Talk:Cabin pressurization

Merge proposal

Where is the merge discussion? I have started it here because it links here but the merge proposer needs to explain the arguement for it first.

• Do not merge because: Unplanned cabin depressurisation is very specific to Cabin pressurization and is useful here. Uncontrolled decompression is a general case. Ex nihil (talk) 01:04, 7 August 2008 (UTC)

Changes:

• "Whenever a rapid decompression is faster than the inherent capability of the lungs to decompress"

This just doesn't happen on commercial jets, although maybe it's a problem for astronauts. When the pressure drops, you will exhale no matter how hard you try to keep it in. Sentence deleted.

• "When temperatures drop because of a decompression, injuries such as frostbite and hypothermia will begin to appear. "

If the reduced pressure after a decompression for hypothermia to set in, you're already dead. Sentence deleted.

• "Cabin pressurization has additional benefits - for instance, the air-tight environment partially protects passengers from the tremendous noise of the engines and cold temperatures in high altitudes."

Not really true: Pressurized aircraft are definitely not airtight, noise protection comes from the walls, and pressure does not protect from cold. Sentence deleted.

—Preceding unsigned comment added by 200.170.108.84 (talk) 22:10, 6 February 2008 (UTC)

I made some changes in the paragraph which mentions cabin altitude limits of 40,000 ft. and 25,000 ft. because I think the lay person might not understand that FAR was a reference solely to what limits had to apply in the event of a rapid decompression. Thus, I started the reference to that FAR (part 25, section 841) to show what the limit was during normal operations (8,000 ft.), and then went on to list the limits for cabin altitude in the event of a rapid decompression. I also changed the link because the one previously supplied was a very long document that dealt mostly with an application of the A-380 to have a special exemption. While that Word doc did contain the FAR part that we are concerned with here, one really has to wade thru a lot of other stuff to get that out of it. Thus, I linked to a sight that specializes in giving the wording of the particular FAR, without all the irrelevant stuff.

The previous link would still be a good one, if the subject matter is about the A-380 applying for an exemption, if that subject becomes a part of the article. Thanks. EditorASC (talk) 13:16, 20 September 2009 (UTC)

I have made further adjustments to the wording, so that it is clear the 1996 FAR amendment (25-87), applies only to newly designed aircraft. The older designs are "grandfathered" in and they are still legal to fly above FL 400, if they were so certified, prior to 1996. EditorASC (talk) 12:04, 25 September 2009 (UTC)

two deletions above

What is the problem that led to the deletion (described above) of hypothermia and frostbite? Those airliners do have drop-down oxygen masks. The pressure problem is hardly any more than Everest (29,000 feet), so as long as they are breathing O-2 they are likely victims for hypothermia and frstbite unless the airline falls to a lower altitude. On another point (also above), as any SCUBA diver knows, a decrease in ambient pressure does not force you to exhale -- if you hold your breath you can be a victime of alveolar rupture and air embolism. I think both of these delitions should be reversed. The other one is correct.

Mythbusters

Mythbusters tested this myth in their usual semi-scientific ways. Their findings are in no way proof.

"Semi-scientific" is too polite a term. "Mythbusters" uses methodologies and criteria for the public that are often outright contradictory to science (I can't watch it). Rapid decompression is a dependent on the size of the hole as well as the volume and pressure of the cabin - and the delta pressure (altitude). It can be calculated, but one can't make an absolute statement because pressure,cabin volumes, delta pressure (and window areas) are not uniform.

Speaking of myths, I have removed the following statements from the article, because they are false.

The aircraft's captain may elect to maintain cabin altitude at sea level on request to address compelling pressure-sensitive medical needs of a particular passenger, but at an operational cost to the airline arising from fuselage fatigue.

Nowadays, nearly all commercial airliners can maintain their cabin altitude at sea level throughout the flight if the captain sees a compelling reason to do so.

EditorASC (talk) 12:17, 28 August 2009 (UTC)

I have removed this statement:

Aircraft cabin air quality has become an occupational health and safety issue.Toxic planes: CASA questioned

For the following reasons:

a) The link is dead, thus no source to support that very controversial statement.

b) Assuming that some crewmember actually was made sick by cabin air that had been contaminated as a result of the failure of some petrol seal, that hardly turns the quality of cabin air into an occupational safety issue, in light of the fact that millions upon millions of passengers travel each year in airliners, without getting sick from airliner cabin air. The truth is that the alleged issue of polluted cabin air, was first made an issue by militant flight attendant unions during protracted contract negotiations. They began beating that drum, as part of their "industrial action" tactic, which was intended to put pressure on their airline employer to quickly settle the contract in their favor. After the contracts were signed, that "issue" quietly floated away. It is quite improper to use Wikipedia as a platform for disseminating union propaganda. EditorASC (talk) 04:23, 20 September 2009 (UTC)

Whilst the jury is out on the LONG TERM medical effects of contaminated cabin air, there is absolutely no doubt that vapour from the engine oil systems does contaminate the air in ALL cabins pressurised using engine bleed air, it is absolutely inescapable. The amount of contamination varyies according to the design of the engine and the efficiency of the seals. All gas turbine engines use differential air pressure across restricted leak path seals to contain the engine cooling air contaminated by oil vapour, when these seals lose their efficiency, more oil can contaminate the bleed air used for cabin pressurization. To say that there is no issue is a complete falsehood, the issue is HOW MUCH does contaminated air affect cabin staff (Passengers having relatively low exposure, so will show minimal effects). Forgot to signPetebutt (talk) 09:08, 16 March 2010 (UTC)

I decided to remove the following paragraph, along with its citation sources, for reasons to follow:

Bleed air extraction from the engines reduces engine efficiency only slightly but introduces a danger of oils and other chemicals from the engine being supplied to the cabin. The BAe 146 has achieved some notoriety with this problem, with some pilots refusing to fly it.Pilots refuse to fly BAe 146 in polluted cabin air row A vivid description of this happening appeared in a 2008 Telegraph article.Is cabin air making us sick?

Neither source meets Wiki RS requirements. The first link goes to a source that requires you to sign up and pay, to read the entire article. The "free" teaser first part of the article provides no information that would act as a reliable source for the claim in that paragraph.

The second source amounts to a scandal sheet article, which is based on nothing more that anecdotal allegations from some cabin and flight crews. "Unnamed sources" said, or such and such reported that they got sick. Absolutely no valid scientific studies cited, in that rag article, which can verify that

a) bleed air pressurization design is responsible for making passengers and/or crew sick, or that

b) bleed air pressurization design makes the risk of cabin air being contaminated, any higher than other or previous design methods.

I have researched this subject for many years and have read many studies from reputable sources, and none of them ever found that airliner cabin air was less than adequate for crew and passengers combined. In most cases, the cabin air in the typical airliner is fresher and totally exhausted and replaced, much faster than in the average office building. They did find that humidity tends to be low (3 to 5 % is typical), but also that CO2 has always been at less than regulatory limit levels, and that so-called "toxic" contamination from hydrualic fluid or engine oil is extremely rare, and even when that has happened, no evidence that it constituted a significant health threat. Further, that the percentage of available oxygen in the cabin atmosphere remains pretty much the same as at sea level. The modern ECS contain filters that effectively deal both with viruses and excessive ozone.

The truth is that flight attendant labor unions have used this myth allegation for years against the managements of their own airlines, as an "Industrial Action" tool, which is designed to put pressure on management, to settle union demands during contract negotiations. That is what these kinds of allegations have been, and are still about. Boeing ECS equipment and design has always met the standards of NASA, the FAA amd ICAO, among others, and there isn't one shred of valid scientific evidence that airliner cabin air is a threat to the health of anyone on board----unless, of course, a raging fire starts in the cabin, before landing.... EditorASC (talk) 03:33, 26 January 2010 (UTC)

Where is your evidence. I am an aircraft engineer and I KNOW that engine oil DOES contaminate cabin air in ALL aircraft pressurized by engine bleed air. The issue is how much and what is a safe level for the exposure that cabin crew will typically experience.forgot to sign here tooPetebutt (talk) 09:09, 16 March 2010 (UTC)

The issue is discussed in detail at [[1]], in the article itself and in the talk page. You are correct, that the issue is how often seals leak, and how much they leak---when leaks actually occur----and then how much of toxic substances are ingested by SOBs, in terms of PPMs. The burden of proof, as to how often, how much, and if it ever rises to the level of injury to anyone, lies with those making the claims. So far, no one has ever been able to provide scientific evidence to support the claims. To the contrary, it is more likely that the very rare times when some experience symptoms of irritation, it is the result of something like the excessive use of formaldehyde in the toilets and for cleaning galleys, etc., as well as other possible sources of irritation, such as de-icing fluid, hydraulic fluid, or even in substances in baggage which passengers bring along with them. The two organizations which are trying to gain acceptance of this mythical "disease," are those which are populated by those who want to get huge awards for their members, via the Workman's Compensation Insurance laws. EditorASC (talk) 10:03, 16 March 2010 (UTC)

First aircraft

Some people think that the Lockheed XC-35 was the first, and not the Boeing 307; However the first did not enter production.

[2] Dagoflores --189.166.14.226 (talk) 08:20, 12 January 2008 (UTC)

That does not mean that the XC-35 was not the first pressurized aircraft. That would be like saying that the Bell X-1 was not the first supersonic aircraft because it did not go into production. Ratsbew (talk) 20:17, 20 November 2008 (UTC)

There seems to be disagreement between this article (stating that the XC-35 was the first pressurised aircraft) and that on the Junkers 49, which explicitly states it was the first, flying before the XC-35. Can someone who knows their stuff correct one or the other? —Preceding unsigned comment added by 78.86.228.109 (talk) 21:52, 21 January 2009 (UTC)

Well, the Ju49 was making high altitude flights by 1935, and the XC-35 did not fly until 9 May 1937, you work it oput!Petebutt (talk) 09:14, 16 March 2010 (UTC)

Difference between cabin and cargo

Does anyone know what the difference between the pressure in the cabin relative to the cargo area is? How much pressure is your luggage subjected to (if the pressure in the cabin is 0.7 bar? When does spray bottles break?

Thanks —The preceding unsigned comment was added by 63.240.133.93 (talk) 02:07, 16 March 2007 (UTC).

My uncle (a retired airline pilot) said that the cargo area is pressurized exactly the same as the cabin since they often carry pets down there. In newer planes it is even heated and uses the same ventilation system as the regular cabin.-- Nick. 08:49, 21 September 2007 EST. —Preceding unsigned comment added by 65.112.23.131 (talk)

Most cabin cargo bins are pressurized, although there are exceptions. As for heating, some bins have their own heaters, and some receive residual heat from the passenger cabins. In the second case (residual heat), the bins can get chilly. Mikepurves (talk) 09:06, 26 July 2008 (UTC)

Pressure and speed of escape at a pinhole

"An otherwise-harmless pinhole under these pressure differences will generate a high-pitched squeal as the air leaks out at supersonic speeds[citation needed]." --This does not seem right, because even assuming a complete vaccum (due to aerodynamic effects, if any) just outside the skin of the aircraft, the pressure differential is less than 10 PSI, and a pinhole in a car tire (30 psi) does not generate such a loud noise. —Preceding unsigned comment added by 200.170.108.84 (talk) 21:42, 6 February 2008 (UTC)

I join in the comment. The claim of air escaping at "supersonic speeds" seems implausible on its face. Sound is caused by the movement of molecules. The speed of sound is the upper limit. It appears that by definition, the upper speed limit of fluid escaping a pressure vessel would be the speed of sound, and that escaping air is not likely to hit that upper limit for the reasons stated above.

The only way to move a fluid above the speed of sound is to have a solid object strike it, physically pushing it out of the way.

I am not a physicist, but this appears to be basic fluid dynamics.

Mikepurves (talk) 08:56, 26 July 2008 (UTC)

This may have been sorted out in the article, but sonic flow through an orifice is a common occurrence. Supersonic flow is less likely and depends on specific geometry of the flow passage. See Choked flow. Cheers, • • • Peter (Southwood) ^(talk): 09:49, 21 July 2013 (UTC)

"A 5' hole will decompress an airliner in a fraction of a second"

I don't have the data, but this blanket assertion is highly dubious. There are many variables which go into the rate of decompression.

First, all airliners are continously pumping in fresh air, and dumping pressurized air overboard. On virtually all jet transports, the engines pump pressurized air into the plane (the 787 will have a separate compressor system). "Outflow valves" leak the cabin air overboard, and the pressurization controller controls the rate in which the outflow valves leak the air overboard. All airliners have unintended leaks (some more, some less), and the pressurization controller closes the outflow valves more to compensate.

If the airplane suffers a large-enough hole, the outflow valves will close altogether while fresh air continues to be pumped into the plane. If the hole is too large, the airplane will begin to lose pressure (failure of all engines would have a similar effect as all incoming air would be shut off). Legend says (I cannot confirm this) that the Boeing 777 can maintain pressure with three windows out.

The total pressure vessel volume, the inside/outside pressure differential, the rate of air inflow and the rate of air outflow will determine how quickly an airplane will depressurize. A blanket statement that a 5' diameter hole causes instant decompression is far too oversimplified and almost certainly at odds with the facts. It fails to take into account different airplanes' cabin volumes (an Airbus 380 or a Boeing 747 has a bit more volume than, say a DC-9 or F-28), different engine, and the different cabin inflow and outflow configurations.

Finally, remember that a cabin which is not maintaining pressure ("leaking up") is not the same thing as an instant equalization with the ambient (outside) air pressure. To instantly equalize the pressure of a large volume of cabin air with the outside, the hole has to be massive, e.g., the airplane blown in half. A slower decompression allows plenty of time to address the problem while oxygen masks are deployed and a descent is started.

Mikepurves (talk) 06:13, 26 July 2008 (UTC)

Minor edit 7/31/08 Mikepurves (talk) 19:17, 31 July 2008 (UTC)

Intentional tweaking of the cabin altitude

I've heard several reports, none independently verifiable as yet, that airlines routinely increase the cabin altitude during longhaul flights (e.g. after meals) in order to save fuel and to the settle the passengers down quicker by decreasing the amount of oxygen in the cabin (within allowable tolerances). Has anyone else come across this before? If so, do you have a reference please? Socrates2008 (Talk) 15:02, 5 September 2008 (UTC)

---

I am a former airline pilot for a US domestic airline. I have serious doubts that any US-based airline would do this, for the following reasons:

1. Pursuant to Federal Aviation Regulations, the airplane's cabin altitude must be kept below 8,000 feet. Because each flight's pressurization and depressurization puts stress on the pressure vessel (remember the Aloha airlines burst fuselage), and the greater the inside/outside pressure differential, the greater the stress, most airliners flying at their service ceilings will not be capable of a cabin altitude much lower than 8,000 feet. In other words, if the airplane is flying at its ceiling, the pilots don't have the discretion to raise the cabin, and the airplane doesn't have the physical capability of lowering it.

2. There are already health considerations associated with the reduced cabin pressure at altitude. Elderly people with pulmonary problems or circulation problems can develop health issues even under the normally lower air pressure at altitude, and flight diversions for these are more common than you might expect. Pregnant women may have problems with their fetuses. Any scuba divers on board are at an elevated risk of decompression sickness. People who have consumed too much alcohol have the effects magnified, and are more likely to cause the cabin crew or other passengers trouble. On any given flight, the pilots don't know whether anyone, or who, could be affected by one or more of these. Deliberately raising the cabin increases the risks to all of them. Doing so as an act of discretion would expose the pilots and the airline to lawsuits.

My guess is that it is an urban legend. It is extremely unlikely that any airline would authorize the practice. It is possible that some pilots, somewhere, have done this. If they had, it would have constituted extremely poor judgment on the pilots' part.

Mikepurves (talk) 17:23, 6 September 2008 (UTC)

As for "saving fuel" by reducing the volume of air in the cabin, I am unsure how that would work. The bleed air tapped off the engines to pressurize and heat or cool the cabin is a continuous process. Outflow valves at the back of the plane dump the air off, and the outflow valves (not the bleed air) directly regulate the pressure. The air is coming in anyway.

The only potential fuel savings would be by reducing the weight of the air in the cabin. How much weight difference there is between, say an 8,000' cabin and a 10,000' cabin I don't know (it would vary from plane to plane). I do know that the airlines are considering every available option to save fuel, and the idea might even have been batted around in an airline office somewhere. But since you would be breaking regulations and exposing your passengers and cabin crew to potential health problems, I just don't see it happening.

Airline managements and employees really do put their passengers' safety first: aviation gets dangerous very quickly if you do not.

The FAA's oversight of airlines is extremely close; every airline manager, every mechanic and every pilot and flight attendant gets to know the local "Feds" over time: they are regularly be observed in the process of doing their jobs. Flight records are pored over, and computer systems such as ACARS record flight parameters which are reviewed on a spot-check basis, and occasionally as part of a comprehensive investigation. When pilots fly their airplanes, two questions are continually running through their minds: Is what I am doing safe? And how do I explain it to management and to the FAA if they ask later -- am I adhering to company standards and FAA regulations, and showing the good judgment they expect of someone carrying 200 passengers with a $100 million piece of equipment? That internal dialog puts a stop to 98% of the "cowboy" actions that people might otherwise consider.

Finally, airlines are extremely sensitive to the public trust in their safety -- fear of news stories saying "airline risks passengers' health to save money" is a powerful motivator in this business. Because of aviation's high profile and a natural public fear of being high in the air but not in control, airlines know that aviation makes good press copy and raises circulation -- the press will report FAST on aviation matters, and the airlines don't want that kind of press. Every airline manager considers this all the time, and many employees do, too.

Mikepurves (talk) 17:50, 6 September 2008 (UTC)

I'm not suggesting that all airlines do this, or that they take the cabin pressure outside permissable legal limits. However I have a parachutist friend who recently flew on an unnamed national airline, and happened to have his altimeter on him, which indicated a clearly measurable drop in cabin pressure after dinner time until just before breakfast time. Co-incidence perhaps? Personally, I'm skeptical, but can appreciate that no airline would publish this information either. In any event, it's rumour unless we find a reference from a reputable source. Socrates2008 (Talk) 00:11, 7 September 2008 (UTC)

The only explanation, assuming his altimeter was accurate, is that the plane was on a "step-climb-cruise" flight plan, which is the norm for longer range flights. A typical 747-400 flight from LAX to SYD, will start out with an initial cruise altitude of FL 290, simply because the plane is too heavy to go higher. Later, after some fuel has been burned off, it will climb to the next higher flight level that is available. By the time it gets closer to SYD, it could be as high as FL 350 or 370. As the plane climbs above approximately 25,000 ft., the cabin altitude will climb too, to keep the differential pressure within limits.

When it gets close to the destination, it may have to descend to a lower altitude sooner than desired, if there are traffic conflicts. That could explain the cabin altitude coming back down somewhat, before the time of continual descent to the approach landing phase.

I have to agree with the retired airline captain above (I am one of those guys too). The pressurization is automatically controlled and the cabin altitude will not go higher than the programed limits (about 8,000 ft.), unless there is some sort of malfunction. While there is a manual control mode, it is only for emergency backup purposes, in case both the auto controllers fail (I never saw that happen, in 33 years of airline flying). It would be extremely difficult for the pilot to manually control the pressurization, without getting ear-splitting pressure surges. No pilot in his right mind would try that, unless he was forced to as a result of an auto control failure.

Since we are on that subject, I will remove the statement in the article that says the captain can elect to keep the cabin pressure at sea level, for special medical needs passengers. That may be possible for small air-ambulance flights, but total hogwash for airliners of any size. The only way to do that is to go to manual mode, AND fly at an altitude below 25,000 ft. On flights of more than a half-hour, that would require a much greater fuel load, and on long-range flights, the result would be that enroute fuel stops would have to be made. No pilot can force the plane to exceed the designed pressure limits. The double set of pressure relief valves would open. They are part of the design because overpressure, above design and legal operating limits, would be very dangerous. EditorASC (talk) 11:50, 28 August 2009 (UTC)

I have no doubt that there is considerable urban folklore and public misunderstanding involved here. As above, there is no need to mention any of this as there are no reliable refs right now. Socrates2008 (Talk) 13:11, 10 September 2009 (UTC)

Oh, I agree with that. I simply was explaining that what your parachutist friend observed, is a completely normal situation, since long-haul flights step-climb their FL altitudes and that does result in the cabin altitude step-climbing too. The plane has to automatically raise the cabin altitude, as the flight climbs to higher FLs, to prevent the pressure hull limits from being exceeded. EditorASC (talk) 09:34, 11 September 2009 (UTC)

Rubbish. The cabin altitude will go to the rated value (typically 8,000ft), as the aircraft climbs, and stay there. Step climbs and any other nonsense will not affect it unless the pressure controllers are malfunctioning!!!!!!!!!!!!Petebutt (talk) 09:50, 16 March 2010 (UTC)

Unfortunately, you don't seem to know what you are talking about. I have specific Captain's type ratings for the B-727, 757, 767, 777, 747-100-300, and the 747-400. I also was a cockpit crew member on the DC-6, B-720, DC-8 and the DC-10. The auto pressure controllers are programmed to keep the cabin altitude as low as possible, consistent with not exceeding the max allowed pressure differential for outside-to-inside, of approximately 8.6 PSI (various aircraft can vary a little, from that number, up or down).

Thus, the cabin altitude of a B-767 will be at less than 3,000 ft., if the plane is flying at FL 250. If the plane then climbs to FL 300, the cabin altitude will climb too, to just below 4,000 ft. If the plane then climbs to FL 390, the cabin altitude will climb to just under 7,000 ft. See the chart on page 6 of this Boeing document: [3] EditorASC (talk) 11:58, 16 March 2010 (UTC)

Rating re-assessment

I believe that this article has improved very considerably since rated start class and I have listed it for re-assessment at Wikipedia:WikiProject Aviation/Assessment. Ex nihil (talk) 00:27, 2 October 2008 (UTC)

Have Assessed as 'B'. As for improvement, it wouldn't hurt to add another image however, and a few more citations in the lead. \ / (⁂) 11:56, 10 October 2008 (UTC)

Units

Can I suggest using only fractions of atmospheres for the pressure units in this article? Bar/KPa are essentially this already but is there any reason that someone would need to know that the pressure is 12 psi? Wouldn't they then compare that to atmospheric pressure of 14.5psi? —Preceding unsigned comment added by Shniken (talk • contribs) 05:44, 4 June 2009 (UTC)

Carbon Dioxide: a small point of physiology

Re: "The low local partial pressure of carbon dioxide (CO2) causes CO2 to out-gas from the blood raising the blood pH and inducing alkalosis." The partial pressure of carbon dioxide at sea level is approximately 0.2 mm Hg (pressure at sea level = 760 mm Hg x percentage CO2 = 0.03%). The partial pressure of carbon dioxide in the alveoli of the lungs (and in arterial blood) is 40 mm Hg. Thus even at sea level the CO2 in the body is at almost 200 times that in the ambient atmosphere. The fall in carbon dioxide is mainly due to hyperventilation (increased rate and depth of breathing), caused by the low oxygen concentration at altitude. At very high altitudes it is irrelevant, as you will lose consciousness in seconds due hypoxia. —Preceding unsigned comment added by Mjwciw (talk • contribs) 10:04, 18 July 2009 (UTC)

Nonsense statement

"Pressurization is essential over 3,000 metres (9,800 ft) to prevent crew and passengers from becoming unconscious through the lack of oxygen (hypoxia) in the thin air above that altitude." This statement as it stands is nonsense. People do not become unconscious at 3000 meters. How do you think people live in Bolivia ? Eregli bob (talk) 12:08, 28 August 2009 (UTC)

Supplemental oxygen isn't required for crew or passengers unless above 15,000ft(cabin altitude). Obviously, there is a safety margin involved there. Most people will not actually lose consciousness until above 20,000ft(cabin altitude). — Preceding unsigned comment added by 65.36.69.148 (talk) 20:16, 14 November 2016 (UTC)

Sorry, but that is not accurate. Flight crew are required to use supplemental oxygen for cabin altitudes of 12,500 to 14,000 ft. when the duration is more than 30 minutes. And to use it for the entire time, if the altitude is 14,000 or higher. FAR 91.211. EditorASC (talk) 08:52, 21 December 2016 (UTC)

Pressurized flight

I have removed note # one, which read thus:

::"1. ^ Notable exceptions include the Airbus A380, Boeing 787 and Concorde"

For these reasons:

• The Concorde is not a notable exception any more than the other 8,000 aircraft, which were certified prior to the new (1996, FAR 25-87) certification rules. Exceptions to that new rule, are only among the "newly designed" aircraft. Concorde was one of the older aircraft designs, that were certified long before the new revision.

• The subsequent paragraph in the article, explains the successful exemption of the A380 (Either A380, or Airbus 380, but not both ways at the same time), complete with the appropriate citation, so there is no necessity to add an un-citated note to the previous paragraph. If the B787 has also been exempted, then the appropriate way to include that information, is to put it in the same paragraph with the A380 exemption and then to attach the proper citation, which also verifies that statement.

Here is how the subsequent paragraph currently reads:

However, companies that build the newer designed aircraft can apply for exemption from that more restrictive rule. In 2004, Airbus successfully petitioned the FAA to allow cabin pressure of the A380 to reach 43,000 feet in the event of a decompression incident, and to exceed 40,000 feet 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.[8]

Further exemptions of the "newly designed" planes should be added to that paragraph, with their verifying citations. EditorASC (talk) 01:38, 6 October 2009 (UTC)

small cabin windows

Concorde had to deal with unusually high pressure differentials, as of necessity it flew at unusually high altitude (up to 60,000 ft) while the cabin altitude was maintained at 6000 ft."Human Factors in the Concord". This made the vehicle significantly heavier and contributed to the high cost of a flight. Concorde also had to have smaller than normal cabin windows to limit decompression speed in the event of window failure.

I will search for evidence, but I think you will find that the small windows on Concorde and Tu-144 are dure to the need to keep cosmic radiation inflow to a minimum. Shoot me down if I'm wrong!Petebutt (talk) 08:48, 16 March 2010 (UTC)

If a window should fail, how rapidly the cabin altitude climbs, would be a function of the size of that lost window. The larger it was, the more rapidly the cabin altitude would climb and that would increase the danger of injury or death to passengers. I don't have the specs available, but my guess is that the loss of just one of those smaller windows, would result in a rather slow climbing of the cabin altitude, since the outflow valves would slam shut and the cabin air escaping thru that smaller window, wouldn't be too much more than the amount that the exhaust valves permitted, while keeping the cabin below the maximum limit altitude, under normal conditions. Thus, it makes sense that using smaller windows did provide a greater safety margin, in the event of the failure of one window. The subsequent emergency descent would take longer to reach a "safe" altitude, simply because the plane was flying at least 20,000 ft higher than other types of airliners. Using smaller windows is a logical way to offset the additional time it would take to make a rapid descent to a lower, safe, altitude, if a window did fail. EditorASC (talk) 09:36, 16 March 2010 (UTC)

" ... the need to keep cosmic radiation inflow to a minimum. Shoot me down if I'm wrong!" - sorry, you are wrong. As EditorASC writes, Concorde's windows were the size they were to limit the amount of cabin air escaping should a window break at 60,000 feet. In this case the aircraft would immediately slow down to below Mach 1 and begin an immediate descent, which would be very rapid as the aircraft was certified to use reverse thrust on two inner engines in flight, thus allowing a rate-of-descent of something like ten thousand feet per-minute. IIRC, after the initial Concorde design was completed the cabin pressurisation system was subsequently uprated in capacity to allow for the loss of a single window so enabling less rapid descents should a window fail. IIARC, the cabin windows themselves were triple-glazed, both for strength and for heat insulation, due to the outside skin temperature which was around 90C at Mach 2.— Preceding unsigned comment added by 95.149.173.74 (talk) 16:03, 16 May 2016 (UTC)

The pressure maintained within the cabin is referred to as the equivalent effective cabin altitude or more normally, the ‘cabin altitude’. Cabin altitude is not normally maintained at average mean sea level (MSL) pressure (1013.25 mbar, or 29.921 inches of mercury) throughout the flight, because doing so would cause the designed differential pressure limits of the fuselage to be exceeded. An aircraft planning to cruise at 40,000 ft (12,000 m) is programmed to rise gradually from take-off to around 8,000 ft (2,400 m) in cabin pressure altitude, and to then reduce gently to match the ambient air pressure of the destination. That destination may be significantly above sea level and this needs to be taken into account; for example, El Alto International Airport in La Paz, Bolivia is 4,061 metres (13,323 feet) above sea level.

This doesn't sound right. How does the controller know what the pressure is at La Paz or any other airport? Sounds like BS to me. If the altitude of an airport is above the rated altitude then the pressure controllers will try to maintain a pressure differential until the air supply is exhausted, i.e. engines shut down, when the pressure would gradually equalise. No need for BS.Petebutt (talk) 10:24, 16 March 2010 (UTC)

Perhaps if you read the Altimeter and Atmospheric pressure articles, you'd understand the relationship between air pressure and altitude (and hence how the former is derived from the latter, e.g. at El Alto International Airport) Socrates2008 (Talk) 12:16, 16 March 2010 (UTC)

New FAA Rules (FL400 max becomes FL450?)

After doing a Google search for the FARs that limit operating altitude to FL400, this immediately came up: http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgPolicy.nsf/0/90AA20C2F35901D98625713F0056B1B8?OpenDocument

It outlines that they have a new interim policy that allows a service ceiling of FL450. This is a 2006 document, and this page hasn't been updated with this information yet. I would do it if I were more familiar with the FAR approval process, but if this is currently in effect the information on this wiki page would be outdated. Could someone who knows who the FAA works please check this? 94.210.18.219 (talk) 10:28, 20 September 2010 (UTC)

Talk Page Rules

I just had to revert a recent edit, because one editor inserted his comments in the middle of a paragraph that was written by another editor. That is improper---comments by one editor should not be altered or broken up by another editor. If one wants to comment on what another editor said, then copy it and show it as a quotation, to which you are responding. It is NEVER proper to break up or alter what another editor said, on a Wiki TALK PAGE! Only Administrators have the right to delete comments on Talk Pages, and then only for some violation of Talk Page posting rules.

Additionally, when quoting and then responding to what another editor said, it should be posted in the same section where the original quotation was posted. It makes for serious confusion to the rest of us, if you post a response in one section, to statements made by another editor, in an entirely different section.

Finally, any post should not cause the page to go way wide, i.e., your post should not force others to have to slide the page back and forth on the horizontal scale, to read it. If you see that your post did that to the page, then you should correct it yourself right away. Please do not leave messes for others to clean up. Thanks for your consideration. EditorASC (talk) 11:11, 16 March 2010 (UTC)

Loss of pressurization section

Bilcat removed the Notable incident tables! Having recovered from the shock of that and accepting it reluctantly as the right decision, most of the rest of this section also needs to go for the same reason, it is redundant, being dealt with in Uncontrolled decompression and prone to contradiction. Ex nihil ^(talk) 01:13, 21 April 2010 (UTC)

BarotraUma

The "need for cabin pressurization" section doesn't make sense when it describes barotrama, because that section says that avoiding barotrama is one of the reasons that pressurizing flights is necessary, yet when it describes barotrama it only describes the symptoms of barotrama that people experience on pressurized flights. In contrast, the other three "illnesses" mentioned in that section appear to be described in terms of the symptoms that would be experienced on unpressurized flights above 3000 meters, which makes more sense in context.

While I think this information is important to present in some way and perhaps even expand on (i.e. many people experience ear pain from mild barotrama due to normal, controlled cabin pressure changes) the way it's presented in this section is strange.

69.181.161.106 (talk) 04:02, 6 January 2011 (UTC)

Interesting point: In naval aircraft and probably other types, insufficient cabin altitude can also cause tooth pain due to tiny pockets of air trapped in poorly done dental repairs.166.147.104.25 (talk) 21:14, 19 September 2013 (UTC)

Another confused sentence in lede

At the beginning of the article is a sentence:

A typical cabin altitude is the Boeing 767's maintained at an altitude of 2,100 metres (6,900 ft) when cruising at 12,000 metres (39,000 ft),[1] The trend is to lower the cabin altitude in new aircraft, the lowest currently flying is the Airbus A380 at 1,520 m (5,000 ft).[2][3]

First, "cabin altitude" is used without any additional explanation, even if it is used as a pressure unit all over the article. Second, it used a capital "t" after a comma. Third, it tries to say too much in a single sentence. I begun to understand it only after the third reading. It needs a strong cleanup. --Xerces8 (talk) 20:43, 21 August 2011 (UTC)

I changed it.--Patrick (talk) 22:19, 21 August 2011 (UTC)

Contrary to the statement above, the Airbus 380 is now an example in the article for a plane with a relatively low pressured cabine (comparing to Boeing 767). According to what I found, this may some kind of misleading: "The A380 produces 50% less cabin noise than a 747 and has higher cabin air pressure (equivalent to an altitude of 1500 metres (5000 ft) versus 2500 metres (8000 ft))"

Source: http://www.globalaircraft.org/planes/airbus_a380.pl 78.34.57.185 (talk) 13:31, 15 March 2014 (UTC)

Wiki conventions for naming crew members in airliner accident articles

I am wondering if Wikipedia has any rules or guidelines about when and how to name the crew members on accident flights? I have recently noticed that in some articles, no crew member names are given at all [here], and in other accidents, the full crew (both cockpit & cabin) are named [here], and in still others only the Captains and First Officers are named [here]. Is that disparity just the result of happenstance, as to who first writes an article, or is it by design? It would be helpful for some of us IP editors if someone can explain if there are some specific guidelines to follow, on this aspect of aviation accident articles. Thank you, 66.81.52.230 (talk) 11:02, 23 October 2011 (UTC)

More happenstance, depending on who wrote it and whether the source for the incident gave names. GraemeLeggett (talk) 13:46, 23 October 2011 (UTC)

Thank you for that prompt response. I surmise then that no one would object if I add crew members names in those articles that don't have them, if they where listed in the official accident reports. 66.81.52.253 (talk) 22:24, 23 October 2011 (UTC)

Pressurization of cargo space and doors.

I'm assuming that both the passenger cabin and the freight space on an airliner are pressurized. If so, there is an anomaly. Passenger doors open inwards to help ensure cabin pressure keeps the doors closed, but the undercarriage doors (undercarriage is often partly or completely retracted within the fuserlarge, esp nose wheel) open outwards creating a greater risk. It would also require the cabin to be depressurised before lowering undercarriage (not unreasonable). Is this right, or is the freight space not pressurised (the cabin floor looks to me to be stronger than the cabin wall)? Presumably one of you experts know the answer and can add it to the article for completeness.FreeFlow99 (talk) 19:03, 15 November 2012 (UTC)

• The undercarriage storage wells are isolated from the cargo space and are not pressurised. The undercarriage doors are merely aerodynamic fairings and are not even a tight fit. Ex nihil ^(talk) 06:00, 16 November 2012 (UTC)

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Boeing 747 vs. Airbus A380 comparison

I changed a sentence under "Aircraft" to correctly reflect the content in the reference that was cited for it. The reference clearly says that the Boeing 747 carries a relatively high cabin pressure (CP), or equivalently a relatively low equivalent cabin pressure altitude, than the Airbus A380. The sentence said the reverse, and included a cabin altitude figure for the Boeing 747 that was simply fictitious, not based on any source at all.

This edit was reverted by Ex nihil with the explanation "Change, and the article, refers to operational decisions by airlines and not to the design CP by manufacturers" but this doesn't make any sense. If the "design CP" for the 747 was as low as was implied by the original statement that I changed, it would not be possible for airline "operational decisions" to produce the higher pressure / lower pressure altitude described in the reference.

Looking around online for more information on this topic, I found [4]. I can't really say that this website is a reliable source, but it does show that the 747 has a higher maximum pressure differential than the A380 (8.9 psi vs 8.6 psi), which is consistent with the facts as described in the existing reference.

So I think my original edit here is solid and should not be reverted again without citing a source of information that contradicts it. 71.197.166.72 (talk) 01:57, 12 December 2015 (UTC)

I agree that Ex nihil was out of order when he reverted your edit and restored statements that were not compatible with the cited source. If he was determined to revert your edit he should have removed the in-line citation and replaced it with a “Citation needed” tag.

The whole subsection titled “Aircraft” is poorly presented. In places it looks more like a student essay than something in an encyclopaedia. Wikipedia does not see its role as publishing comparisons between competing products and yet, in places within “Aircraft”, there are some unencyclopaedic comparisons. I have already removed one unsourced statement of doubtful meaning - diff. If you are inclined to help clean-up the “Aircraft” section please feel welcome to do so!

Referring to the 2010 article published by the European Respiratory Society you have written "The reference clearly says that the Boeing 747 carries a relatively high cabin pressure (CP), or equivalently a relatively low equivalent cabin pressure altitude, than the Airbus A380." I must strongly disagree because it does not say that. What it does say is that at some undisclosed time in the recent past, Mr Seccombe of the Concord General Hospital in Sydney, Australia, and some of his colleagues, investigated the cabin pressure on 102 flights in airline aircraft manufactured by Airbus and Boeing. On 65 flights in the Boeing 747 they found a median CP of 838 hPa. On 8 flights in the Airbus A380 they found a median CP of 808 hPa.

It is true that 838 hPa is a greater pressure than 808 hPa, but Seccombe’s research most definitely does not allow anyone, and certainly not an encyclopaedia, to conclude that cabin pressurization in the Boeing 747 aircraft type is different to that in the Airbus A380 aircraft type. Such a statement would be an abuse of the available statistics. It is possible to investigate the relative design and performance of cabin pressurization in the 747 and A380 but it will require relevant information from reliable published sources. To begin with, I would like to know the certificated value of the maximum cabin differential pressure in the two aircraft types – that is not a figure subject to operators’ preferences or Captains’ flight planning. Alternatively, I would like to know the settings used by Airbus and Boeing for the pressure relief valves in the two aircraft types – those settings are also immune to operators’ preferences and Captains’ flight planning. Mr Seccombe’s research was adequate for his purposes and the purposes of the European Respiratory Society bit it wasn’t adequate for Wikipedia to make a comparison between two aircraft types, both of which now exist in their thousands (B747) and their hundreds (A380), and are operated by a large number of airlines over a great number of routes with significant variation in altitude and weather.

The section on “Aircraft” needs a lot of work to lift it to a suitable standard. Are you able to help? Dolphin (t) 06:12, 14 December 2015 (UTC)

I agree with your analysis. I should have said "may carry" or something along those lines. I happen to know that the A380 supports a maximum Pdiff of 9.2 PSI and the 747 supports 9.4 psi, but knowing and being able to cite a reliable source are two different things. And of course airlines can select any lower Pdiff by policy. I tweaked the language in the article. 71.197.166.72 (talk) 21:11, 16 December 2015 (UTC)

Reason for pressurization to be less than sea level pressure.

I don't think this article explains the reason to use a cabin pressure less than sea level. Does it really reduce stress on the airframe? Is it to save weight (several hundred kilos)? — Preceding unsigned comment added by 106.68.193.191 (talk) 03:03, 14 January 2016 (UTC)

The key parameter here is the cabin differential - the difference between the pressure inside the fuselage and atmospheric pressure outside the fuselage. The stress in the skin of the fuselage is determined by the cabin differential and the thickness of the skin. If a pressurized aircraft is designed and approved for a high cabin differential it must have thick skins, or skins made of stronger material than would be the case if it was designed and approved for a low cabin differential. So a compromise is required by the designer - does he select a high cabin differential for maximum passenger comfort and bear the cost of heavier weight or more expensive material; or does he select a low cabin differential for a lighter weight or less expensive material? A relevant consideration is that cabin altitudes less than about 8,000 feet cause no risk or discomfort to the great majority of able-bodied passengers. Do you think these considerations are adequately explained in the article? Dolphin (t) 07:41, 14 January 2016 (UTC)

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Aloha 243 cause

In the introduction, the article appears to mis-state the cause of the Aloha 243 incident. There was no pre-existing Boeing design limitation on number of cycles that the airframe was designed to endure. Boeing and Aloha both knew the cycles the aircraft had accumulated, and it was not out of specification. Rather, poor inspection and maintenance of the fuselage was the cause, which would have detected the fatigue cracks. If there is no objection, I will delete the Aloha 243 sentence from the introduction. --Westwind273 (talk) 16:39, 3 March 2022 (UTC)

Cylindrical cross-section?

The first image caption says, An airliner fuselage, such as this Boeing 737, forms a cylindrical pressure vessel. It's certainly true that most airliners are cylinders, but not all. Counter-examples include Airbus A380 and Boeing 377 Stratocruiser. We shouldn't be introducing (unsourced) new information in image captions which doesn't appear anywhere in the main text, and we shouldn't be implying that all airliners are cylinders. This needs a WP:RS and a better discussion. -- RoySmith (talk) 17:39, 24 July 2022 (UTC)

@RoySmith: You are assuming that a cylinder has, by definition, a circular cross-section. Your assumption is incorrect. As our article Cylinder makes fairly clear, a cylinder has at least a short length whose cross-section is uniform. Many cylinders have a circular cross-section but others have other cross-sections such as elliptical. Some books on the subject refer to simpler geometric cross-sections such as triangular cylinders, square cylinders, pentagonal cylinders.

When our article says that airliner fuselages are cylinders it is not saying they are circular in cross-section; it is saying that for the major part of the fuselage it’s cross-section is uniform, regardless of whether that cross-section is circular, elliptical, figure-eight or the composition of two or more basic curved shapes. Dolphin (t) 11:42, 25 July 2022 (UTC)

Yes, you are correct that I was thinking circular cross sections. But, we still need a WP:RS to support the statement that most airliners are cylinders, although there's exceptions to that too, i.e. Lockheed Constellation. -- RoySmith (talk) 13:18, 25 July 2022 (UTC)

I agree that the fuselage of the Constellation was slightly curved and therefore not a true cylinder. Despite that, the fuselage of the Constellation becomes increasingly stressed as the cabin pressure differential increases, just like any truly cylindrical pressure vessel.

Verifiability states that material must be attributed to a reliable, published source if its verifiability has been challenged, or is likely be challenged. Material that is highly unlikely to be challenged is not required to be sourced, as described at You don’t need to cite that the sky is blue. The article is not placing any emphasis on the cylindrical nature of the fuselage of most (all?) pressurised airliners and it is an unremarkable way to describe the fuselage of pressurised airliners so I am in favour of allowing this sentence to remain unsourced; similarly to any statement that the sky is blue. Dolphin (t) 13:49, 25 July 2022 (UTC)