non NA specific: when I'm browsing around I see civilian aircraft certified to 51,000 (G-5, learjets, etc)... why doesn't anyone get certified higher? I know.. there's not very many benefits to cruising that high.... just wondering.
For the most part, civilian aircraft try to keep the cabin pressure not higher than 8500 feet or so at their max altitude. You don't want to have health issues with the pax. Plus you don't want to have pax on O2 continually. Corporate aircraft do better with the cabin altitudes then airlines. When I flew the Piaggio, we could go to 41,000 while maintaining a cabin altitude of about 3500.
Wing and engine design also comes into the equation. Some wings will stall that high and some engines won't have any push left in them.
Going higher does not necessarily equate to better fuel brun either. Our max with pax is 410 but above 360 we don't really get a better fuel burn. We go above 360 for winds, turbulence, traffic, etc. Again, it depends on the wing and engine design.
I think the G-5 can go straight to 510 at max t/o weight.
