📸: @muhammadwickykenang || A little revision here : What does it mean when they said an aircraft is pressurised ? Cabin pressurization is a process in which conditioned air is pumped into the cabin of an aircraft or spacecraft, in order to create a safe and comfortable environment for passengers and crew flying at high altitudes. An airliner fuselage, such as this Boeing 737, forms a cylindrical pressure vessel. Pressurization becomes increasingly necessary at altitudes above 12,500 to 14,000 feet (3,800 to 4,300 m) above sea level to protect crew and passengers from the risk of a number of physiological problems caused by the low outside air pressure above that altitude. Some of the psychological problems could be Hypoxia, Attitude sickness, Barotrauma,etc. .