Pressure drop in the airplane

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The sudden drop in pressure in an aircraft with a pressurized cabin is the rapid drop in air pressure in the aircraft cabin, equalizing the pressure outside the aircraft and determined by the current flight altitude . It represents an air emergency because, depending on the flight altitude, there is an acute risk of suffocation and hypothermia for the aircraft crew and passengers.

In addition, explosive decompression can also pose a risk to the aircraft structure. In this case, the sudden drop in pressure is triggered by damage to the aircraft fuselage. During the process, electrical, mechanical and hydraulic lines can be damaged, and in the worst case, the aircraft can be completely uncontrollable.

causes

Due to the technical device of the pressurized cabin, the cabin interior is kept under overpressure in relation to the environment at flight altitudes at which human survival is no longer possible due to the low air pressure. The pressure prevailing in the aircraft is lower than the air pressure at sea ​​level , since the cabin is not designed for arbitrarily high pressure differences, among other things for reasons of weight, and in a commercial aircraft typically corresponds to the air pressure at an altitude of around 2,500 m or 8,200 ft . prevails.

An undesired drop in the cabin pressure can occur at different speeds. The American Federal Aviation Administration (FAA) divides this into three possible types: explosive decompression in less than half a second, fast and slow decompression. Possible causes are human error , a technical defect in the regulation of the pressure or damage to the aircraft fuselage due to material fatigue , explosion , bombardment, failure of windows, doors or pressure bulkheads .

consequences

Without structural impairment of the aircraft

In accordance with gas laws, a sudden drop in pressure in the aircraft cabin results in a strong cooling of the interior, with the result that the humidity in the air condenses and fog forms in the cabin. If the aircraft fuselage is open, it must be taken into account that the temperature at a typical cruising altitude of 10,700 m or (rounded) 35,100 feet is only −54 ° C.

The consequences for humans affect crew and passengers alike. On the one hand, the expansion of air or gases in body cavities leads to the formation of barotraumas . Pain in the middle ear , the paranasal sinuses , carious teeth can be the result. Gas-filled intestinal loops naturally also increase their volume. Second, the rapid drop in pressure can cause decompression sickness . Nitrogen dissolved in the blood can bubble out and the gas bubbles can lead to embolisms . Thirdly, acute oxygen deficiency becomes dangerous because the oxygen partial pressure in the air we breathe is no longer sufficient to meet the body's need for oxygen. The human body has no reserves for oxygen ; the oxygen saturation of the blood therefore quickly falls to life-threatening levels, depending on the level at which the event occurred. As an organ that is particularly sensitive to a lack of oxygen, the brain reacts quickly with a restriction of consciousness up to and including unconsciousness .

In contrast to high-altitude mountaineering , the change in oxygen saturation occurs suddenly and acclimatization does not take place. From the fact that healthy, trained mountaineers are still able to act at heights of 8,000 m, it cannot therefore be concluded that crew members and passengers will be catapulted several thousand meters upwards almost suddenly in the event of such an event, regarding the air pressure, and thereby - depending on age and state of health - can be restricted.

The time that those affected still have to act meaningfully is called time of useful consciousness (TUC) or Effective Performance Time (EPT). This time is shortened depending on the flight altitude. At a flight level of 250, i.e. 25,000 feet, the TUC is specified as three to five minutes, but with a flight level of 350 (35,000 feet) it is only 30 to 60 seconds. There is still no talk of a moment of surprise or the blocking of action by panic . Flight areas of over 300 and up to 510 (15,545 m) can e.g. B. can be achieved with Learjets . With a flight level of 500, there are only nine to twelve seconds left for meaningful action. The faster the decompression occurs, the shorter the time available and with faster decompression and flight levels over 400 seconds it is reduced to less than ten seconds.

With damage to the aircraft

In the case of a damaged aircraft fuselage, such a violent, explosive pressure drop can occur that important structures of the aircraft are destroyed. The following scenarios, for example, have occurred in aircraft accidents:

  • In the accident on Turkish Airlines flight 981 , a cargo door of a DC-10 was not properly locked; the poorly designed locking mechanism contributed to this. The sudden drop in pressure in the cargo hold caused the floor of the passenger cabin to yield to the pressure difference. In the process, all control cables that run from the cockpit directly below the cabin floor to the stern were damaged. The plane crashed near Paris, all 346 people on board were killed. This accident contributed to the fact that nowadays all passenger aircraft must have pressure equalization between the passenger and cargo compartments in order to prevent the floor from collapsing. (1974, worst aircraft accident to date)
  • In Japan Airlines Flight 123 (1985, vertical stabilizer breaks) and China Airlines Flight 611 (2002: fuselage breaks, all 225 dead), improperly carried out repairs to a Tailstrike damage resulted in an explosive pressure drop years later led to the crash. Flight 123 is to date - with 520 fatalities - the most serious accident in which a single aircraft was involved.
  • In two accidents involving the De Havilland DH.106 Comet in 1954 - BOAC flight 781 and South African Airways flight 201 , progressive, construction-related material fatigue was found, which appeared on a window. Both planes crashed due to an explosive pressure drop.
  • On Saudia Flight 162 , a blown tire during flight caused a hole in the cabin floor. The sudden drop in pressure caused two children on board to be torn from the aircraft. (1980)
  • An engine exploded during a flight of a Boeing 737 from New York (LaGuardia) to Dallas in April 2018. At least one part of the engine broke through a window and injured a passenger seated there, who was sucked in by the cabin air that then escaped through the window opening and was held back by other passengers. Emergency landing in Philadelphia, 1 death, several slightly injured.

Actions in an emergency

opened compartment with the oxygen masks in the passenger cabin

Commercial aircraft are equipped with oxygen masks above every seat and also in the toilets , which are located in the cabin ceiling and automatically fall into the passenger's field of vision when the pressure drops by opening the flaps. The oxygen supply is only activated when the mask is pulled towards the passenger. This pulling on a rip cord ignites the chemical oxygen generator and starts the production of oxygen. This chemical oxygen generator is attached directly above the masks under a cover and can deliver almost 100% pure oxygen gas for approx. 12 to 15 minutes. Since at an external pressure like at 10 km flight altitude with normal breathing air with approx. 21% oxygen content in approx. 15 seconds unconsciousness due to lack of oxygen occurs, every passenger who notices the falling of the mask should put on a mask immediately and only then help neighboring passengers and clarify the situation in his environment. The oxygen mask does not compensate for the pressure drop in the cabin, but under the mask the partial pressure of oxygen is increased. This allows the lungs to absorb enough oxygen even at low pressure.

In anticipation of the impending descent, the passenger has to buckle up , if not already done . It is recommended to take the brace position . Folding the table in the aircraft seat in front of him and putting your own backrest upright are the usual measures when expecting an emergency landing. The procedure in the event of a pressure drop in the aircraft, as required by law, is explained by the flight attendants before the start of a flight , with video demonstrations also being used as an aid. The safety information in the pocket of the aircraft seat also contains this information.

The pilots have to set up the first measures their own oxygen masks, an emergency descent ( english emergency descent carry) in the steep descent to decline km to an altitude of 3, and compared to the air traffic control to declare an emergency. Such an emergency descent can have the effect of “falling” for the passengers, but it is a controlled flight. At this altitude, the air with a low oxygen content can be breathed again thanks to the higher air pressure. The maximum permissible airspeed must not be exceeded. The air brakes (if present) are extended to assist . A preferred landing can then be carried out in consultation with air traffic control .

If the pilots become unconscious, the result can be that the autopilot maintains altitude and course and the aircraft continues to fly until the engines fail due to a lack of fuel. Payne Stewart's death is attributed to such an event.

Frequency and examples

From the perspective of the individual passenger, a dangerous drop in cabin pressure is a rather unlikely situation. However, incidents of this kind occur time and again in aviation as a whole. Pilots and flight attendants are trained to face them. The New Zealand Aeromedical Society estimated 40 to 50 such incidents worldwide in 2000.

The tragic examples of a crash due to a drop in pressure include Helios Airways flight 522 and Turkish Airlines flight 981 . The British Airways Flight 5390 , Aloha Airlines Flight 243 and the emergency landing of a Boeing 737 in Limoges on 25 August 2008, however, are examples of issues successfully dealt with such a situation. What was described in the press as the "sagging" of the aircraft by 8,000 meters in relation to the emergency landing in Limoges was actually the life-saving emergency descent. The passengers later described a sharp drop in temperature in the aircraft and complained of nose and ear pain.

See also

Individual evidence

  1. ↑ a b Jochen Hinkelbein, Michael Dambier: Aviation medicine and aviation psychology for private pilot training . aeromedConsult Hinkelbein Dambier GbR, Hördt 2007, ISBN 978-3-00-020097-7 , p. 78 .
  2. ^ Peter Bachmann: Aviation medicine for pilots and passengers . Motorbuch Verlag, Stuttgart 1999, ISBN 3-613-01970-1 , p. 175 .
  3. ↑ a b AC 61-107A - Operations of aircraft at altitudes above 25,000 feet msl and / or mach numbers (MMO) greater than .75. (PDF; 143 kB) Federal Aviation Administration , July 15, 2007, pp. 13, 20 , accessed on November 13, 2010 (English).
  4. ^ Peter Bachmann: Aviation medicine for pilots and passengers . Motorbuch Verlag, Stuttgart 1999, ISBN 3-613-01970-1 , p. 22 .
  5. ↑ Aero Courier. Retrieved November 12, 2010 .
  6. ↑ One dead after engine failure on US passenger aircraft orf.at, April 18, 2018, accessed April 18, 2018.
  7. ↑ Günter Schönweiß: Human performance. Human Factors in Aviation. Exam questions and answers for PPL . (PDF; 2.0 MB) (No longer available online.) Formerly in the original ; Retrieved November 14, 2010 .  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Toter Link / www.sky-doc.de  
  8. ↑ Rapid Decompression in Air Transport Aircraft. (PDF, 37 kB) Archived from the original on May 25, 2010 ; accessed on December 19, 2010 (English).
  9. ↑ Injured during an emergency landing of a Ryanair plane. In: Welt online. Retrieved November 13, 2010 .
  10. ↑ Aerosecure: Ryanair emergency landing in Limoges . Retrieved November 13, 2010 .
  11. ↑ A drop in pressure forces the Ryanair plane to dive - many injured. In: Spiegel online. Retrieved November 13, 2010 .