What does decompression mean in flight terminology?

• A. The reduction of altitude during flight.
• B. The process of removing ice from aircraft surfaces.
• C. When the cabin pressurization system has failed and the atmosphere inside the aircraft equals the air outside the aircraft.
• D. The delay of a flight due to schedule.

Answer: (C)

Decompression means the cabin pressurization system fails and the atmosphere inside the aircraft equals the air outside the aircraft. In flight, the cabin is kept pressurized to a lower altitude than the outside air to provide breathable conditions. When that pressurization is lost, the interior air rushes toward the outside, the cabin altitude rises, and supplemental oxygen may be needed. This is different from simply descending as part of a planned flight, removing ice (de-icing), or delays due to schedule, which are unrelated to a loss of cabin pressure.