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Altimeter setting error for ILS approach

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Commercial Pilot, General Aviation, Instrument Rating, Student Pilot

1.Today if I doing an ILS approcah(Elevation of touchdown zone is 500ft MSL,DA(H) is 200ft  AGL),and ATIS report pressure setting is 30.42;unfortunately my altimeter is remain at 29.92 and can not  be change.the original DA is 700ft MSL(500+200).What is my new DA(H)? 

 

2.Today if I doing an ILS approcah(Elevation of touchdown zone is 500ft MSL,DA(H) is 200ft  AGL),and ATIS report pressure setting is 29.42;unfortunately my altimeter is remain at 29.92 and can not  be change.the original DA is 700ft MSL(500+200).What is my new DA(H)? 

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3 Answers



  1. Kris Kortokrax on Dec 11, 2014

    If your altimeter cannot be set to the current altimeter setting (a sensitive altimeter), you will not be flying an ILS approach.

    91.205(d) requires a sensitive altimeter for instrument flying.

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  2. Best Answer


    Russ Roslewski on Dec 11, 2014

    I read the question almost as if the altimeter is broken sometime in flight (a rare event certainly), but Kris is right that if this was a problem before takeoff you shouldn’t be flying IFR anyway.

    However, assuming that’s it’s really just a standard written test question asking you about altimeter errors and pressure changes, then it works like this:

    Each inch = about 1000 feet of indicated altitude. Since your altimeter is 0.5 inches off, that’s about 500 feet. The questions above are just opposites of each other, so in one case it’ll read 500 feet high, in the other, 500 feet low. We just need to figure out which.

    I tend to think of these type of questions from the cockpit view and turning the knob on the altimeter. If you turn it right/higher pressure, the altitude displayed goes up, which makes sense. So, sit there in your hovering aircraft at DA at the real 700 MSL and adjust the altimeter setting.

    In question #1, If you had the altimeter set correctly at 30.42 it would read 700 MSL at DA. But now take that knob and adjust it down to 29.92. Your indicated altitude is going to go DOWN by 500 feet, to 200 MSL.

    So the answer to your first question, if I understand the intent correctly, is 200 MSL.

    It’s the opposite for the second question.

    If I got the scenario or the intent of the question wrong, please let me know and I’ll adjust my answer.

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  3. Anton Dotti on Dec 12, 2014

    Russ is correct. However, if 29.92 remains in the Kollsman window, the altimeter will read pressure altitude, not altitude AMSL. Don’t confuse those two unless it’s a standard day.

    200 ft PA the first question and 1200 ft PA in the second, when at the DA of 700 ft AMSL.

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