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You are flying in the mountains. Which error will occur with your altimeter due to the Venturi effect?
  • A
    The altimeter overreads. The wider the valley, the greater the error.
  • B
    The aircraft is higher than indicated. The effect decreases with decreasing wind speed.
  • C
    The altimeter overreads. The higher the wind speed, the greater the error.
  • D
    If you are flying with a tailwind, the altimeter underreads; if you are flying with a headwind, it overreads.
The mountains will create a sort of Venturi ‘throat’ that will make the wind to converge between the valleys. Therefore, the wind speed will increase, and the pressure will drop. A decrease in ambient pressure will make the altimeter over-read as the aircraft’s true altitude will be actually lower.
 

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