Did a flight with the 787 and reached cruising altitude of 40000 feet. For some reason when I reached it, it started going up and down, had to go a bit lower to stop the issue. Is it because of the trim or is the altitude ceiling different in IF than IRL?
You’re probably too high for your weight.
This is also important. If you aren’t trimmed properly, it can make the aforementioned issue of being too heavy, worse. When in the air, you want to make sure there is no coloured line visible in the trim box. If the line is going down from the middle, you need more positive trim, and vice versa.
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This usually happens when the aircraft is right at the edge of its performance for the current weight and altitude. At FL400, even small changes in speed or trim can cause the aircraft to slowly climb and descend.
Reducing weight, cruising a bit lower, or fine-tuning trim and speed normally stabilizes things. It’s something I’ve noticed as well on long-haul flights in similar conditions.
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