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  • Q711320

    Perhaps a question that better suits "Instrumentation", but anyway:
    Why would the indications of engine power and attitude be affected by a pitot / static / aoa blockage?
    Engine power would be indicated as N1 / RPM / MAP, and attitude on the ADI which uses the suction system, is that not right?
    TY

  • #2
    you're not alone, i'm also confused with this one...

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    • #3
      LO 071 02 02 Icing Conditions is where this is from. The reference is ICAO DOC 9640, where it says:
      Ice forming on pitot tubes and static ports or on angle of attack vanes may give false attitude, airspeed, angle of attack and engine power information for air data systems.

      If you google air data system inputs and outputs you will find some useful diagrams which may help. Also think of the Air France A330 over the South Atlantic in icing conditions, the crew were completely confused with indications.

      The question of course is from feedback, so the wording is uncertain - but I guess I would go with all of them.

      Tom

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      • #4
        Thanks Tom.

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        • #5
          Just encountered this question...

          I can't see how icing on AoA vanes or pitot/static ports would affect an attitude indication, whether the attitude system is vaccuum powered or derived from an INS/IRS. I can agree that icing on the AoA vane would cause an incorrect AoA indication and thus potentially cause false AoA-derived readings to be displayed on the ADI (for example, false pitch eyebrows for maximum alpha). However, I don't see how the actual indicated attitude would be wrong. I would also have thought that ADC data would indeed be affected by icing, so not sure why answer 5 is excluded.

          Are we sure that this hasn't been misread as altitude? I can most certainly see that being affected by icing on the static port.

          So I get 2,3,4,5

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          • #6
            This question has been causing a worry for quite some time! The wording we have at the moment is based on feedback, but if you have just encountered this in your exam you might have suggestions for an update. The question reference is from ICAO Doc 9640 (The Manual of Aircraft Ground De-Icing/Anti-Icing operations). The statement in Chapter 1 (Introduction) tells us:

            Ice forming on pitot tubes and static ports or on angle of attack vanes may give false attitude, airspeed, angle of attack and engine power information for air data systems.

            This statement is introducing the Clean Aircraft Concept, it goes on to say: It is therefore imperative that take-off not be attempted unless it has been ascertained that all critical surfaces of the aeroplane, as well as all instrument probes, are free of adhering snow, frost or other ice formations. This vital requirement is known as the Clean Aircraft Concept.

            It is important to understand that Ice forming on pitot tubes and static ports or on angle of attack vanes may give false attitude, airspeed, angle of attack and engine power information for air data systems, they do not mean false attitude information for your attitude indicator in the cockpit.

            So, if you can remember a more accurate wording that would be great - we really try to get these questions as close as we can to the exam version!! I acknowledge that the current wording is less than ideal, but that is as close as we have at the moment.

            Thanks

            Tom

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