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Cabin doors are designed to make it nearly impossible to lose pressurization through opening a cabin door in flight, either accidentally or intentionally. The [[plug door]] design ensures that when the pressure inside the cabin exceeds the pressure outside, the doors are forced shut and will not open until the pressure is equalized. Cabin doors, including the emergency exits, but not all cargo doors, open inwards, or must first be pulled inwards and then rotated before they can be pushed out through the door frame because at least one dimension of the door is larger than the door frame. Pressurization prevented the doors of [[Saudia Flight 163]] from being opened on the ground after the aircraft made a successful emergency landing, resulting in the deaths of all 287 passengers and 14 crew members from fire and smoke.
Prior to 1996, approximately 6,000 large commercial transport airplanes were [[type certificate|type certified]] to fly up to {{convert|45000|ft}}, without being required to meet special conditions related to flight at high altitude.<ref>{{Cite web|url=https://rgl.faa.gov/|title=RGL Home Page|website=rgl.faa.gov|access-date=2022-11-06|archive-date=2022-12-14|archive-url=https://web.archive.org/web/20221214143433/https://rgl.faa.gov/|url-status=dead}}</ref> In 1996, the FAA adopted Amendment 25–87, which imposed additional high-altitude cabin-pressure specifications, for new designs of aircraft types.<ref name="FAA_25.841">{{cite web|url=http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/0/FED94F31539484AB852566720051AA5D?OpenDocument|title=Section 25.841: Airworthiness Standards: Transport Category Airplanes|publisher=[[Federal Aviation Administration]]|date=1996-05-07|access-date=2008-10-02|archive-date=2009-02-02|archive-url=https://web.archive.org/web/20090202140424/http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/0/FED94F31539484AB852566720051AA5D?OpenDocument|url-status=dead}}</ref> For aircraft [[type certificate|certified]] to operate above 25,000 feet (FL 250; 7,600 m), it "must be designed so that occupants will not be exposed to cabin pressure altitudes in excess of {{convert|15000|ft}} 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=Flightsim Aviation Zone - Number 1 Flight Simulation & Aviation Resource! - Flight Simulator, Aviation Databases|website=www.flightsimaviation.com}}</ref> In the event of a decompression which results from "any failure condition not shown to be extremely improbable," the aircraft must be designed so that occupants will not be exposed to a cabin altitude exceeding {{convert|25000|ft}} for more than 2 minutes, nor exceeding an altitude of {{convert|40000|ft}} at any time.<ref name="FARs, 14 CFR, Part 25, Section 841"/> In practice, that new FAR amendment imposes an operational [[Ceiling (aeronautics)|ceiling]] of 40,000 feet 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><ref group="Note">Notable exceptions include the [[Airbus A380]], [[Boeing 787]], and [[Concorde]]</ref>
In 2004, [[Airbus]] successfully petitioned the FAA to allow cabin pressure of the [[Airbus A380|A380]] to reach {{convert|43000|ft}} in the event of a decompression incident and to exceed {{convert|40000|ft}} for one minute. This special exemption allows the A380 to operate at a higher altitude than other newly designed civilian aircraft, which have not yet been granted a similar exemption.<ref name="Exemption No. 8695"/>
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