Editing Cabin pressurization (section)

{{Short description|Process to maintain internal air pressure in aircraft or spacecraft}}
{{redirect|Cabin pressure||Cabin Pressure (disambiguation)}}
{{Use American English|date=October 2018}}
[[File:Boeing 737 fuselage train hull 3473.jpg|thumb|An airliner fuselage, such as this [[Boeing 737]], forms an almost cylindrical [[pressure vessel]].]]

'''Cabin pressurization''' is a process in which conditioned air is pumped into the [[aircraft cabin|cabin]] of an aircraft or [[spacecraft]] in order to create a safe and comfortable environment for humans flying at high altitudes. For aircraft, this air is usually [[Bleed air|bled off]] from the [[gas turbine|gas turbine engines]] at the compressor stage, and for spacecraft, it is carried in high-pressure, often [[liquid oxygen|cryogenic]], tanks. The air is cooled, humidified, and mixed with recirculated air by one or more [[Environmental control system (aircraft)|environmental control systems]] before it is distributed to the cabin.<ref>{{cite web | url=http://blogs.howstuffworks.com/2011/04/12/how-airplane-cabin-pressurization-works-keeping-you-comfortable-in-the-death-zone-at-33000-feet/ | title=How Airplane Cabin Pressurization Works | publisher=How Stuff Works | date=April 12, 2011 | access-date=December 31, 2012 | author=Brain, Marshall | url-status=dead | archive-url=https://web.archive.org/web/20130115141028/http://blogs.howstuffworks.com/2011/04/12/how-airplane-cabin-pressurization-works-keeping-you-comfortable-in-the-death-zone-at-33000-feet/ | archive-date=January 15, 2013 }}</ref>

The first experimental pressurization systems saw use during the 1920s and 1930s. In the 1940s, [[Boeing 307 Stratoliner|the first commercial aircraft with a pressurized cabin]] entered service.<ref>{{Cite web |title=Why do aircraft use cabin pressurization |url=https://aerospace.honeywell.com/us/en/about-us/blogs/why-do-aircraft-use-cabin-pressurization |access-date=2022-08-24 |website=Honeywell Aerospace Technologies |first1=Alin |last1=Ciolac |language=en-US}}</ref> The practice would become widespread a decade later, particularly with the introduction of the British [[de Havilland Comet]] [[jetliner]] in 1949. However, [[South African Airways Flight 201#Official investigation|two catastrophic failures in 1954]] temporarily grounded the Comet worldwide.<ref name="rmjg20">{{Cite web |last=rmjg20 |date=2012-06-09 |title=The DeHavilland Comet Crash |url=https://aerospaceengineeringblog.com/dehavilland-comet-crash/ |access-date=2022-08-26 |website=Aerospace Engineering Blog |language=en-GB |archive-date=2022-09-10 |archive-url=https://web.archive.org/web/20220910013234/http://aerospaceengineeringblog.com/dehavilland-comet-crash/ |url-status=dead }}</ref> These failures were investigated and found to be caused by a combination of progressive [[metal fatigue]] and aircraft skin stresses caused from pressurization. Improved testing involved multiple full-scale pressurization cycle tests of the entire fuselage in a water tank,<ref name="rmjg20"/> and the key engineering principles learned were applied to the design of subsequent jet airliners.

Certain aircraft have unusual pressurization needs. For example, the supersonic airliner [[Concorde]] had a particularly high pressure differential due to flying at unusually high altitude: up to {{cvt|60000|ft|0}} while maintaining a cabin altitude of {{cvt|6000|ft|0}}. This increased [[airframe]] weight and saw the use of smaller cabin windows intended to slow the decompression rate if a depressurization event occurred.

The [[Aloha Airlines Flight 243]] incident in 1988, involving a [[Boeing 737-200]] that suffered catastrophic cabin failure mid-flight, was primarily caused by the aircraft's continued operation despite having accumulated more than twice the number of flight cycles that the airframe was designed to endure.<ref>{{Cite book |last=FAA |title=Aircraft Accident Report – Aloha Airlines, Flight 243, Boeing 737-200, N73711, near Maui, Hawaii, April 28, 1988 |publisher=FAA |year=1989 |page=1}}</ref>

For increased passenger comfort, several modern airliners, such as the [[Boeing 787 Dreamliner]] and the [[Airbus A350 XWB]], feature reduced operating cabin altitudes as well as greater humidity levels; the use of [[Composite material|composite]] airframes has aided the adoption of such comfort-maximizing practices.