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Cross Country planning

Asked by: 446 views General Aviation, Instrument Rating, Private Pilot

HI

Im trying to make xc country planning. My question is to calculate my TAS at cruise altitude do I have to find pressure altitude at my cruise altitude? or I can use the pressure altitude at field ?

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1 Answers



  1. KDS on Oct 28, 2017

    The way your question is worded, I’m not 100% sure if you are asking about when you are planning the flight or while you are in flight, so I’ll take a stab at answering both.

    For planning the flight, the tables in the POH will give you the TAS for various conditions. One of the conditions is pressure altitude. To determine pressure altitude, you can use the altimeter setting and your planned flight altitude (indicated altitude). Most people will just take their planned altitude and use that as pressure altitude.

    If you’re trying to calculate your TAS while you’re in flight, you will need four pieces of data.
    (1) The altimeter setting.
    (2) Your indicated airspeed
    (3) The OAT
    (4) Your indicated altitude

    The altimeter setting and the indicated altitude (1) and (4) are just to determine pressure altitude. So, to make it simple, just put 29.92 in the Kollsman window of your altimeter and read what it says for altitude. That is your pressure altitude.

    Then with (2) and (3) and the pressure altitude, you can enter that on an E6B or electronic device and get the TAS.

    You wouldn’t want to use the pressure altitude at the field for anything related to cruise performance because that is thousands of feet below where you’re operating. I think what you’re really asking there is if you should use the altimeter setting at the field.

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