Editing Cabin pressurization (section)

==History==
[[File:Cessna P210N (N6623W) in flight.jpg|thumb|Cessna P210 - First commercially successful pressurized single-engine aircraft]]
The aircraft that pioneered pressurized cabin systems include:
* [[Packard-Le Père LUSAC-11]], (1920, a modified French design, not actually pressurized but with an enclosed, oxygen enriched cockpit)
* [[Engineering Division USD-9A]], a modified [[Airco DH.9A]] (1921 – the first aircraft to fly with the addition of a pressurized cockpit module)<ref>Harris, Brigader General Harold R. USAF (Ret.), “Sixty Years of Aviation History, One Man's Remembrance,” journal of the American Aviation Historical Society, Winter, 1986, p 272-273</ref>
* [[Junkers Ju 49]] (1931 – a German experimental aircraft purpose-built to test the concept of cabin pressurization)
* [[Farman F.1000]] (1932 – a French record breaking pressurized cockpit, experimental aircraft)
* [[Chizhevski BOK-1]] (1936 – a Russian experimental aircraft)
* [[Lockheed XC-35]] (1937 – an American pressurized aircraft. Rather than a pressure capsule enclosing the cockpit, the [[monocoque]] fuselage skin was the pressure vessel.)
* [[Renard R.35]] (1938 – the first pressurized piston airliner)
* [[Boeing 307 Stratoliner]] (1938 – the first pressurized airliner to enter commercial service)
* [[Lockheed Constellation]] (1943 – the first pressurized airliner in wide service)
* [[Avro Tudor]] (1946 – first British pressurized airliner)
* [[de Havilland Comet]] (British, Comet 1 1949 – the first jetliner, Comet 4 1958 – resolving the Comet 1 problems)
* [[Tupolev Tu-144]] and [[Concorde]] (1968 USSR and 1969 Anglo-French respectively – first to operate at very high altitude)
* [[Cessna P210]] (1978) First commercially successful pressurized single-engine aircraft<ref>{{cite web |last1=New |first1=Paul |title=All Blown Up |url=https://www.tennesseeaircraft.net/2018/05/17/all-blown-up/ |website=Tennessee Aircraft Services |access-date=21 May 2021 |date=May 17, 2018 |quote=The P210 wasn’t the first production pressurized single engine aircraft, but it was definitely the first successful one.}}</ref>
* [[SyberJet SJ30]] (2005) First civilian business jet to certify 12.0 psi pressurization system allowing for a sea level cabin at {{cvt|41000|ft|0}}.<ref name="Cornelisse">{{cite book|author=Cornelisse, Diana G.|title=Splended Vision, Unswerving Purpose; Developing Air Power for the United States Air Force During the First Century of Powered Flight|location=Wright-Patterson Air Force Base, Ohio|publisher=U.S. Air Force Publications|year=2002|isbn=0-16-067599-5|pages=128–29}}</ref>

The first airliner to enter commercial service with a pressurized cabin was the [[Boeing 307 Stratoliner]], built in 1938, prior to [[World War II]], though only ten were produced  before the war interrupted production. The 307's "pressure compartment was from the nose of the aircraft to a pressure [[Bulkhead (partition)|bulkhead]] in the aft just forward of the horizontal stabilizer."<ref>William A. Schoneberger and Robert R. H. Scholl, ''Out of Thin Air: Garrett's First 50 Years'', Phoenix: Garrett Corporation, 1985 ({{ISBN|0-9617029-0-7}}), p. 275.</ref>

[[File:B-8 winter helmet & A-14 oxygen mask (1944).jpg|thumb|World War II era flying helmet and oxygen mask]]
World War II was a catalyst for aircraft development. Initially, the piston aircraft of World War II, though they often flew at very high altitudes, were not pressurized and relied on oxygen masks.<ref>Some extremely high flying aircraft such as the [[Westland Welkin]] used partial pressurization to reduce the effort of using an oxygen mask.</ref> This became impractical with the development of larger bombers where crew were required to move about the cabin.  The first bomber built with a pressurised cabin for high altitude use was the [[Vickers Wellington#Bomber variants|Vickers Wellington Mark VI]] in 1941 but the RAF changed policy and instead of acting as [[Pathfinder (RAF)|Pathfinders]] the aircraft were used for other purposes. The US [[Boeing B-29 Superfortress]] long range strategic bomber was first into bomb service. The control system for this was designed by [[Garrett AiResearch|Garrett AiResearch Manufacturing Company]], drawing in part on licensing of patents held by Boeing for the Stratoliner.<ref>{{cite journal |author=Seymour L. Chapin |title=Garrett and Pressurized Flight: A Business Built on Thin Air |journal=Pacific Historical Review |volume=35 |issue= 3|pages=329–43 |date=August 1966 |doi=10.2307/3636792|jstor=3636792 }}</ref>

Post-war piston airliners such as the [[Lockheed Constellation]] (1943) made the technology more common in civilian service. The piston-engined airliners generally relied on electrical compressors to provide pressurized cabin air. Engine supercharging and cabin pressurization enabled aircraft like the [[Douglas DC-6]], the [[Douglas DC-7]], and the Constellation to have certified service ceilings from {{cvt|24000|to|28400|ft|0}}. Designing a pressurized fuselage to cope with that altitude range was within the engineering and metallurgical knowledge of that time. The introduction of jet airliners required a significant increase in cruise altitudes to the {{cvt|30000|-|41000|ft|0}} range, where jet engines are more fuel efficient. That increase in cruise altitudes required far more rigorous engineering of the fuselage, and in the beginning not all the engineering problems were fully understood.

The world's first commercial jet airliner was the British [[de Havilland Comet]] (1949) designed with a service ceiling of {{cvt|36000|ft}}. It was the first time that a large diameter, pressurized fuselage with windows had been built and flown at this altitude. Initially, the design was very successful but [[South African Airways Flight 201#Official investigation|two catastrophic airframe failures in 1954]] resulting in the total loss of the aircraft, passengers and crew grounded what was then the entire world jet airliner fleet. Extensive investigation and groundbreaking engineering analysis of the wreckage led to a number of very significant engineering advances that solved the basic problems of pressurized fuselage design at altitude. The critical problem proved to be a combination of an inadequate understanding of the effect of progressive [[metal fatigue]] as the fuselage undergoes repeated stress cycles coupled with a misunderstanding of how aircraft skin stresses are redistributed around openings in the fuselage such as windows and rivet holes.

The critical engineering principles concerning metal fatigue learned from the Comet 1 program<ref>{{cite journal|title=Behaviour of Skin Fatigue Cracks at the Corners of Windows in a Comet Fuselage|author=R.J. Atkinson, W.J. Winkworth and G.M. Norris|journal=Aeronautical Research Council Reports and Memoranda |year=1962|citeseerx=10.1.1.226.7667}}</ref> were applied directly to the design of the [[Boeing 707]] (1957) and all subsequent jet airliners. For example, detailed routine inspection processes were introduced, in addition to thorough visual inspections of the outer skin, mandatory structural sampling was routinely conducted by operators; the need to inspect areas not easily viewable by the naked eye led to the introduction of widespread [[radiography]] examination in aviation; this also had the advantage of detecting cracks and flaws too small to be seen otherwise.<ref>Jefford, C.G., ed. [https://web.archive.org/web/20110105083157/http://www.rafmuseum.org.uk/research/documents/Journal%2026%20-%20Seminar%20the%20RAF%20and%20Nuclear%20Weapons%201960-98.pdf ''The RAF and Nuclear Weapons, 1960–1998.''] London: Royal Air Force Historical Society, 2001. pp. 123–125.</ref> Another visibly noticeable legacy of the Comet disasters is the oval windows on every jet airliner; the metal fatigue cracks that destroyed the Comets were initiated by the small radius corners on the Comet 1's almost square windows.<ref name="Davies and Birtles pp. 30–31">Davies, R.E.G. and Philip J. Birtles. ''Comet: The World's First Jet Airliner''. McLean, Virginia: Paladwr Press, 1999. {{ISBN|1-888962-14-3|}}. pp. 30–31.</ref><ref name="Munson p. 155">Munson, Kenneth. ''Civil Airliners since 1946.'' London: Blandford Press, 1967. p. 155.</ref> The Comet fuselage was redesigned and the Comet 4 (1958) went on to become a successful airliner, pioneering the first transatlantic jet service, but the program never really recovered from these disasters and was overtaken by the Boeing 707.<ref>{{cite web |url=https://www.researchgate.net/publication/287199920 |title=Milestones in Aircraft Structural Integrity |website=[[ResearchGate]] |access-date=22 March 2019}}</ref><ref>Faith, Nicholas. ''Black Box: Why Air Safety is no Accident, The Book Every Air Traveller Should Read''. London: Boxtree, 1996. {{ISBN|0-7522-2118-3|}}. p. 72.</ref>

Even following the Comet disasters, there were several subsequent catastrophic fatigue failures attributed to cabin pressurisation. Perhaps the most prominent example was [[Aloha Airlines Flight 243]], involving a [[Boeing 737-200]].<ref>{{cite web | url=https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR8903.pdf | title=Aircraft Accident Report AAR8903: Aloha Airlines, Flight 243, Boeing 737-200, N73711 | publisher=[[NTSB]] | date=14 June 1989}}</ref> In this case, the principal cause was the continued operation of the specific aircraft despite having accumulated 35,496 flight hours prior to the accident, those hours included over 89,680 flight cycles (takeoffs and landings), owing to its use on short flights;<ref name=ASN>[http://aviation-safety.net/database/record.php?id=19880428-0 Aloha Airlines Flight 243 incident report - AviationSafety.net], accessed July 5, 2014.</ref> this amounted to more than twice the number of flight cycles that the airframe was designed to endure.<ref name="AAR-89-03 Final Report" /> Aloha 243 was able to land despite the substantial damage inflicted by the decompression, which had resulted in the loss of one member of the cabin crew; the incident had far-reaching effects on [[aviation safety]] policies and led to changes in operating procedures.<ref name="AAR-89-03 Final Report">{{cite web |url=https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR8903.pdf |title=Aircraft Accident Report, Aloha Airlines Flight 243, Boeing 737-100, N73711, Near Maui, Hawaii, April 28, 1998 |date=June 14, 1989 |publisher=[[National Transportation Safety Board]] |id=NTSB/AAR-89/03 |access-date=February 5, 2016}}</ref>

The supersonic airliner [[Concorde]] had to deal with particularly high pressure differentials because it flew at unusually high altitude (up to {{cvt|60000|ft|0}}) and maintained a cabin altitude of {{cvt|6000|ft|0}}.<ref>{{cite journal|last1=Hepburn|first1=A.N.|title=Human Factors in the Concord|journal=Occupational Medicine|date=1967|volume=17|issue=2|pages=47–51|doi=10.1093/occmed/17.2.47}}</ref> Despite this, its cabin altitude was intentionally maintained at {{cvt|6000|ft|0}}.<ref>{{cite journal |doi=10.1093/occmed/17.2.47 |title=Human Factors in the Concorde |journal=Occupational Medicine |last=Hepburn |first=A.N. |volume=17 |issue=2 |year=1967 |pages=47–51}}</ref> This combination, while providing for increasing comfort, necessitated making Concorde a significantly heavier aircraft, which in turn contributed to the relatively high cost of a flight. Unusually, Concorde was provisioned with smaller cabin windows than most other commercial passenger aircraft in order to slow the rate of decompression in the event of a window seal failing.<ref name = 'nunn'>{{cite book |title = Nunn's applied respiratory physiology |first = John Francis |last = Nunn |publisher = Butterworth-Heineman |isbn = 0-7506-1336-X |year = 1993 |page = [https://archive.org/details/nunnsappliedresp0004nunn/page/341 341] |url = https://archive.org/details/nunnsappliedresp0004nunn/page/341 }}</ref> The high cruising altitude also required the use of high pressure oxygen and [[Diving regulator#Demand valve|demand valves]] at the emergency masks unlike the [[Oxygen mask|continuous-flow masks]] used in conventional airliners.{{sfn|Nunn|1993|p=341}} The FAA, which enforces minimum emergency descent rates for aircraft, determined that, in relation to Concorde's higher operating altitude, the best response to a pressure loss incident would be to perform a rapid descent.<ref>{{cite web |url=http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgPolicy.nsf/0/90AA20C2F35901D98625713F0056B1B8?OpenDocument |title=Interim Policy on High Altitude Cabin Decompression – Relevant Past Practice |first=Steve |last=Happenny |publisher=Federal Aviation Administration |date=24 March 2006}}</ref>

The designed operating cabin altitude for new aircraft is falling and this is expected to reduce any remaining physiological problems. Both the [[Boeing 787 Dreamliner]] and the [[Airbus A350 XWB]] airliners have made such modifications for increased passenger comfort. The 787's internal cabin pressure is the equivalent of {{cvt|6000|ft|0}} altitude resulting in a higher pressure than for the {{cvt|8000|ft|0}} altitude of older conventional aircraft;<ref name=breathe>{{cite news |url=https://www.usatoday.com/money/biztravel/2006-10-30-boeing-air-usat_x.htm |work=USA Today |first=Marilyn |last=Adams |title=Breathe easy, Boeing says |date=November 1, 2006}}</ref> according to a joint study performed by Boeing and [[Oklahoma State University]], such a level significantly improves comfort levels.<ref name="Aero_America_200607">{{cite news|url=http://www.aiaa.org/aerospace/images/articleimages/pdf/AA_July05_CRO1.pdf|title=Airbus and Boeing spar for middleweight |publisher=[[American Institute of Aeronautics and Astronautics]] |date=July 2006 |last=Croft |first=John |access-date=July 8, 2007 |archive-url=https://web.archive.org/web/20070710095616/http://www.aiaa.org/aerospace/images/articleimages/pdf/AA_July05_CRO1.pdf |archive-date=July 10, 2007}}</ref><ref name="bca_20040719">{{cite press release |url=http://www.boeing.com/news/releases/2004/q3/nr_040719i.html |title=Boeing 7E7 Offers Preferred Cabin Environment, Study Finds |publisher=Boeing |date=July 19, 2004 |access-date=June 14, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20111106180815/http://www.boeing.com/news/releases/2004/q3/nr_040719i.html |archive-date=November 6, 2011 |df=mdy-all }}</ref> Airbus has stated that the A350 XWB provides for a typical cabin altitude at or below {{cvt|6000|ft|m|0}}, along with a cabin atmosphere of 20% humidity and an airflow management system that adapts cabin airflow to passenger load with draught-free air circulation.<ref name=EADSdec2006>{{cite web |title= Taking the lead: A350XWB presentation |publisher= EADS |date=December 2006 |url= http://www.eads.com/xml/content/OF00000000400004/7/19/41508197.pdf |archive-url= https://web.archive.org/web/20090327094646/http://www.eads.com/xml/content/OF00000000400004/7/19/41508197.pdf |url-status= dead |archive-date= 2009-03-27 }}</ref> The adoption of [[Composite material|composite]] fuselages eliminates the threat posed by [[metal fatigue]] that would have been exacerbated by the higher cabin pressures being adopted by modern airliners, it also eliminates the risk of corrosion from the use of greater humidity levels.<ref name=breathe/>