Pressurization

Pressurization is the process of pumping compressed air (bleed air from engines or electric compressors) into the aircraft cabin to maintain a safe and comfortable pressure altitude inside, while the aircraft flies at high altitude where ambient pressure is dangerously low.

Typical cabin pressure altitude is maintained at 6,000-8,000 ft equivalent, even when the aircraft is cruising at FL350-FL410. The pressure differential between inside and outside can exceed 8 PSI, placing significant structural loads on the fuselage. The B787 and A350 maintain lower cabin altitudes (6,000 ft) thanks to composite fuselage construction.