The term uncontrolled decompression here refers to the unplanned depressurisation of an aircraft cabin at high altitude. Decompression can occur due to structural failure of the pressure vessel, or failure of the compression system itself. The speed and violence of the decompression is affected by the size of the aircraft, the differential pressure between the inside and outside of the vessel and the size of the leak hole.

The Federal Aviation Administration recognizes three distinct types of decompression events in aircraft:

• Explosive decompression

• Rapid decompression

• Gradual decompression

\"\"First cases of explosive decompression took place in 1954 when two De Hevilland Comet-1 exploded en-route. Since it was the first jet passenger airliner, constructors made several mistakes when designing the aircraft’s cabin with square illuminator holes and too thin skin, suffering from metal fatigue. Although designers learned a very good lesson from that tragedy, about 30 catastrophies are connected with metal fatigue.
\"\"For example the notorious case with Aloha’s Boeing 737-200 in 1988, when the aircraft, flying at 7000m, suffered the loss of top of its fuselage. It was a miracle, but the pilots managed to perform a safe landing. Although everyone on board got serious medical problems, only one flight attendant died, falling out of the plane. Also the gradual decompression is no less dangerous.
\"\"Helios Airways Boeing-737 crashed into a mountain on 14 August 2005, north of Marathon, Greece. The aircraft was not pressurized after departure due to improper maintanence work. That fact was not noticed by the pilots. A lack of oxygen incapacitated the crew, leading to the plane\’s eventual crash after running out of fuel.