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Malfunctioning of the automatic pressurization system is indicated by:

1) a change in environmental sounds.
2) the cabin altitude gauge indicates an abnormal rate of climb.
3) the differential pressure between the exterior and the interior of the aircraft decreases.

The combination regrouping all the correct statements is:

  • A
    1, 3
  • B
    1, 2
  • C
    2, 3
  • D
    1, 2, 3

CABIN DECOMPRESSION

Although cabin pressurization systems are highly reliable, malfunctions do occur with system components or aircraft structures. Of the malfunctions that can occur, cabin decompression is the most serious. The loss of pressurization can be slow - in case of a small air leak - while a rapid or explosive decompression occurs suddenly, usually within a few seconds.

Slow decompression involves a very gradual decrease in cabin pressure and it may be the result of a faulty door seal, a malfunction in the pressurization system, or a cracked window. Slow decompression may not always be obvious. In some cases an unusual noise, such as whistling or hissing sound around the door areas, may be an indication of a slow decompression, therefore the flight crew should be notified immediately. One of the first physiological indications of a slow decompression may be ear discomfort or ‘popping’, joint pain, or stomach pain due to gas expansion.
The cabin altitude will tend to equal the aircraft altitude, cabin altitude increases and the pressure inside the cabin decreases. As a result, the differential pressure (between the cabin and the outside) decreases and the Cabin Altitude rate of climb indicator will show a climb.
Explosive decompression is likely to occur when a large part of the cabin structure fails. Windshield, cabin windows, and door failures are typical causes of explosive decompressions. Rapid/explosive decompression is dramatic and, in many cases, can be recognized by the following signs:
  • A loud bang, thump or clap that is the result of the sudden contact between the internal and external masses of air;
  • The cabin fills with fog/mist due to the immediate condensation of water vapour in the cabin;
  • Rush of air, as the air exits the cabin;
  • After the decompression, the cabin is extremely cold because most of the heated air is drawn out and the remaining air cools as it expands;
  • The release of the cabin oxygen masks, when the cabin altitude reaches 14 000 feet.
If a breach in the aircraft structure is the cause of the decompression unsecured items in the immediate area are ejected from the aircraft, debris may fly around the cabin, loose items may become projectiles and dust particles may limit visibility.

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