Editing Cabin pressurization (section)

===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 {{cvt|8000|ft|0}}. 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}}

[[File:Cabin or differential pressure indicator.png|thumb|Pilots can use a "cabin altimeter" (also known as a cabin differential pressure gauge) to measure the difference between inside and outside pressure.<ref>{{Cite PHAK|year=2016|chapter=7|page=36}}</ref>]]

Keeping the cabin altitude below {{cvt|8000|ft|0}} generally prevents significant [[Hypoxic hypoxia|hypoxia]], [[altitude sickness]], [[decompression sickness]], and [[barotrauma]].<ref>{{cite book |url= https://www.iata.org/publications/Documents/medical-manual.pdf |title=Medical Manual 9th Edition| isbn =978-92-9229-445-8 |publisher=International Air Transport Association.}}</ref> [[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.<ref>{{cite journal|pmc=1790988|title=Commercial aircraft cabin altitude|journal=Journal of the Royal Society of Medicine|volume=100|issue=2|page=64|author=Bagshaw M|year=2007|doi=10.1177/014107680710000207|pmid=17277266}}</ref> 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 {{cvt|7000|ft|0}} when cruising at {{cvt|37000|ft|0}}.<ref>{{cite web|url=http://www.boeing.com/commercial/cabinair/ecs.pdf|title=Commercial Airliner Environmental Control System: Engineering Aspects of Cabin Air Quality|url-status=dead|archive-url=https://web.archive.org/web/20110524110211/http://www.boeing.com/commercial/cabinair/ecs.pdf|archive-date=2011-05-24}}</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 {{cvt|4500|ft|0}} when cruising at {{cvt|41000|ft|0}}.<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|access-date=2012-01-09|archive-date=2010-02-16|archive-url=https://web.archive.org/web/20100216040849/http://www2.bombardier.com/en/3_0/3_2/pdf/global_express_xrs_factsheet.pdf|url-status=dead}}</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 {{cvt|41000|ft|0}}.<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>{{Unreliable source?|reason=domain on WP:BLACKLIST|date=July 2016}} One study of eight flights in [[Airbus A380]] aircraft found a median cabin pressure altitude of {{cvt|6128|ft}}, and 65 flights in [[Boeing 747-400]] aircraft found a median cabin pressure altitude of {{cvt|5159|ft}}.<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 assigned a type certificate to fly up to {{cvt|45000|ft|0}} 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 {{cvt|25000|ft|0}} "must be designed so that occupants will not be exposed to cabin pressure altitudes in excess of {{cvt|15000|ft|0}} 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 that 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 {{cvt|25000|ft|0}} for more than 2 minutes, nor to an altitude exceeding {{cvt|40000|ft|0}} 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 {{cvt|40000|ft}} 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/$FILE/8695.doc|title=Exemption No. 8695|publisher=[[Federal Aviation Administration]]|date=2006-03-24|location=Renton, Washington|access-date=2008-10-02|archive-date=2009-03-27|archive-url=https://web.archive.org/web/20090327094608/http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgEX.nsf/0/9929ce16709cad0f8625713f00551e74/$FILE/8695.doc|url-status=dead}}</ref><ref>{{cite web|url=http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgPolicy.nsf/0/90AA20C2F35901D98625713F0056B1B8?OpenDocument|publisher=[[Federal Aviation Administration]]|date=2006-03-24|title=PS-ANM-03-112-16|access-date=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 {{cvt|43000|ft|0}} in the event of a decompression incident and to exceed {{cvt|40,000|ft|0}} for one minute. This allows the A380 to operate at a higher altitude than other newly designed civilian aircraft.<ref name="Exemption No. 8695"/>