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The alternate static source of a light non-pressurized aircraft is located in the flight deck. As the alternate static source is opened, the vertical speed indicator may…

  • A
    be blocked.
  • B
    indicate a high rate of descent.
  • C
    indicate a momentary climb.
  • D
    indicate a slight momentary descent.
Due to the motion of the aircraft in flight, the relative airflow will be accelerated over the fuselage, creating a lower static pressure. This means that the air pressure all around the aircraft is slightly lower than inside. In case of venting of the back-up static source located in the cockpit, air from the cockpit (from high pressure) will flow outside (to lower pressure) => aerodynamic suction. This will cause the pressure in the cockpit to decrease and become lower than the static pressure around the aircraft and will cause the following:
  • Altimeter over reads.
  • Airspeed over reads.
  • VSI indicates a momentary climb.

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