> pressurization of aircraft is not required till 12,500 ft
Well, no. I don't think cabin altitude for passenger airliners has ever been that high, so you need pressurization much lower than that (typically starting around 6000 ft for modern aircraft).
Edit: Even the Boeing 307 Stratoliner was pressurized to 8000 ft.
Well, no. I don't think cabin altitude for passenger airliners has ever been that high, so you need pressurization much lower than that (typically starting around 6000 ft for modern aircraft).
Edit: Even the Boeing 307 Stratoliner was pressurized to 8000 ft.