Originally Posted by
champair79
The bit you’ve missed is that the cabin altitude will not rise to 8000ft if you’re cruising low. Most aircraft try to pressurise the cabin close to the max allowed pressure differential (delta p) to keep the cabin altitude as low as possible. If a 777 starts cruising at say FL320, you may find the initial cabin altitude is about 7000ft. I’m plucking the numbers out of thin air (no pun intended) but hopefully that gives you some idea.
Yes. The normal operating differential is 8.6psi which at FL320 would give a cabin alt ~4,000’. I think the 787 is 9.4psi, which would give the same cabin alt of ~4,000 at FL360/370. From my observations, that’s about what you see in terms of initial cruise levels for a long-range flight in the 777-300 and 787.
If the aircraft are at the same level, then the 787 is going to have a lower cabin alt, up to 2,000 less, depending.