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Lower Pressure, Lower Altitude

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Aircraft Systems, General Aviation, Weather

Question posted on http://www.boldmethod.com/blog/quizzes/2016/09/systems-questions-are-easy-or-not/

Q.  You're sitting on the ramp, your altimeter is set to 30.47" Hg, and it reads 1500 feet. You pick up ATIS, and the latest altimeter setting is 29.97". You enter the setting on your altimeter. What elevation does it read now?

A. When you dial the Kollsman window to a lower Hg setting, the altimeter will decrease altitude. Since you're reducing it by 0.5 in Hg, it will decrease 500'.

Pressure decreases as altitude increases, why doesn’t the altimeter increase & read 2,000'?  Thank you for help understanding the logic.

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1 Answers



  1. crossaint on Sep 13, 2016

    Because the ATIS and actual pressure are the same 29.97inHg. The altimeter, being set to 30.47, senses 0.5inHg negative, which is good for 500′ height.
    When being corrected this pressure difference becomes zero and so does the 500′ additional height

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