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Question ID: 501224

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  • Question ID: 501224

    During the preparation for approach to Zurich airport (1416 ft/AMSL) a pilot hears the following message on the ATIS: "Inversion warning. Inversion of 12 deg between 1900 ft and 2300 ft altitude." This message indicates that the pilot should be prepared:

    A. For freezing precipitation below the inversion
    B. For fog below the inversion
    C. For wind shear just above the bottom of the inversion
    D. That the performance of the engine will be reduced from inversion level down to ground

    D is marked correct but why is C also wrong. Maybe I'm not understanding the bottom of inversion vs top of inversion?

    Thanks

  • #2

    This is a controversial question. Our problem with answer c is that we would expect the windshear at the top of the inversion, not the bottom. This makes answer d the only one that's correct, but it's somewhat unsatisfactory because the loss of engine performance in the last few hundred feet of the approach will hardly amount to a significant hazard.
    If answer c was worded "at the top of the inversion layer" it would be the best of the 4 answers, so if you get one of these questions in the exam I suggest you read it very carefully, in case the wording has been improved.
    Recent feedback from the exams on these inversion questions would be welcome, and, remember you are given the opportunity to comment on questions that you consider unsatisfactory at the end of your exam.

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    • #3
      It sounds like they are sticking to the rules of writing multiple choice questions. "Some of the answers can have correct elements, and even be scientifically correct but only one answer should stick out to those that have a true understanding". And yes I have recently been doing FAA Fundamentals of Instruction exams 😂😂

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      • #4
        I'd love a clarification here. What do you mean by the top or bottom of an inversion? I guess there is a point at which the temp stops decreasing and starts increasing and then another point at which the temp begins to decrease again. I would understand the inversion to be this band. And that you're saying that turbulance occurs mainly at the point where the temp starts to decrease again?

        Surely aircraft performance depends on both T and P - i.e. density altitude. Sure the air warms up as the aircraft decends, but the Pressure is also going up. Total effect (density altitute declining therefore increasing aircraft performance. I thought the issue with inversions was the drop in performance as you pass through the layer of warming air, because the aircraft is encountering air which is both reducing in pressure and increasing in T. I.e. a marked increase in density altitude for a small increase in true altitude.



        Surely here the impression is that the wind shear is at the bottom of the inversion?

        https://www.aviationweather.ws/046_Wind_Shear.php
        Last edited by mchristlieb; 11-09-2019, 18:11.

        Comment


        • #5
          A badly written EASA Q and set of answers. The bottom of the inversion is at 1900 ft and the top at 2300 ft. I would expect windshear just above 1900 ft as the warm air will be moving and "turbulent" compared to the stagnant cold air below; however, I would expect turbulence at the top of the inversion. The answer has been changed to the original windshear answer.
          BGS TKI

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