Is pressure inside Jet plane is nearly 1atm when it flying?
The term “Nearly” isn’t very specific. While many aircraft use pressurized cabins to aid the occupant’s breathing, the systems don’t maintain sea level pressure through the entire flight. Maintaining the equivalent of some altitude between sea level and 10,000 feet reduces the mechanical stress on the fuselage’s structure. Most structures, including things other than aircraft, are better able to tolerate SOME stretch and/or flex that be so thick (thus heavy) as to be essentially inflexible. Allowing the cabin pressure to simulate a somewhat higher altitude doesn’t stretch it quite as much and allows the aircraft a longer service life without lowering the pressure enough to endanger the occupants. Regulations vary in different countries, but there are often limits on the time an aircraft can be above 10,000 feet above sea level without cabin pressurization OR all occupants using supplemental oxygen supplies (masks or those nasal tubes). Oxygen and/or pressurization is eventually require
