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3 Answers

AWOS given Altimeter pressure lower than airport elevation

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Weather

Hi,

While setting my altimeter setting according to what was given by my local airport AWOS, I realized that the altimeter reading displayed is lower than the official ground elevation of the airport I am flying from.

Is that normal? What do I need to take note of when flying to ensure I don't go too low to the ground than I would like to.

Thank you.

3 Answers



  1. stillkicking on Jan 24, 2022

    Generally speaking and the way I was taught… you set the altimeter to the actual height of the airport (elevation) prior to take off.

    Once airborne and as you can pick up the AWOS for airports on your route or that are close by you can reset to that.

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  2. Bryan on Jan 24, 2022

    Altimeters are very sensitive and need calibration and maintenance from time to time. If you are planning an IFR flight, the altimeter has to read plus or minus 75 of field elevation. So a negative value is possible.

    When the altimeter is checked on its regular cycle, the person performing the check has a table of tolerances based on the equivalent pressure and the tolerances range from 20 feet at low altitudes up to nearly 300 feet at 50,000.

    If your altimeter reads more than 75 feet below field elevation when you’re on the ground, I personally would not fly that aircraft until a mechanic has taken a look. If it’s within 75 feet, take note of the difference between the reading and the field altitude and keep that difference in mind for the rest of your flight. An altimeter error of <75 feet should not be an issue except on takeoff or landing.

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  3. Russ Roslewski on Jan 24, 2022

    Another consideration – the official Airport Elevation is the highest elevation on any of the runways at the airport.

    Even at flatland airports, it’s not uncommon for there to be 20 feet or more of elevation difference between the runway ends, or between the runway and the parking ramp. I just checked a local airport here in Oklahoma (PWA) – the “Airport Elevation” is 1300 and the threshold elevation for runway 13 is 1270. From personal experience, the parking ramps are quite extensive and certainly have quite a bit of elevation change.

    Another random lookup – at Reno/Stead (RTS), Field Elevation is 5050, which is at the end of runway 26. But the end of runway 8 is 4992 – 58 feet of difference on a 7608 ft runway.

    For airports with an official FAA airport diagram (mostly Class D or larger), this information is readily available from that diagram. Otherwise, approach charts can give you some of that information. Another source would be Google Earth, which has pretty accurate elevation data as you scroll around.

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