Uncontrolled decompression

The sudden pressure drop in a pressurized airplane cabin is the rapid drop in air pressure in the aircraft cabin with alignment to the outside of the aircraft time as determined by the current pressure altitude. It provides an air emergency, since, depending on altitude there is an acute suffocation and Hypothermiegefahr for the flight crew and the passengers.

Causes

The technical device of the pressurized cabin of the car interior from the environment is kept under pressure at flight altitudes, where there is no human survival more because of the low air pressure possible. The pressure in the aircraft pressure is because the car is not designed to, among other reasons of weight for any high pressure differences, but less than the air pressure at sea level and corresponds in a commercial aircraft typically the air pressure ft at a height of about 2,500 m or 8,200 prevails. .

, An undesirable drop in the cabin pressure can be performed at different speeds. The U.S. Federal Aviation Administration FAA has in this respect a three possible types: Explosive decompression in less than half a second, fast and slow decompression. The causes of human error, a technical defect in the regulation of the pressure or damage to the aircraft fuselage through fatigue, explosion, fire, failure of windows, doors or pressure bulkhead come into question.

Follow

By a sudden drop in pressure in the aircraft cabin, it comes according to the gas laws for intense cooling of the interior with the result of the condensation of atmospheric humidity and a formation of fog in the cabin. Is the fuselage open, it should be noted that the temperature in a typical cruising altitude of 10,700 m or ( rounded) 35,100 feet is only -54 ° C.

The consequences for humans relate to crew and passengers alike. It comes first, by the expansion of air or gases into body cavities for forming Barotraumata. Pain in the middle ear, sinuses, carious teeth can be the result. Even gas-filled bowel loops naturally increase their volume. Second, the rapid drop in pressure cause decompression sickness. In the blood of dissolved nitrogen can be liberated and the gas bubbles can lead to embolism. Third, the acute lack of oxygen is dangerous because the oxygen in the air is no longer sufficient to meet the oxygen needs of the body. The human body has no reserves for oxygen; the oxygen saturation of the blood therefore falls quickly, depending on the height at which it came to the event to life-threatening levels. The brain as a sensitive especially for oxygen deficiency organ reacts rapidly with a limitation of consciousness to unconsciousness.

In contrast to the high-altitude mountaineering, the change in oxygen saturation occurs abruptly and acclimatization does not occur. From the fact that healthy, trained mountaineers at altitudes of 8,000 m are still capable of action can not therefore be concluded that crew members and passengers in the event of such an event, the air pressure on, be quasi abruptly catapulted several thousand feet up, and thus - depending on age and health - may be restricted.

The time that still remains the that person to meaningful action is called the time of useful consciousness (TUC ) or Effective Performance Time ( EPT). This time will be shorter depending on the altitude. At a flight level of 250, ie 25,000 feet, the TUC is not provided with three to five minutes at a flight level of 350 ( 35,000 feet ), however, only 30 to 60 seconds. From a surprise or action by blocking panic is here no talk. Flight levels above 300 and up to 510 ( 15,545 m) can be achieved for example with Learjet. At a flight level of 500 remain only nine to twelve seconds to meaningful action. The faster the decompression occurs, the shorter the time available and is reduced during fast decompression and flight levels over 400 to less than ten seconds.

Measures in case of emergency

Commercial aircraft are fitted above each seat and also in the toilets with oxygen masks, which are located in the cabin ceiling and at a pressure drop automatically by opening the flaps fall into the field of view of the passengers. Only through the mask to the passenger train down the oxygen supply is activated. This mechanism prevents the uncontrolled discharge of the oxygen, thus reducing the risk of fire, and helps to protect the limited oxygen reserves. Given the shortness of the time available to each passenger who noticed the dropping of the masks should immediately put on a mask and only then help neighboring passengers. A reverse action sequence would involve the risk that the helper himself unconscious and thus would provide assistance any other person incapable. In anticipation of the upcoming descent has the passenger, if not already done, to buckle up. The taking of the Brace position is advantageous. The table stowed in the airplane seat in front of him and vertically, of their own rest are the usual measures in anticipation of an emergency landing. The procedure at a pressure drop on the plane, since by law, explained before the start of a flight by flight attendants, which also video screenings are taken to help. The security information stored in the pocket of the airplane seat contains these instructions also.

Pilots must first measures put their own oxygen masks, an emergency descent (german emergency descent ) perform in the steep descent to sink to an altitude of 10,000 feet, and over the air traffic control declare the emergency. Such an emergency descent to act on the passengers as a " crash ", but is a controlled flight. At this altitude, the air is unbreathable again thanks to the higher air pressure. The maximum allowable airspeed must not be exceeded. To support the air brakes (if any ) extended. Air traffic control is informed by the sudden change of altitude. In consultation with the air traffic control can be carried out an emergency landing.

If the pilot unconscious, may be the result, that the autopilot altitude and course maintains and the aircraft continues to fly until failure of the engines by fuel shortages. The death of Payne Stewart is attributed to such an event.

Frequency and examples

From the perspective of the individual passenger, a dangerous loss of cabin pressure is an unlikely situation. However, it is used in the whole of the aeronautical repeatedly such incidents. Pilots and flight attendants are trained to meet them. The Aeromedical Society of New Zealand was in 2000 by an annual 40 to 50 such events around the world.

As tragic examples of a crash due to a pressure drop among other things, the Helios Airways flight 522 and the Turkish Airlines Flight 981 are the British Airways Flight 5390, Aloha Airlines Flight 243 and the emergency landing of a Boeing 737 in Limoges however, on 25 August 2008 are examples of a successfully coped with such a situation. What in the press, the emergency landing in Limoges concerning, as " sagging " of the aircraft was described to 8,000 meters, was actually the lifesaving emergency descent. The passengers described later a sharp temperature drop in the machine and complained of nose and throat pain.