The top cruise altitude of the longitude is FL450. When I choose AUTO for altitude and enable step climb planning, SimBrief almost always uses FL410 with no climb steps. This is true even when going from east to west, where the flight level should be even instead of odd. Occasionally it’ll choose FL430, but never with any steps, and never to the max cruise altitude.
Above FL410 you are no longer in RVSM airspace, and the buffer between altitudes becomes 2,000ft. This means that valid altitudes are as follows (source):
Eastbound: 370 390 410 450
Westbound: 360 380 400 430
So even when flying east to west, you’ll never be planned at FL440 for example.
I’ve made some adjustments to the cruise altitude calculations for business jets. When planning an eastbound flight, assuming the aircraft is light enough (you can set 0 passengers/cargo to make sure), SimBrief should plan FL450 from what I can see.
I’m still a bit confused. I planned a flight from PHOG to KACV and it had me climb to FL430 initially and then descend to FL410. Is this because I was under radar coverage until I hit the oceanic airway?
Also, shouldn’t it have me climb to FL450 after enough fuel has burned off?
Depends. Initially you were probably too heavy to make it to FL450 due to the fuel load required. Later on in the flight, FL450 might have become possible, but if that only occurs 30 minutes before you’d need to descend, it’s more efficient to stay at FL410 at that point.
FL430 was chosen initially because you are technically flying westbound until AUNTI (heading 349 or so). Then after AUNTI, you are flying eastbound, so FL410 was chosen (and you were too heavy for FL450 at that point).
This makes sense but I think there might still be an issue with the Longitude performance profiles not having been updated since MS made improvements (as discussed in other threads). I’m seeing ~360 lb/h difference between FL410 and FL450. Even when I can’t reach full speed at 450, it still seems to be more efficient.
In particular, I was able to climb to FL450 starting at HALLI and was able to reach M.84 with another 2h11m until TOD. Estimated landing fuel went up by ~1000 lbs
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