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Assuming cabin pressure decreases, the cabin rate of climb indicator should indicate
  • A
  • B
    a rate of descent of approximately 300 feet per minutes.
  • C
    a rate of descent, dependent upon the cabin differential pressure.
  • D
    a rate of climb.

Refer to figure.

Cabin Rate of Climb Indicator. Similar to VSI, is sensitive to rates of change of pressure and indicate the rate of change of cabin (apparent) altitude in an aircraft’s pressurized cabin.

  • When it shows a rate of climb: it means that the cabin altitude is increasing => at a higher altitude, pressure decreases => therefore, the pressure inside the cabin is reducing;
  • Conversely, when it indicates a rate of descent: it means that the cabin altitude is decreasing => at a lower altitude, pressure increases => therefore, the pressure inside the cabin is increasing.

Cabin altitude. Cabin pressure in terms of equivalent altitude above sea level.
Differential pressure. The difference in pressure between the pressure acting on one side of a wall and the pressure acting on the other side of the wall. In aircraft air-conditioning and pressurizing systems, it is the difference between cabin pressure and atmospheric pressure.

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