Uncontrolled decompression

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An uncontrolled decompression is an undesired drop in the pressure of a sealed system, such as a pressurised aircraft cabin or hyperbaric chamber, that typically results from human error, structural failure, or impact, causing the pressurised vessel to vent into its surroundings or fail to pressurize at all.

Contents

Such decompression may be classed as explosive, rapid, or slow:

Description

In this test chamber, air pressure drops suddenly to that of the atmosphere at 60,000 ft (18,000 m). Air humidity immediately condenses into fog, which within seconds evaporates back into gas. Explosive Decompression Test System.gif
In this test chamber, air pressure drops suddenly to that of the atmosphere at 60,000 ft (18,000 m). Air humidity immediately condenses into fog, which within seconds evaporates back into gas.

The term uncontrolled decompression here refers to the unplanned depressurisation of vessels that are occupied by people; for example, a pressurised aircraft cabin at high altitude, a spacecraft, or a hyperbaric chamber. For the catastrophic failure of other pressure vessels used to contain gas, liquids, or reactants under pressure, the term explosion is more commonly used, or other specialised terms such as BLEVE may apply to particular situations.

Decompression can occur due to structural failure of the pressure vessel, or failure of the compression system itself. [1] [2] The speed and violence of the decompression is affected by the size of the pressure vessel, the differential pressure between the inside and outside of the vessel, and the size of the leak hole.

The US Federal Aviation Administration recognizes three distinct types of decompression events in aircraft: explosive, rapid, and gradual decompression. [1] [2]

Explosive decompression

Explosive decompression occurs typically in less than 0.1 to 0.5 seconds, a change in cabin pressure faster than the lungs can decompress. [1] [3] Normally, the time required to release air from the lungs without restrictions, such as masks, is 0.2 seconds. [4] The risk of lung trauma is very high, as is the danger from any unsecured objects that can become projectiles because of the explosive force, which may be likened to a bomb detonation.

Immediately after an explosive decompression, a heavy fog may fill the aircraft cabin as the air cools, raising the relative humidity and causing sudden condensation. [4] Military pilots with oxygen masks must pressure-breathe, whereby the lungs fill with air when relaxed, and effort has to be exerted to expel the air again. [5]

Rapid decompression

Rapid decompression typically takes more than 0.1 to 0.5 seconds, allowing the lungs to decompress more quickly than the cabin. [1] [6] The risk of lung damage is still present, but significantly reduced compared with explosive decompression.

Gradual decompression

Slow, or gradual, decompression occurs slowly enough to go unnoticed and might only be detected by instruments. [7] This type of decompression may also come about from a failure to cabin pressurization as an aircraft climbs to altitude. An example of this is the 2005 Helios Airways Flight 522 crash, in which the maintenance service left the pressurization system in manual mode and the pilots did not check the pressurization system. As a result, they suffered a loss of consciousness (as well as most of the passengers and crew) due to hypoxia (lack of oxygen). The plane continued to fly due to the autopilot system and eventually crashed due to fuel exhaustion after leaving its flight path.

Decompression injuries

NASA astronaut candidates being monitored for signs of hypoxia during training in an altitude chamber US Navy 091006-N-9001B-017 Hospital Corpsmen 2nd Class Kyle Carswell and Daniel Young monitor members of the 2009 class of NASA astronaut candidates for hypoxia in an altitude chamber.jpg
NASA astronaut candidates being monitored for signs of hypoxia during training in an altitude chamber

The following physical injuries may be associated with decompression incidents:

At least two confirmed cases have been documented of a person being blown through an airplane passenger window. The first occurred in 1973 when debris from an engine failure struck a window roughly midway in the fuselage. Despite efforts to pull the passenger back into the airplane, the occupant was forced entirely through the cabin window. [15] The passenger's skeletal remains were eventually found by a construction crew, and were positively identified two years later. [16] The second incident occurred on April 17, 2018, when a woman on Southwest Airlines Flight 1380 was partially blown through an airplane passenger window that had broken from a similar engine failure. Although the other passengers were able to pull her back inside, she later died from her injuries. [17] [18] [19] In both incidents, the plane landed safely with the sole fatality being the person seated next to the window involved.

According to NASA scientist Geoffrey A. Landis, the effect depends on the size of the hole, which can be expanded by debris that is blown through it; "it would take about 100 seconds for pressure to equalise through a roughly 30.0 cm (11.8 in) hole in the fuselage of a Boeing 747." Anyone blocking the hole would have half a ton of force pushing them towards it, but this force reduces rapidly with distance from the hole. [20]

Implications for aircraft design

Modern aircraft are specifically designed with longitudinal and circumferential reinforcing ribs in order to prevent localised damage from tearing the whole fuselage open during a decompression incident. [21] However, decompression events have nevertheless proved fatal for aircraft in other ways. In 1974, explosive decompression onboard Turkish Airlines Flight 981 caused the floor to collapse, severing vital flight control cables in the process. The FAA issued an Airworthiness Directive the following year requiring manufacturers of wide-body aircraft to strengthen floors so that they could withstand the effects of in-flight decompression caused by an opening of up to 20 square feet (1.9 m2) in the lower deck cargo compartment. [22] Manufacturers were able to comply with the Directive either by strengthening the floors and/or installing relief vents called "dado panels" between the passenger cabin and the cargo compartment. [23]

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 certified to fly up to 45,000 feet (14,000 m), without being required to meet special conditions related to flight at high altitude. [24] In 1996, the FAA adopted Amendment 25–87, which imposed additional high-altitude cabin-pressure specifications, for new designs of aircraft types. [25] For aircraft 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 15,000 feet (4,600 m) after any probable failure condition in the pressurization system." [26] 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 25,000 feet (7,600 m) for more than 2 minutes, nor exceeding an altitude of 40,000 feet (12,000 m) at any time. [26] In practice, that new FAR amendment imposes an operational ceiling of 40,000 feet on the majority of newly designed commercial aircraft. [27] [28] [Note 1]

In 2004, Airbus successfully petitioned the FAA to allow cabin pressure of the A380 to reach 43,000 feet (13,000 m) in the event of a decompression incident and to exceed 40,000 feet (12,000 m) 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. [27]

International standards

The Depressurization Exposure Integral (DEI) is a quantitative model that is used by the FAA to enforce compliance with decompression-related design directives. The model relies on the fact that the pressure that the subject is exposed to and the duration of that exposure are the two most important variables at play in a decompression event. [29]

Other national and international standards for explosive decompression testing include:

Notable decompression accidents and incidents

Decompression incidents are not uncommon on military and civilian aircraft, with approximately 40–50 rapid decompression events occurring worldwide annually. [30] However, in most cases the problem is manageable, injuries or structural damage rare and the incident not considered notable. [8] One notable, recent case was Southwest Airlines Flight 1380 in 2018, where an uncontained engine failure ruptured a window, causing a passenger to be partially blown out. [31]

Decompression incidents do not occur solely in aircraft; the Byford Dolphin accident is an example of violent explosive decompression of a saturation diving system on an oil rig. A decompression event is often the result of a failure caused by another problem (such as an explosion or mid-air collision), but the decompression event may worsen the initial issue.

EventDatePressure vesselEvent typeFatalities/number on boardDecompression typeCause
Pan Am Flight 2011952 Boeing 377 Stratocruiser Accident1/27Explosive decompressionPassenger door blew out after lock failure [32]
BOAC Flight 781 1954 de Havilland Comet 1 AccidentExplosive decompressionMetal fatigue
South African Airways Flight 201 1954 de Havilland Comet 1 AccidentExplosive decompression [33] Metal fatigue
TWA Flight 2 1956 Lockheed L-1049 Super Constellation AccidentExplosive decompression Mid-air collision
American Airlines Flight 871957 Douglas DC-7 Accident0/46Explosive decompressionPropeller blade separated and hit fuselage [34]
Air France F-BGNE1957 Lockheed Super Constellation AccidentExplosive decompressionWindow shattered at 18,000 feet (5,500 m) [35]
Continental Airlines Flight 11 1962 Boeing 707-100 BombingExplosive decompressionInsurance fraud suicide bomb
Aerolineas Argentinas Flight 7371962 Avro 748-105 Srs. 1 Accident1/34Explosive decompressionAft left passenger door separated from airplane [36]
Volsk parachute jump accident 1962 Pressure suit AccidentRapid decompressionCollision with gondola upon jumping from balloon
Cambrian Airways G-AMON1964 Vickers 701 Viscount Accident0/63Explosive decompressionPropeller blade separated and hit fuselage [37]
Strato Jump III 1966Pressure suitAccidentRapid decompressionPressure suit failure [38]
Apollo program spacesuit testing accident1966 Apollo A7L spacesuit (or possibly a prototype of it)AccidentRapid decompressionOxygen line coupling failure [39]
Northeast Airlines N8224H1967 Douglas DC-6B Accident0/14Explosive decompressionFuselage cracked open from fatigue [40]
USAF 59-05301970 Douglas C-133B Cargomaster Accident5/5Explosive decompressionExisting crack expanded, leading to fuselage failure [41]
Hughes Airwest Flight 706 1971 McDonnell Douglas DC-9-31 AccidentExplosive decompressionMid-air Collision
Soyuz 11 re-entry 1971 Soyuz spacecraft AccidentRapid decompressionPressure equalisation valve damaged by faulty pyrotechnic separation charges [42]
BEA Flight 706 1971 Vickers Vanguard AccidentExplosive decompressionStructural failure of rear pressure bulkhead due to corrosion
JAT Flight 367 1972 McDonnell Douglas DC-9-32 Terrorist bombingExplosive decompressionBomb explosion in cargo hold
American Airlines Flight 96 1972 Douglas DC-10-10 AccidentRapid decompression [43] Cargo door failure
Aeroflot Flight 109 1973 Tuploev Tu-104B Bombing81/81Explosive decompressionHijacker detonated explosive [44]
National Airlines Flight 27 1973 Douglas DC-10-10 AccidentExplosive decompression [45] Uncontained engine failure
Turkish Airlines Flight 981 1974 Douglas DC-10-10 AccidentExplosive decompression [46] Cargo door failure
USAF (registration unknown)1974 Boeing KC-135 Stratotanker Accident1/33Explosive decompressionSmall window broke at 35,000 feet [47]
TWA Flight 841 1974 Boeing 707-331BTerrorist bombingExplosive decompressionBomb explosion in cargo hold
1975 Tân Sơn Nhứt C-5 accident 1975 Lockheed C-5 Galaxy AccidentExplosive decompressionImproper maintenance of rear doors, cargo door failure
British Airways Flight 476 1976 Hawker Siddeley Trident 3B AccidentExplosive decompressionMid-air collision
Korean Air Lines Flight 902 1978 Boeing 707-320B ShootdownExplosive decompressionShootdown after straying into prohibited airspace over the Soviet Union
Air Canada Flight 6801979 McDonnell Douglas DC-9-32 Accident0/45Explosive decompressionFuselage tore open from fatigue [48]
Itavia Flight 870 1980 McDonnell Douglas DC-9-15 Bombing or Shootdown (Disputed)Explosive decompressionMid-air breakup due to explosion in the cabin (Cause of explosion disputed)
Saudia Flight 162 1980 Lockheed L-1011 TriStar AccidentExplosive decompressionTyre blowout
Far Eastern Air Transport Flight 103 1981 Boeing 737-222 AccidentExplosive decompressionSevere corrosion and metal fatigue
British Airways Flight 9 1982 Boeing 747-200 AccidentGradual decompressionEngine flameout due to volcanic ash ingestion
Reeve Aleutian Airways Flight 8 1983 Lockheed L-188 Electra AccidentRapid decompressionPropeller failure and collision with fuselage
Korean Air Lines Flight 007 1983 Boeing 747-200B ShootdownRapid decompression [49] [50] Intentionally fired air-to-air missile after aircraft strayed into prohibited airspace over the Soviet Union [51]
Gulf Air Flight 771 1983 Boeing 737-200 Terrorist bombingExplosive decompressionBomb explosion in cargo hold
Byford Dolphin accident 1983 Diving bell AccidentExplosive decompression Human error, no fail-safe in the design
Air India Flight 182 1985 Boeing 747-200B Terrorist bombingExplosive decompressionBomb explosion in cargo hold
Japan Airlines Flight 123 1985 Boeing 747SRAccidentExplosive decompressionDelayed structural failure of the rear pressure bulkhead following improper repairs
Space Shuttle Challenger disaster 1986 Space Shuttle Challenger AccidentGradual or rapid decompressionBreach in solid rocket booster O-ring, leading to damage from escaping superheated gas and eventual disintegration of launch vehicle
Pan Am Flight 125 1987 Boeing 747-121 IncidentRapid decompressionCargo door malfunction
LOT Polish Airlines Flight 5055 1987 Ilyushin Il-62MAccidentRapid decompressionUncontained engine failure
Aloha Airlines Flight 243 1988 Boeing 737-200 AccidentExplosive decompression [52] Metal fatigue
Iran Air Flight 655 1988 Airbus A300B2-203 ShootdownExplosive decompressionIntentionally fired surface-to-air missiles from the USS Vincennes
Pan Am Flight 103 1988 Boeing 747-100 Terrorist bombingExplosive decompressionBomb explosion in cargo hold
United Airlines Flight 811 1989 Boeing 747-122 AccidentExplosive decompressionCargo door failure
Partnair Flight 394 1989 Convair CV-580 AccidentExplosive decompressionRudder malfunction due to maintenance error, leading to loss of control and in-flight breakup
UTA Flight 772 1989 Douglas DC-10-30 Terrorist bombingExplosive decompressionBomb explosion in cargo hold
Avianca Flight 203 1989 Boeing 727-21Terrorist bombingExplosive decompressionBomb explosion igniting vapours in an empty fuel tank
British Airways Flight 5390 1990 BAC One-Eleven IncidentRapid decompression [53] Cockpit windscreen failure
Copa Airlines Flight 201 1992 Boeing 737-200 Advanced AccidentExplosive decompressionSpatial disorientation leading to steep dive and mid-air breakup
China Northwest Airlines Flight 2303 1994 Tupolev TU-154MAccidentExplosive decompressionImproper maintenance
Delta Air Lines Flight 1571995 Lockheed L-1011 TriStar AccidentRapid decompressionStructural failure of the bulkhead following inadequate inspection of the airframe [54]
TWA Flight 800 1996 Boeing 747-100 AccidentExplosive decompressionVapour explosion in fuel tank
Progress M-34 docking test 1997 Spektr space station moduleAccidentRapid decompressionCollision while in orbit
TAM Airlines Flight 2831997 Fokker 100 BombingExplosive decompressionBomb explosion [55]
SilkAir Flight 185 1997 Boeing 737-300 (Disputed)Explosive decompressionSteep dive and mid-air breakup (Cause of crash disputed)
Lionair Flight 602 1998 Antonov An-24RVShootdownRapid decompressionProbable MANPAD shootdown
1999 South Dakota Learjet crash 1999 Learjet 35 AccidentGradual or rapid decompression(Undetermined)
EgyptAir Flight 990 1999 Boeing 767-300ER (Disputed) [56] Explosive decompressionUncontrollable dive leading to mid-air breakup (Cause of crash disputed)
2000 Australia Beechcraft King Air crash 2000 Beechcraft Super King Air AccidentGradual decompressionInconclusive; likely pilot error or mechanical failure [57]
American Airlines Flight 12912000 Airbus A300-600RAccidentRapid decompressionCabin outflow valve malfunction. [58]
Hainan Island incident 2001 Lockheed EP-3 AccidentRapid decompressionMid-air collision
TAM Flight 9755 2001 Fokker 100 AccidentRapid decompressionUncontained engine failure [55]
China Airlines Flight 611 2002 Boeing 747-200B AccidentExplosive decompressionMetal fatigue
Space Shuttle Columbia disaster 2003 Space Shuttle Columbia AccidentExplosive decompression [59] Damage to orbiter thermal protection system at liftoff, leading to disintegration during reentry
Pinnacle Airlines Flight 3701 2004 Bombardier CRJ-200 AccidentGradual decompressionEngine flameout caused by pilot error
Helios Airways Flight 522 2005 Boeing 737-300 AccidentGradual decompressionPressurization system set to manual for the entire flight [60]
Alaska Airlines Flight 5362005 McDonnell Douglas MD-80 IncidentRapid decompressionFailure of operator to report collision involving a baggage loading cart at the departure gate [61]
Adam Air Flight 574 2007 Boeing 737-400 AccidentExplosive decompressionSpatial disorientation leading to steep dive and mid-air breakup
Qantas Flight 30 2008 Boeing 747-400 IncidentRapid decompression [62] Fuselage ruptured by oxygen cylinder explosion
Southwest Airlines Flight 2294 2009 Boeing 737-300 IncidentRapid decompressionMetal fatigue [63]
Southwest Airlines Flight 812 2011 Boeing 737-300 IncidentRapid decompressionMetal fatigue [64]
Asiana Airlines Flight 991 2011 Boeing 747-400F AccidentExplosive decompressionIn-flight fire leading to mid-air breakup. [65]
Malaysia Airlines Flight 17 2014 Boeing 777-200ER ShootdownExplosive decompressionShot down over Ukraine
Daallo Airlines Flight 159 2016 Airbus A321 Terrorist bombingExplosive decompressionBomb explosion in passenger cabin [66]
Southwest Airlines Flight 1380 2018 Boeing 737-700 AccidentRapid decompressionUncontained engine failure caused by metal fatigue [67] [68]
Sichuan Airlines Flight 8633 2018 Airbus A319-100 AccidentExplosive decompressionCockpit windscreen failure
2022 Baltic Sea Cessna Citation crash 2022 Cessna Citation II AccidentGradual decompressionUnder investigation
Alaska Airlines Flight 1282 2024 Boeing 737 MAX 9 Accident0/177Explosive decompressionDoor plug failure; under investigation. [69]

Myths

A bullet through a window may cause explosive decompression

In 2004, the TV show MythBusters examined whether explosive decompression occurs when a bullet is fired through the fuselage of an airplane informally by way of several tests using a decommissioned pressurised DC-9. A single shot through the side or the window did not have any effect – it took actual explosives to cause explosive decompression – suggesting that the fuselage is designed to prevent people from being blown out. [70] Professional pilot David Lombardo states that a bullet hole would have no perceived effect on cabin pressure as the hole would be smaller than the opening of the aircraft's outflow valve. [71]

NASA scientist Geoffrey A. Landis points out though that the impact depends on the size of the hole, which can be expanded by debris that is blown through it. Landis went on to say that "it would take about 100 seconds for pressure to equalise through a roughly 30.0 cm (11.8 in) hole in the fuselage of a Boeing 747." He then stated that anyone sitting next to the hole would have about half a ton of force pulling them towards it. [72] At least two confirmed cases have been documented of a person being blown through an airplane passenger window. The first occurred in 1973 when debris from an engine failure struck a window roughly midway in the fuselage. Despite efforts to pull the passenger back into the airplane, the occupant was forced entirely through the cabin window. [15] The passenger's skeletal remains were eventually found by a construction crew, and were positively identified two years later. [16] The second incident occurred on April 17, 2018, when a woman on Southwest Airlines Flight 1380 was partially blown through an airplane passenger window that had broken from a similar engine failure. Although the other passengers were able to pull her back inside, she later died from her injuries. [17] [18] [19] In both incidents, the plane landed safely with the sole fatality being the person seated next to the window involved. Fictional accounts of this include a scene in Goldfinger, when James Bond kills the eponymous villain by blowing him out a passenger window [73] and Die Another Day , when an errant gunshot shatters a window on a cargo plane and rapidly expands, causing multiple enemy officials, henchmen and the main villain to be sucked out to their deaths.

Exposure to a vacuum causes the body to explode

This persistent myth is based on a failure to distinguish between two types of decompression and their exaggerated portrayal in some fictional works. The first type of decompression deals with changing from normal atmospheric pressure (one atmosphere) to a vacuum (zero atmosphere) which is usually centered around space exploration. The second type of decompression changes from exceptionally high pressure (many atmospheres) to normal atmospheric pressure (one atmosphere) as may occur in deep-sea diving.

The first type is more common as pressure reduction from normal atmospheric pressure to a vacuum can be found in both space exploration and high-altitude aviation. Research and experience have shown that while exposure to a vacuum causes swelling, human skin is tough enough to withstand the drop of one atmosphere. [74] [75] The most serious risk from vacuum exposure is hypoxia, in which the body is starved of oxygen, leading to unconsciousness within a few seconds. [76] [77] Rapid uncontrolled decompression can be much more dangerous than vacuum exposure itself. Even if the victim does not hold their breath, venting through the windpipe may be too slow to prevent the fatal rupture of the delicate alveoli of the lungs. [78] Eardrums and sinuses may also be ruptured by rapid decompression, and soft tissues may be affected by bruises seeping blood. If the victim somehow survived, the stress and shock would accelerate oxygen consumption, leading to hypoxia at a rapid rate. [79] At the extremely low pressures encountered at altitudes above about 63,000 feet (19,000 m), the boiling point of water becomes less than normal body temperature. [74] This measure of altitude is known as the Armstrong limit, which is the practical limit to survivable altitude without pressurization. Fictional accounts of bodies exploding due to exposure from a vacuum include, among others, several incidents in the movie Outland , while in the movie Total Recall , characters appear to suffer effects of ebullism and blood boiling when exposed to the atmosphere of Mars.

The second type is rare since it involves a pressure drop over several atmospheres, which would require the person to have been placed in a pressure vessel. The only likely situation in which this might occur is during decompression after deep-sea diving. A pressure drop as small as 100 Torr (13 kPa), which produces no symptoms if it is gradual, may be fatal if it occurs suddenly. [78] One such incident occurred in 1983 in the North Sea, where violent explosive decompression from nine atmospheres to one caused four divers to die instantly from massive and lethal barotrauma. [80] Dramatized fictional accounts of this include a scene from the film Licence to Kill , when a character's head explodes after his hyperbaric chamber is rapidly depressurized, and another in the film DeepStar Six , wherein rapid depressurization causes a character to hemorrhage profusely before exploding in a similar fashion.

See also

Notes

  1. ↑ Notable exceptions include the Airbus A380, Boeing 787, and Concorde

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Southwest Airlines Flight 3472 was a regularly scheduled passenger flight operating from New Orleans International Airport in New Orleans, Louisiana to Orlando International Airport in Orlando, Florida. On August 27, 2016, the Boeing 737-7H4, with 99 passengers and five crew, 12 minutes after departure from New Orleans, was climbing through 31,000 feet and heading east over the Gulf of Mexico when the aircraft's number one CFM International CFM56-7 engine suffered an engine failure. A fan blade in the engine broke due to a fatigue crack. The separated portion of the blade rotated within the engine, moving forward, striking the engine inlet. Debris from the damaged engine inlet punctured the left side of the fuselage causing a loss of cabin pressure and damaged the wing and empennage. Oxygen masks were deployed to passengers while the crew initiated an emergency descent to 10,000 feet. The aircraft then diverted to Pensacola International Airport for a safe landing about 20 minutes later without further incident. While the aircraft sustained substantial damage, there were no injuries.

<span class="mw-page-title-main">Southwest Airlines Flight 1380</span> Aviation accident

Southwest Airlines Flight 1380 was a Boeing 737-700 that experienced a contained engine failure in the left CFM56-7B engine after departing from New York–LaGuardia Airport en route to Dallas Love Field on April 17, 2018. The engine cowl was broken in the failure and cowl fragments damaged the fuselage, shattering a cabin window and causing explosive depressurization of the aircraft. Other fragments caused damage to the wing. The crew carried out an emergency descent and diverted to Philadelphia International Airport. One passenger was partially ejected from the aircraft and sustained fatal injuries, while eight other passengers sustained minor injuries. The aircraft was substantially damaged.

<span class="mw-page-title-main">Alaska Airlines Flight 1282</span> 2024 aviation accident

Alaska Airlines Flight 1282 was a scheduled U.S. domestic flight operated by Alaska Airlines from Portland International Airport in Portland, Oregon, to Ontario International Airport in Ontario, California. Shortly after takeoff on January 5, 2024, a door plug on the Boeing 737 MAX 9 aircraft, which was not bolted in place due to a manufacturing error, blew out causing an uncontrolled decompression of the aircraft. The aircraft returned to Portland for an emergency landing. All 171 passengers and six crew members survived the accident, with three receiving minor injuries. An investigation of the accident by the National Transportation Safety Board (NTSB) is ongoing. A preliminary report published on February 6 said that four bolts, intended to secure the door plug, had been missing when the accident occurred and that Boeing records showed evidence that the plug had been reinstalled with no bolts prior to initial delivery of the aircraft.

References

  1. 1 2 3 4 "AC 61-107A – Operations of aircraft at altitudes above 25,000 feet msl and/or mach numbers (MMO) greater than .75" (PDF). Federal Aviation Administration. 2007-07-15. Retrieved 2008-07-29.
  2. 1 2 Dehart, R. L.; J. R. Davis (2002). Fundamentals Of Aerospace Medicine: Translating Research Into Clinical Applications, 3rd Rev Ed. United States: Lippincott Williams And Wilkins. p. 720. ISBN   978-0-7817-2898-0.
  3. ↑ Flight Standards Service, United States; Federal Aviation Agency, United States (1980). Flight Training Handbook. U.S. Dept. of Transportation, Federal Aviation Administration, Flight Standards Service. p. 250. Retrieved 2007-07-28.
  4. 1 2 "Chapter 7: Aircraft Systems". Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25B ed.). Federal Aviation Administration. 2016-08-24. p. 36. Archived from the original on 2023-06-20.
  5. ↑ Robert V. Brulle (2008-09-11). "Engineering the Space Age: A Rocket Scientist Remembers" (PDF). AU Press. Archived from the original (PDF) on 2011-09-28. Retrieved 2010-12-01.
  6. ↑ Kenneth Gabriel Williams (1959). The New Frontier: Man's Survival in the Sky. Thomas. Retrieved 2008-07-28.
  7. ↑ "AC 61-107A - Operations of aircraft at altitud above 25,000 feet MSL and/or mach numbers (MMO) greater than .75" (PDF). Federal Aviation Administration . July 15, 2007.
  8. 1 2 3 4 Martin B. Hocking; Diana Hocking (2005). Air Quality in Airplane Cabins and Similar Enclosed Spaces. Springer Science & Business. ISBN   3-540-25019-0 . Retrieved 2008-09-01.
  9. 1 2 Bason R, Yacavone DW (May 1992). "Loss of cabin pressurization in U.S. Naval aircraft: 1969–90". Aviat Space Environ Med. 63 (5): 341–345. PMID   1599378.
  10. ↑ Brooks CJ (March 1987). "Loss of cabin pressure in Canadian Forces transport aircraft, 1963–1984". Aviat Space Environ Med. 58 (3): 268–275. PMID   3579812.
  11. ↑ Mark Wolff (2006-01-06). "Cabin Decompression and Hypoxia". theairlinepilots.com. Retrieved 2008-09-01.
  12. ↑ Robinson, RR; Dervay, JP; Conkin, J. "An Evidenced-Based Approach for Estimating Decompression Sickness Risk in Aircraft Operations" (PDF). NASA STI Report Series. NASA/TM—1999–209374. Archived from the original (PDF) on 2008-10-30. Retrieved 2008-09-01.
  13. ↑ Powell, MR (2002). "Decompression limits in commercial aircraft cabins with forced descent". Undersea Hyperb. Med. Supplement (abstract). Archived from the original on 2011-08-11. Retrieved 2008-09-01.{{cite journal}}: CS1 maint: unfit URL (link)
  14. ↑ Daidzic, Nihad E.; Simones, Matthew P. (March–April 2010). "Aircraft Decompression with Installed Cockpit Security Door". Journal of Aircraft. 47 (2): 490–504. doi:10.2514/1.41953. [A]t 40,000 ft (12,200 m), the International Standard Atmosphere (ISA) pressure is only about 18.8 kPa (2.73 psi), and the air temperatures are about −56.5 °C (217 K). The boiling temperature of water at this atmospheric pressure is about−59 °C (332 K). Above 63,000 ft or 19,200 m (Armstrong line), the ISA environmental pressure drops below 6.3 kPa (0.91 psi) and the boiling temperature of water reaches the normal human body temperature (about 37 C). Any prolonged exposure to such an environment could lead to ebullism, anoxia, and ultimate death, after several minutes. These are indeed very hostile conditions for human life.
  15. 1 2 Mondout, Patrick. "Curious Crew Nearly Crashes DC-10". Archived from the original on 2011-04-08. Retrieved 2010-11-21.
  16. 1 2 Harden, Paul (2010-06-05). "Aircraft Down". El Defensor Chieftain. Archived from the original on 2019-10-17. Retrieved 2018-10-24.
  17. 1 2 Joyce, Kathleen (April 17, 2018). "Southwest Airlines plane's engine explodes; 1 passenger dead". Fox News .
  18. 1 2 Lattanzio, Vince; Lozano, Alicia Victoria; Nakano, Denise; McCrone • •, Brian X. (17 April 2018). "Woman Partially Sucked Out of Jet When Window Breaks Mid-Flight; Plane Makes Emergency Landing in Philadelphia".
  19. 1 2 Stack, Liam; Stevens, Matt (April 17, 2018). "A Southwest Airlines Engine Explodes, Killing a Passenger". The New York Times . Retrieved April 18, 2018.
  20. ↑ Lauren McMah (April 18, 2018). "How could a passenger get sucked out of a plane – and has it happened before?". www.news.com.au. Retrieved April 18, 2018.
  21. ↑ George Bibel (2007). Beyond the Black Box. JHU Press. pp. 141–142. ISBN   978-0-8018-8631-7 . Retrieved 2008-09-01.
  22. ↑ "FAA Historical Chronology, 1926–1996" (PDF). Federal Aviation Administration. 2005-02-18. Archived from the original (PDF) on 2008-06-24. Retrieved 2008-09-01.
  23. ↑ US 6273365
  24. ↑ "RGL Home Page". rgl.faa.gov.
  25. ↑ "Section 25.841: Airworthiness Standards: Transport Category Airplanes". Federal Aviation Administration. 1996-05-07. Retrieved 2008-10-02.
  26. 1 2 "Flightsim Aviation Zone - Number 1 Flight Simulation & Aviation Resource! - Flight Simulator, Aviation Databases". www.flightsimaviation.com.
  27. 1 2 "Exemption No. 8695". Renton, Washington: Federal Aviation Administration. 2006-03-24. Archived from the original on 2009-03-27. Retrieved 2008-10-02.
  28. ↑ Steve Happenny (2006-03-24). "PS-ANM-03-112-16". Federal Aviation Administration . Retrieved 2009-09-23.
  29. ↑ "Amendment 25–87". Federal Aviation Administration . Retrieved 2008-09-01.
  30. ↑ "Rapid Decompression In Air Transport Aircraft" (PDF). Aviation Medical Society of Australia and New Zealand. 2000-11-13. Archived from the original (PDF) on 2010-05-25. Retrieved 2008-09-01.
  31. ↑ "Woman sucked from Southwest Airlines plane died of 'blunt trauma'". Sky News.
  32. ↑ "ASN Aircraft accident Boeing 377 Stratocruiser 10-26 N1030V Rio de Janeiro, RJ" . Retrieved December 22, 2021.
  33. ↑ Neil Schlager (1994). When technology fails: Significant technological disasters, accidents, and failures of the twentieth century. Gale Research. ISBN   0-8103-8908-8 . Retrieved 2008-07-28.
  34. ↑ "ASN Aircraft accident Douglas DC-7 N316AA Memphis, TN". aviation-safety.net. Retrieved 2023-01-23.
  35. ↑ "(Untitled)" . Retrieved February 2, 2022.
  36. ↑ Ranter, Harro. "ASN Aircraft accident Avro 748-105 Srs. 1 LV-HHB Saladas, CR". aviation-safety.net. Retrieved 2022-02-17.
  37. ↑ "ASN Aircraft accident Vickers 701 Viscount G-AMON Barcelona". aviation-safety.net. Retrieved 2023-01-23.
  38. ↑ Shayler, David (2000). Disasters and Accidents in Manned Spaceflight. Springer. p. 38. ISBN   1852332255.
  39. ↑ "Two MSC Employees Commended For Rescue in Chamber Emergency" (PDF), Space News Roundup, Public Affairs Office of the National Aeronautics and Space Administration Manned Spacecraft Center, vol. 6, no. 6, p.  3, January 6, 1967, retrieved July 7, 2012, ...the suit technician who was inside the eight-foot [240 cm] altitude chamber, lost consciousness when his Apollo suit lost pressure when an oxygen line let go. The chamber was at approximately 150,000 [equivalent] feet [46,000 m] at the time of the accident...
  40. ↑ "ASN Aircraft accident Douglas DC-6B N8224H Holmdel, NJ". aviation-safety.net. Retrieved 2023-01-23.
  41. ↑ "ASN Aircraft accident Douglas C-133B Cargomaster 59-0530 Palisade, NE". aviation-safety.net. Retrieved 2023-01-23.
  42. ↑ Ivanovich, Grujica S. (2008). Salyut – The First Space Station: Triumph and Tragedy. Springer. pp. 305–306. ISBN   978-0387739731.
  43. ↑ "Aircraft accident report: American Airlines, Inc. McDonnell Douglas DC-10-10, N103AA. Near Windsor, Ontario, Canada. June 12, 1972" (PDF). National Transportation Safety Board. 1973-02-28. Retrieved 2009-03-22.
  44. ↑ "ASN Aircraft accident Tupolev Tu-104B CCCP-42379 Chita". aviation-safety.net. Retrieved 2023-01-23.
  45. ↑ "explosive decompression". Everything2.com. Retrieved 2017-08-08.
  46. ↑ "FAA historical chronology, 1926–1996" (PDF). Federal Aviation Administration. 2005-02-18. Archived from the original (PDF) on 2008-06-24. Retrieved 2008-07-29.
  47. ↑ "ASN Aircraft accident Boeing KC-135 Stratotanker registration unknown Fort Nelson, BC". aviation-safety.net. Retrieved 2023-01-23.
  48. ↑ "ASN Aircraft accident McDonnell Douglas DC-9-32 CF-TLU Boston, MA". aviation-safety.net. Retrieved 2023-01-23.
  49. ↑ Brnes Warnock McCormick; M. P. Papadakis; Joseph J. Asselta (2003). Aircraft Accident Reconstruction and Litigation. Lawyers & Judges Publishing Company. ISBN   1-930056-61-3 . Retrieved 2008-09-05.
  50. ↑ Alexander Dallin (1985). Black Box . University of California Press. ISBN   0-520-05515-2 . Retrieved 2008-09-06.
  51. ↑ United States Court of Appeals for the Second Circuit Nos. 907, 1057 August Term, 1994 (Argued: April 5, 1995 Decided: July 12, 1995, Docket Nos. 94–7208, 94–7218
  52. ↑ "Aging airplane safety". Federal Aviation Administration. 2002-12-02. Retrieved 2008-07-29.
  53. ↑ "Human factors in aircraft maintenance and inspection" (PDF). Civil Aviation Authority. 2005-12-01. Archived from the original (PDF) on 2008-10-30. Retrieved 2008-07-29.
  54. ↑ "Accident Description". Aviation Safety Network. 1995-08-23. Retrieved 2020-06-08.
  55. 1 2 "Fatal Events Since 1970 for Transportes Aéreos Regionais (TAM)". airsafe.com. Retrieved 2010-03-05.
  56. ↑ "Death and Denial". IMDb .
  57. ↑ Australian Transport Safety Bureau 2001, p. 26.
  58. ↑ Ranter, Harro. "Accident Airbus A300B4-605R N14056, 20 Nov 2000". www.aviation-safety.net. Aviation Safety Network . Retrieved 2021-11-17.
  59. ↑ "Columbia Crew Survival Investigation Report" (PDF). NASA.gov. 2008. pp. 2–90. The 51-L Challenger accident investigation showed that the Challenger CM remained intact and the crew was able to take some immediate actions after vehicle breakup, although the loads experienced were much higher as a result of the aerodynamic loads (estimated at 16 G to 21 G).5 The Challenger crew became incapacitated quickly and could not complete activation of all breathing air systems, leading to the conclusion that an incapacitating cabin depressurization occurred. By comparison, the Columbia crew experienced lower loads (~3.5 G) at the CE. The fact that none of the crew members lowered their visors strongly suggests that the crew was incapacitated after the CE by a rapid depressurization. Although no quantitative conclusion can be made regarding the cabin depressurization rate, it is probable that the cabin depressurization rate was high enough to incapacitate the crew in a matter of seconds. Conclusion L1-5. The depressurization incapacitated the crew members so rapidly that they were not able to lower their helmet visors.
  60. ↑ "Aircraft Accident Report – Helios Airways Flight HCY522 Boeing 737-31S at Grammatike, Hellas on 14 August 2005" (PDF). Hellenic Republic Ministry Of Transport & Communications: Air Accident Investigation & Aviation Safety Board. Nov 2006. Archived from the original (PDF) on 2011-06-05. Retrieved 2009-07-14.
  61. ↑ "Airline Accident: Accident – Dec. 26, 2005 – Seattle, Wash". Investigative Reporting Workshop. Archived from the original on 2018-01-20. Retrieved 2017-08-08.
  62. ↑ "Qantas Boeing 747-400 depressurisation and diversion to Manila on 25 July 2008" (Press release). Australian Transport Safety Bureau. 2008-07-28. Archived from the original on 2008-08-03. Retrieved 2008-07-28.
  63. ↑ "Hole in US plane forces landing". BBC News. 2009-07-14. Retrieved 2009-07-15.
  64. ↑ "Southwest Jet Had Pre-existing Fatigue". Fox News. 2011-04-03.
  65. ↑ Crash Into The Sea After An In-Flight Fire, Asiana Airlines, Boeing 747-400F, HL7604, International Waters 130 km West Of Jeju International Airport, 28 July 2011 (PDF) (Report). Aviation and Railway Accident Investigation Board. 24 July 2015. ARAIB/AAR1105. Retrieved 11 May 2019– via SKYbrary.
  66. ↑ "2016-02-02 Daallo Airlines A321 damaged by explosion at Mogadishu » JACDEC". www.jacdec.de (in German). Retrieved 2018-08-05.
  67. ↑ "Southwest Flight 1380 Statement #1 – Issued 11:00 a.m. CT". Southwest Airlines Newsroom. 17 April 2018.
  68. ↑ "Southwest flight suffers jet engine failure: Live updates". www.cnn.com. 17 April 2018.
  69. ↑ Gates, Dominic (January 5, 2024). "Alaska Airlines grounds MAX 9s after door plug blows out on Portland flight". The Seattle Times. Archived from the original on January 7, 2024. Retrieved January 6, 2024.
  70. ↑ Josh Sanburn (April 5, 2011). "Southwest's Scare: When a Plane Decompresses, What Happens?". Time. Retrieved April 18, 2018.
  71. ↑ Michael Daly and Lorna Thornber (April 18, 2018). "The deadly result when a large hole is ripped in the side of an aircraft". www.stuff.co.nz. Retrieved April 18, 2018.
  72. ↑ Lauren McMah (April 18, 2018). "How could a passenger get sucked out of a plane — and has it happened before?". www.news.com.au. Retrieved April 18, 2018.
  73. ↑ Ryan Dilley (May 20, 2003). "Guns, Goldfinger and sky marshals". BBC. It's not all fiction. If an airliner's window was shattered, the person sitting beside it would either go out the hole or plug it - which would not be comfortable.
  74. 1 2 Michael Barratt. "No. 2691 THE BODY AT VACUUM". www.uh.edu. Retrieved April 19, 2018.
  75. ↑ Karl Kruszelnicki (April 7, 2005). "Exploding Body in Vacuum". ABC News (Australia) . Retrieved April 19, 2018.
  76. ↑ "Advisory Circular 61-107" (PDF). FAA. pp. table 1.1.
  77. ↑ "2". Flight Surgeon's Guide. United States Air Force. Archived from the original on 2007-03-16.
  78. 1 2 Harding, Richard M. (1989). Survival in Space: Medical Problems of Manned Spaceflight. London: Routledge. ISBN   0-415-00253-2.
  79. ↑ Czarnik, Tamarack R. (1999). "Ebullism at 1 Million Feet: Surviving Rapid/Explosive Decompressionn" . Retrieved 2009-10-26.
  80. ↑ Limbrick, Jim (2001). North Sea Divers – a Requiem. Hertford: Authors OnLine. pp. 168–170. ISBN   0-7552-0036-5.
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