Examine individual changes

'{{redirects|Cabin pressure||Cabin Pressure (disambiguation)}} [[File:Pxctl.jpg|thumbnail|right|The pressurization controls on a [[Boeing 737-800]]]] '''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 passengers and crew 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 if necessary, before it is distributed to the cabin by one or more [[Environmental control system (aircraft)|environmental control systems]].<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 | accessdate=December 31, 2012 | author=Brain, Marshall}}</ref> The cabin pressure is regulated by the outflow valve. ==Need for cabin pressurization== Pressurization becomes necessary at altitudes above {{convert|12500|ft|m}} to {{convert|14000|ft|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. It also serves to generally increase passenger comfort and is a regulatory requirement above {{convert|8000|ft|m}}. The principal physiological problems are listed below. Pressurization of the cargo hold is also required to prevent damage to pressure-sensitive goods that might leak, expand, burst or be crushed on re-pressurization. ; [[Hypoxia (medical)|Hypoxia]] : The lower [[partial pressure]] of oxygen at altitude reduces the [[Pulmonary alveolus|alveolar]] oxygen tension in the lungs and subsequently in the brain, leading to sluggish thinking, dimmed vision, loss of consciousness, and ultimately death. In some individuals, particularly those with heart or lung disease, symptoms may begin as low as {{convert|5000|ft|m}}, although most passengers can tolerate altitudes of {{convert|8000|ft|m}} without ill effect. At this altitude, there is about 25% less oxygen than there is at sea level.<ref name="02_calc">{{cite web | author=K. Baillie and A. Simpson | title=Altitude oxygen calculator | url=http://www.altitude.org/air_pressure.php | accessdate=2006-08-13}} - Online interactive altitude oxygen calculator</ref> : Hypoxia may be addressed by the administration of supplemental oxygen, either through an [[oxygen mask]] or through a [[nasal cannula]]. Without pressurization, sufficient oxygen can be delivered up to an altitude of about {{convert|40000|ft|m}}. This is because a person who is used to living at sea level needs about 0.20&nbsp;[[Bar (unit)|bar]] [[Partial pressure of oxygen|partial oxygen pressure]] to function normally and that pressure can be maintained up to about {{convert|40000|ft|m}} by increasing the [[mole fraction]] of oxygen in the air that is being breathed. At {{convert|40000|ft|m}}, the ambient air pressure falls to about 0.2 bar, at which maintaining a minimum partial pressure of oxygen of 0.2 bar requires breathing 100% oxygen using an [[oxygen mask]]. : Emergency oxygen supply masks in the passenger compartment of airliners do not need to be [[oxygen masks|pressure-demand masks]] because most flights stay below {{convert|40000|ft|m}}. Above that altitude the partial pressure of oxygen will fall below 0.2 bar even at 100% oxygen and some degree of cabin pressurization or rapid descent will be essential to avoid the risk of hypoxia. ; [[Altitude sickness]] : [[Hyperventilation]], the body’s most common response to hypoxia, does help to partially restore the partial pressure of oxygen in the blood, but it also causes [[carbon dioxide]] (CO₂) to out-gas, raising the blood pH and inducing [[alkalosis]]. Passengers may experience fatigue, [[nausea]], headaches, sleeplessness, and (on extended flights) even [[pulmonary oedema]]. These are the same symptoms that mountain climbers experience, but the limited duration of powered flight makes the development of pulmonary oedema unlikely. Altitude sickness may be controlled by a full [[pressure suit]] with helmet and faceplate, which completely envelops the body in a pressurized environment; however, this is impractical for commercial passengers. ; [[Decompression sickness]] : The low partial pressure of gases, principally nitrogen (N₂) but including all other gases, may cause dissolved gases in the bloodstream to precipitate out, resulting in ''gas embolism,'' or bubbles in the bloodstream. The mechanism is the same as that of compressed-air divers on ascent from depth. Symptoms may include the early symptoms of "the bends"—tiredness, forgetfulness, headache, stroke, thrombosis, and subcutaneous itching—but rarely the full symptoms thereof. Decompression sickness may also be controlled by a full-pressure suit as for altitude sickness. ; [[Barotrauma]] : As the aircraft climbs or descends, passengers may experience discomfort or acute pain as gases trapped within their bodies expand or contract. The most common problems occur with air trapped in the [[middle ear]] (aerotitus) or paranasal sinuses by a blocked Eustachian tube or sinuses. Pain may also be experienced in the [[Human gastrointestinal tract|gastrointestinal tract]] or even the teeth ([[barodontalgia]]). Usually these are not severe enough to cause actual trauma but can result in soreness in the ear that persists after the flight and can exacerbate or precipitate pre-existing medical conditions, such as [[pneumothorax]]. ==Cabin altitude== [[File:Empty bottle crushed by cabin pressurization.jpg|upright|thumb|An empty bottle, closed during a commercial flight with a cabin altitude of around 8,000 ft, is crushed by the pressure at ground level after descent.]] The pressure inside the cabin is technically referred to as the ''equivalent effective cabin altitude'' or more commonly as the ''cabin altitude''. This is defined as the equivalent altitude above [[sea level|mean sea level]] having the same [[atmospheric pressure]] according to a standard atmospheric model such as the [[International Standard Atmosphere]]. Thus a cabin altitude of zero would have the pressure found at mean sea level, which is taken to be {{convert|101325|Pa|psi|sigfig=5}}.<ref name="aeromech.usyd.edu.au">{{Cite web | last = Auld | first = D.J. | last2 = Srinivas | first2 = K. | title = Properties of the Atmosphere | date = 2008 | url = http://www.aeromech.usyd.edu.au/aero/atmosphere/ | accessdate = 2008-03-13 | postscript = <!--None--> }}</ref> ===Aircraft=== In [[airliner]]s, cabin altitude during flight is kept above sea level in order to reduce stress on the pressurized part of the [[fuselage]]; this stress is proportional to the difference in pressure inside and outside the cabin. In a typical commercial passenger flight, the cabin altitude is programmed to rise gradually from the altitude of the airport of origin to a regulatory maximum of {{convert|8000|ft|m|abbr=on}}. This cabin altitude is maintained while the aircraft is cruising at its maximum altitude and then reduced gradually during descent until the cabin pressure matches the ambient air pressure at the destination.{{citation needed|date=May 2015}} Keeping the cabin altitude below {{convert|8000|ft|m|abbr=on}} generally prevents significant [[Hypoxic hypoxia|hypoxia]], [[altitude sickness]], [[decompression sickness]], and [[barotrauma]].{{citation needed|date=May 2015}} [[Federal Aviation Administration]] (FAA) regulations in the U.S. mandate that under normal operating conditions, the cabin altitude may not exceed this limit at the maximum operating altitude of the aircraft.{{citation needed|date=May 2015}} This mandatory maximum cabin altitude does not eliminate all physiological problems; passengers with conditions such as [[pneumothorax]] are advised not to fly until fully healed, and people suffering from a cold or other infection may still experience pain in the ears and sinuses.{{citation needed|date=May 2015}} The rate of change of cabin altitude strongly affects comfort as humans are sensitive to pressure changes in the [[inner ear]] and [[Paranasal sinuses|sinuses]] and this has to be managed carefully. [[Scuba diving|Scuba]] divers flying within the "no fly" period after a dive are at risk of [[decompression sickness]] because the accumulated nitrogen in their bodies can form bubbles when exposed to reduced cabin pressure. The cabin altitude of the [[Boeing 767]] is typically about {{convert|6900|ft|m}} when cruising at {{convert|39000|ft|m}}.<ref>{{cite web |url=http://www.boeing.com/commercial/cabinair/ecs.pdf|title=Commercial Airliner Environmental Control System: Engineering Aspects of Cabin Air Quality}}</ref> This is typical for older jet airliners. A design goal for many, but not all, newer aircraft is to provide a lower cabin altitude than older designs. This can be beneficial for passenger comfort.<ref name="flightglobal">{{cite web|url=http://www.flightglobal.com/news/articles/in-focus-manufacturers-aim-for-more-comfortable-cabin-climate-369425/|title=Manufacturers aim for more comfortable cabin climate|publisher=Flightglobal|date=19 Mar 2012 }}</ref> For example, the [[Bombardier Global Express]] business jet can provide a cabin altitude of {{convert|4500|ft|m|abbr=on|sigfig=2}} when cruising at {{convert|41000|ft|m}}.<ref name=xrs>{{cite web |url= http://www.aero-news.net/index.cfm?do=main.textpost&id=293b270c-653f-4b6a-84b8-e3f9b4754dc5 |title=Bombardier's Stretching Range on Global Express Global Express XRS|work=Aero-News Network |date=October 7, 2003}}</ref><ref name=bombardier>{{cite web|url=http://www2.bombardier.com/en/3_0/3_2/pdf/global_express_xrs_factsheet.pdf|title=Bombardier Global Express XRS Factsheet|publisher=Bombardier|year=2011}}</ref><ref name=ecs>{{cite web|url=http://www.srs.aero/wordpress/wp-content/uploads/2010/11/AERO-4003-ECS-Lecture-Final.pdf|title=Aircraft Environmental Control Systems|publisher=Carleton University|year=2003}}</ref> The [[Emivest SJ30]] business jet can provide a sea-level cabin altitude when cruising at {{convert|41000|ft|m}}.<ref>[http://www.flightglobal.com/news/articles/flight-test-emivest-sj30-long-range-rocket-333285/ FLIGHT TEST: Emivest SJ30 - Long-range rocket] Retrieved 27 September 2012.</ref><ref>[http://www.aerospace-technology.com/projects/sj30-2/ SJ30-2, United States of America] Retrieved 27 September 2012.</ref> One study of 8 flights in [[Airbus A380]] aircraft found a median cabin pressure altitude of {{convert|6128|ft|m}}, and 65 flights in [[Boeing 747-400]] aircraft found a median cabin pressure altitude of {{convert|5159|ft|m}}.<ref name=ers>{{cite web |url= http://www.ersnet.org/index.php?option=com_flexicontent&view=items&id=4106:airlines-are-cu |title=Airlines are cutting costs – Are patients with respiratory diseases paying the price?|work=European Respiratory Society |year=2010}}</ref> Before 1996, approximately 6,000 large commercial transport airplanes were type-certificated to fly up to {{convert|45000|ft|m|abbr=on}} without having to meet high-altitude special conditions.<ref>{{cite web|url=http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgPolicy.nsf/0/90AA20C2F35901D98625713F0056B1B8?OpenDocument|title=Final Policy FAR Part 25 Sec. 25.841 07/05/1996&#124;Attachment 4}}</ref> In 1996, the FAA adopted Amendment 25-87, which imposed additional high-altitude cabin pressure specifications for new-type aircraft designs. Aircraft certified to operate above {{convert|25000|ft|m|abbr=on}} "must be designed so that occupants will not be exposed to cabin pressure altitudes in excess of {{convert|15000|ft|m|abbr=on}} after any probable failure condition in the pressurization system".<ref name="FARs, 14 CFR, Part 25, Section 841">{{cite web|url=http://www.flightsimaviation.com/data/FARS/part_25-841.html|title=FARs, 14 CFR, Part 25, Section 841}}</ref> In the event of a decompression which results from "any failure condition not shown to be extremely improbable", the plane must be designed such that occupants will not be exposed to a cabin altitude exceeding {{convert|25000|ft|m|abbr=on}} for more than 2 minutes, nor to an altitude exceeding {{convert|40000|ft|m|abbr=on}} at any time.<ref name="FARs, 14 CFR, Part 25, Section 841"/> In practice, that new [[Federal Aviation Regulations]] amendment imposes an operational [[Ceiling (aeronautics)|ceiling]] of {{convert|40000|ft|m|abbr=on}} on the majority of newly designed commercial aircraft.<ref name="Exemption No. 8695">{{cite web|url=http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgEX.nsf/0/9929ce16709cad0f8625713f00551e74/$FILE/8695.doc|title=Exemption No. 8695|publisher=[[Federal Aviation Authority]]|date=2006-03-24|location=Renton, Washington|accessdate=2008-10-02}}</ref><ref>{{cite web|url=http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgPolicy.nsf/0/90AA20C2F35901D98625713F0056B1B8?OpenDocument|publisher=[[Federal Aviation Authority]]|date=2006-03-24|title=PS-ANM-03-112-16|accessdate=2009-09-23|author=Steve Happenny}}</ref> Aircraft manufacturers can apply for a relaxation of this rule if the circumstances warrant it. In 2004, [[Airbus]] acquired an FAA exemption to allow the cabin altitude of the A380 to reach {{Convert|43,000|ft|m|abbr=on}} in the event of a decompression incident and to exceed {{Convert|40,000|ft|m|abbr=on}} for one minute. This allows the A380 to operate at a higher altitude than other newly designed civilian aircraft.<ref name="Exemption No. 8695"/> ===Spacecraft=== Russian engineers have chosen to use an air-like nitrogen/oxygen mixture, kept at a cabin altitude near zero at all times, in their 1961 [[Vostok (spacecraft)|Vostok]], 1964 [[Voskhod (spacecraft)|Voskhod]], and 1967 to present [[Soyuz (spacecraft)|Soyuz]] spacecraft.<ref>{{cite book | last = Gatland | first = Kenneth | authorlink = | title = Manned Spacecraft | publisher = MacMillan | edition = Second | date = 1976 | location = New York | pages = 256 | isbn = | jfm = }} </ref> This requires a heavier [[space vehicle]] design, because the spacecraft cabin structure must withstand the stress of 14.7 pounds per square inch (1 bar) against the vacuum of space, and also because an inert nitrogen mass must be carried. Care must also be taken to avoid [[decompression sickness]] when cosmonauts perform [[extravehicular activity]], as current soft [[space suit]]s are pressurized with pure oxygen at relatively low pressure in order to provide reasonable flexibility.<ref>Gatland, p. 134</ref> By contrast, the United States chose to use a pure oxygen atmosphere for its 1961 [[Project Mercury|Mercury]], 1965 [[Project Gemini|Gemini]], and 1967 [[Apollo spacecraft|Apollo]] spacecraft, mainly in order to avoid decompression sickness.<ref>{{cite book|last=Catchpole|first=John|title=Project Mercury - NASA's First Manned Space Programme|year=2001|publisher=Springer Praxis|location=Chichester, UK|isbn=1-85233-406-1|page=410}}</ref><ref>{{cite journal |last=Giblin |first=Kelly A. |date=Spring 1998 |title ='Fire in the Cockpit!' |journal=[[American Heritage of Invention & Technology]] |volume=13 |issue=4 |publisher=American Heritage Publishing |url=http://www.americanheritage.com/articles/magazine/it/1998/4/1998_4_46.shtml |archiveurl=http://web.archive.org/web/20081120153024/http://www.americanheritage.com/articles/magazine/it/1998/4/1998_4_46.shtml |archivedate=November 20, 2008 |accessdate=March 23, 2011}}</ref> Mercury used a cabin altitude of {{convert|24800|ft|m}} ({{convert|5.5|psi|bar}});<ref>Gatland, p. 264</ref> Gemini used an altitude of {{convert|25700|ft|m}} ({{convert|5.3|psi|bar}});<ref>Gatland, p. 269</ref> and Apollo used {{convert|27000|ft|m}} ({{convert|5.0|psi|bar}})<ref>Gatland, p. 278,284</ref> in space. This allowed for a lighter space vehicle design. Before launch, the pressure was kept at slightly higher than sea level (a constant {{convert|5.3|psi|bar}} above ambient for Gemini, and {{convert|2|psi|bar}} above sea level at launch for Apollo), and transitioned to the space cabin altitude during ascent. However, the high pressure pure oxygen atmosphere proved to be a fatal fire hazard in Apollo, contributing to the deaths of the entire crew of [[Apollo 1]] during a 1967 ground test. After this, [[NASA]] revised its procedure to use a 40% nitrogen/60% oxygen mix at zero cabin altitude at launch, but kept the low-pressure pure oxygen in space. After Apollo, the United States chose to use air-like cabin atmospheres for its [[Skylab]]{{citation needed|date=December 2015}}, [[Space Shuttle]]{{citation needed|date=December 2015}}, and the [[International Space Station]]{{clarify|date=December 2015}}{{citation needed|date=December 2015}}. ==Mechanics== Pressurization is achieved by the design of an airtight fuselage engineered to be pressurized with a source of compressed air and controlled by an [[environmental control system]] (ECS). The most common source of compressed air for pressurization is [[bleed air]] extracted from the compressor stage of a [[gas turbine]] engine, from a low or intermediate stage and also from an additional high stage; the exact stage can vary depending on engine type. By the time the cold outside air has reached the bleed air valves, it is at a very high pressure and has been heated to around {{convert|200|°C|°F|abbr=on|lk=on}}. The control and selection of high or low bleed sources is fully automatic and is governed by the needs of various pneumatic systems at various stages of flight.<ref name="Engineering Aspects of Cabin Air">{{cite web |url=http://www.cabinfiles.com/?CFrequest=file;03032001100119 Commercial Airliner Environmental Control System|title=Engineering Aspects of Cabin Air}}</ref> The part of the bleed air that is directed to the ECS is then expanded and cooled to a suitable temperature by passing it through a [[heat exchanger]] and [[air cycle machine]] known as the packs system. In some larger airliners, hot trim air can be added downstream of air conditioned air coming from the packs if it is needed to warm a section of the cabin that is colder than others. [[File:Outflow.jpg|thumb|left|Outflow and pressure relief valve on a [[Boeing 737 Next Generation|Boeing 737-800]]]] At least two engines provide compressed bleed air for all the plane's pneumatic systems, to provide full [[Redundancy (engineering)|redundancy]]. Compressed air is also obtained from the [[auxiliary power unit]] (APU), if fitted, in the event of an emergency and for cabin air supply on the ground before the main engines are started. Most modern commercial aircraft today have fully redundant, duplicated electronic controllers for maintaining pressurization along with a manual back-up control system. All exhaust air is dumped to atmosphere via an outflow valve, usually at the rear of the fuselage. This valve controls the cabin pressure and also acts as a safety relief valve, in addition to other safety relief valves. If the automatic pressure controllers fail, the pilot can manually control the cabin pressure valve, according to the backup emergency procedure checklist. The automatic controller normally maintains the proper cabin pressure altitude by constantly adjusting the outflow valve position so that the cabin altitude is as low as practical without exceeding the maximum pressure differential limit on the fuselage. The pressure differential varies between aircraft types, typical values are between {{convert|7.8|psi|kPa|abbr=on|lk=on}} and {{convert|9.4|psi|kPa|abbr=on|lk=on}}.<ref name="Differential Pressure Characteristics of Aircraft">{{cite web |url=http://mrcabinpressure.com/aircraft.htm|title=Differential Pressure Characteristics of Aircraft}}</ref> At {{convert|39000|ft|m}}, the cabin pressure would be automatically maintained at about {{convert|6900|ft|m}} ({{convert|450|ft|m}} lower than Mexico City), which is about {{convert|11.5|psi|kPa|abbr=on}} of atmosphere pressure.<ref name="Engineering Aspects of Cabin Air"/> Some aircraft, such as the [[Boeing 787 Dreamliner]], have re-introduced electric compressors previously used on piston-engined airliners to provide pressurization.<ref name="AERO_QTR_406_787_from_the_ground_up">[http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_06/AERO_Q406_article4.pdf "Boeing 787 from the Ground Up"]</ref> The use of electric compressors increases the electrical generation load on the engines and introduces a number of stages of energy transfer; therefore, it is unclear whether this increases the overall efficiency of the aircraft air handling system. It does, however, remove the danger of [[Fume event|chemical contamination of the cabin]], simplify engine design, avert the need to run high pressure pipework around the aircraft, and provide greater design flexibility. ==Unplanned decompression== {{Main|Uncontrolled decompression}} [[File:Passenger oxygen mask dsc06035.jpg|thumb|upright|Passenger oxygen mask deployment]] Unplanned loss of cabin pressure at altitude is rare but has resulted in a [[Uncontrolled decompression#Notable decompression accidents and incidents|number of fatal accidents]]. Failures range from sudden, catastrophic loss of airframe integrity (explosive decompression) to slow leaks or equipment malfunctions that allow cabin pressure to drop undetected to levels that can lead to unconsciousness or severe performance degradation of the aircrew. Any failure of cabin pressurization above {{convert|10000|ft|m}} requires an emergency descent to {{convert|8000|ft|m}} or the closest to that while maintaining the Minimum Safe Altitude (MSA), and the deployment of an [[oxygen mask]] for each seat. The oxygen systems have sufficient oxygen for all on board and give the pilots adequate time to descend to below {{convert|8000|ft|m|abbr=on}}. Without emergency oxygen, [[Hypoxia (medical)|hypoxia]] may lead to loss of consciousness and a subsequent loss of control of the aircraft. The [[time of useful consciousness]] varies according to altitude. As the pressure falls the cabin air temperature may also plummet to the ambient outside temperature with a danger of [[hypothermia]] or [[frostbite]]. In [[jet fighter]] aircraft, the small size of the [[cockpit]] means that any decompression will be very rapid and would not allow the pilot time to put on an oxygen mask. Therefore, fighter jet pilots and aircrew are required to wear oxygen masks at all times.<ref>{{cite web |url=http://goflightmedicine.com/hypoxia/ |title=Hypoxia |last1=Jedick MD/MBA |first1=Rocky |last2= |first2= |date=28 April 2013 |website=goflightmedicine.com |publisher=Go Flight Medicine |accessdate=17 March 2014}}</ref> On June 30, 1971, the crew of [[Soyuz 11]], Soviet cosmonauts [[Georgy Dobrovolsky]], [[Vladislav Volkov]], and [[Viktor Patsayev]] were killed after the cabin vent valve accidentally opened before atmospheric re-entry. There had been no indication of trouble until the recovery team opened the capsule and found the dead crew.<ref name="time">{{cite news|url=http://www.time.com/time/magazine/article/0,9171,903011,00.html|title=Triumph and Tragedy of Soyuz 11|accessdate=20 October 2007|publisher=[[Time (magazine)|Time Magazine]]|author=Time Magazine | date=12 July 1971}}</ref><ref name="ea">{{Cite web|url=http://www.astronautix.com/flights/soyuz11.htm|title=Soyuz 11|accessdate=20 October 2007|publisher=Encyclopedia Astronautica|year=2007|author=Encyclopedia Astronautica}}</ref> ==History== 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) * [[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 pressurised 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, which crashed on first flight) * [[Boeing 307]] (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) * [[SyberJet SJ30]] (2005) First civilian business jet to certify 12.0 psi pressurization system allowing for a sea level cabin at {{convert|41000|ft|m|abbr=on}}. In the late 1910s, attempts were being made to achieve higher and higher altitudes. In 1920, flights well over {{convert|37000|ft|m|abbr=on}} were first achieved by test pilot Lt. [[John A. Macready]] in a [[Packard-Le Père LUSAC-11]] biplane at [[McCook Field]] in [[Dayton, Ohio]].<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=128–129}}</ref> The flight was possible by releasing stored oxygen into the cockpit, which was released directly into an enclosed cabin and not to an oxygen mask, which was developed later.<ref name="Cornelisse"/> With this system flights nearing {{convert|40000|ft|m|abbr=on}} were possible, but the lack of atmospheric pressure at that altitude caused the pilot's heart to enlarge visibly, and many pilots reported health problems from such high altitude flights.<ref name="Cornelisse"/> Some early airliners had oxygen masks for the passengers for routine flights. In 1921, a Wright-Dayton USD-9A reconnaissance biplane was modified with the addition of a completely enclosed air-tight chamber that could be pressurized with air forced into it by small external turbines.<ref name="Cornelisse"/> The chamber had a hatch only {{convert|22|in|m|abbr=on}} in diameter that would be sealed by the pilot at {{convert|3000|ft|m|abbr=on}}.<ref name="Cornelisse"/> The chamber contained only one instrument, an altimeter, while the conventional cockpit instruments were all mounted outside the chamber, visible through five small portholes.<ref name="Cornelisse"/> The first attempt to operate the aircraft was again made by Lt. John A. McCready, who discovered that the turbine was forcing air into the chamber faster than the small release valve provided could release it.<ref name="Cornelisse"/> As a result, the chamber quickly over pressurized, and the flight was abandoned.<ref name="Cornelisse"/> A second attempt had to be abandoned when the pilot discovered at {{convert|3000|ft|m|abbr=on}} that he was too short to close the chamber hatch.<ref name="Cornelisse"/> The first successful flight was finally made by test pilot Lt. Harrold Harris, making it the world's first flight by a pressurized aircraft.<ref name="Cornelisse"/> The first airliner with a pressurized cabin was the [[Boeing 307]] Stratoliner, built in 1938, prior to [[World War II]], though only ten were produced. 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 and this led to the first bomber with cabin pressurization (though restricted to crew areas), the [[Boeing B-29 Superfortress]]. 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= |pages=329–43 |date=August 1966 |doi=10.2307/3636792}}</ref> Post-war piston airliners such as the [[Lockheed Constellation]] (1943) extended the technology to civilian service. The piston engined airliners generally relied on electrical compressors to provide pressurized cabin air. Engine supercharging and cabin pressurization enabled planes like the [[Douglas DC-6]], the [[Douglas DC-7]], and the Constellation to have certified service ceilings from {{convert|24000|ft|m|abbr=on}} to {{convert|28400|ft|m|abbr=on}}. 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 {{convert|30000|-|41000|ft|m|abb=on}} 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 {{convert|36000|ft|m|abbr=on}}. 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|url=http://aerade.cranfield.ac.uk/ara/arc/rm/3248.pdf|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|publisher=Ministry of Aviation|year=1962}}</ref> were applied directly to the design of the [[Boeing 707]] (1957) and all subsequent jet airliners. One immediately 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. 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. [[Concorde]] had to deal with particularly high pressure differentials because it flew at unusually high altitude (up to {{convert|60000|ft|m}}) and maintained a cabin altitude of {{convert|6000|ft|m|abbr=on}}.<ref>Hepburn, A.N. [http://occmed.oxfordjournals.org/cgi/reprint/17/2/47.pdf "Human Factors in the Concord".] ''Occupational Medicine'', 17: 1967, pp. 47–51.</ref> This made the aircraft significantly heavier and contributed to the high cost of a flight. The Concorde also had smaller cabin windows than most other commercial passenger aircraft in order to slow the rate of decompression if a window failed.<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 = 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. The designed operating cabin altitude for new aircraft is falling and this is expected to reduce any remaining physiological problems. ==See also== *[[Aerotoxic syndrome]] *[[Air cycle machine]] *[[Atmosphere (unit)]] *[[Compressed air]] *[[Fume event]] *[[Rarefaction]] *[[Space suit]] *[[Time of useful consciousness]] *[http://sami-aeromedical.com/ Southern AeroMedical Institute], Slow Onset Hypoxia Training and Resource Center for general aviation, commercial, flight attendants, and cadets. ==Footnotes== {{reflist|2}} ==General references== *{{cite journal |author=Seymour L. Chapin |title=Garrett and Pressurized Flight: A Business Built on Thin Air |journal=Pacific Historical Review |volume=35 |issue= |pages=329–43 |date=August 1966 |doi=10.2307/3636792}} *{{cite journal |author=Seymour L. Chapin |title=Patent Interferences and the History of Technology: A High-flying Example |journal=Technology and Culture |volume=12 |issue= 3|pages=414–46 |date=July 1971 |doi=10.2307/3102997 |jstor=3102997}} * Cornelisse, Diana G. Splended Vision, Unswerving Purpose; Developing Air Power for the United States Air Force During the First Century of Powered Flight. Wright-Patterson Air Force Base, Ohio: U.S. Air Force Publications, 2002. ISBN 0-16-067599-5. pp.&nbsp;128–129. *Portions from the [http://www.vnh.org/FSManual/01/07RapidDecompress.html United States Naval Flight Surgeon's Manual] *[http://www.cnn.com/2005/WORLD/europe/08/14/greece.crash/index.html CNN: 121 Dead in Greek Air Crash] ==External Links== * {{YouTube|UhR0p0ZVKvE|Video with Cabin Pressurization Demo in Civil Aircraft}} {{Authority control}} {{DEFAULTSORT:Cabin Pressurization}} [[Category:Aerospace engineering]] [[Category:Pressure vessels]] [[Category:Aviation safety]] [[ja:与圧#航空機]]'