add since my topic isn’t closed yet, the A350-900 also has this issue as well. Did more testing. I haven’t checked the exact n1 it takes for this fuel break to happen though. I do know this does persist until passing 29,000 like the a330s.
The a350 has a bigger break than the a330. From 0 - 10,000 feet, you will have a burn increase even with constant power if you are below 50.0% n1. If you are above 50.0% n1, you’ll have the opposite. 50.0% n1 looks like there’s no change in fuel burn. Passing 10,000 feet however, this effect gets thrown out the window and it doesn’t matter where the throttle is; you’ll always have more burn. In other words, it doesn’t matter whether you’re below/at/above 50.0% n1 because you WILL have more burn when you fly higher, maintaining n1. And then at 29,000 feet it breaks again and you have a decrease. Maybe i have to double check the a330 as well. Very strange to me.
Changing this now to 49.9% n1. If you exceed it, you’ll have a decreasing burn rate under 10,000. If you are at 49.9% and under, you’ll have an increasing burn rate under 10,000. One more shocking thing to me is that the a350 and a330 fuel burn for an idle descent through 10,000 is capped at 3,390 lbs/hr. The a330 also starts increasing burn at 49.9% n1 while climbing to 10,000. Passing 10,000 for the a350 only, there’s no decreasing no matter the throttle till 29,000+. Is there a particular reason why this is? I’m sorry if I’m bumping my old topic a bit, but I’m seeing new discoveries in the numbers and I’m sharing what I find along the way since I don’t see a lot of people testing (and/or care to test) this far. It should make it easier to pinpoint an issue like this if you can find out where and when it happens.