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7 Answers

Pressure Altitude Without an Altimeter Setting

Asked by: 4609 views Student Pilot, Weather

Is there a way to calculate pressure altitude at home before a flight if my airport doesn't report an altimeter setting?

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7 Answers

  1. Best Answer


    ayavner on Jan 24, 2019

    Not really – you need that number to compare to standard (29.92″) so that you know how much to adjust up and down. You could probably get close if there is a forecast for that area that will provide that, but it may not be accurate at the time of the flight.

    As far as how to calculate it, it is about 1000′ per inch. So as an example if it is supposed to be 30.02″ tomorrow – then just take (29.92 – 30.02) * 1000 then add or subtract the result to the elevation. Higher pressure than standard means the PA will be lower than elevation, lower pressure means the PA will be higher. In this example,

    (29.92 – 30.02) = -.1

    -.1 * 1000 = -100′

    Elevation – 100′ = PA.

    Main thing to remember is the higher/lower relationship so you know what to expect and if your answer makes sense.

    Hope that helps?

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  2. KDS on Jan 24, 2019

    You can make a good guess of it if there are nearby airports.

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  3. Ticen on Jan 24, 2019

    Or to make it even simpler: every 100′ = .10 adjustment on Kollsman window (where you adjust altimeter setting). Increase .10, altimeter adjusts + 100, decrease .10, adjusts – 100′

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  4. John D Collins on Jan 24, 2019

    What are you using pressure altitude for? If all you are doing is determining the altimeter setting, when you get to the airport, set the altimeter to field elevation by adjusting the kollsman setting. If you have other needs for pressure altitude, set the altimeter setting to 29.92 and read the altitude to get the local pressure altitude.

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  5. ayavner on Jan 24, 2019

    He may need it as a starting point for the chase charts for takeoff/landing performance?

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  6. DarthDecker on Jan 24, 2019

    Yeah I was just trying to get it for my performance charts and all that stuff from home.

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  7. Kris Kortokrax on Jan 25, 2019

    I just looked at info for my home on the Weather Channel. It lists the barometric pressure and the temperature (all you need to calculate pressure or density altitude).

    You should be able to find the same info for your airport. If it is off by a tenth, that is a 100′ difference which will make no significant difference in the performance of your aircraft.

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