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2 Answers

Blocked Pitot / Static Drain Hole

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Aircraft Systems, Instrument Rating, Student Pilot

If the drain hole is blocked but the inlet remains open how will your pitot/static instrument be effected and why?

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2 Answers

  1. Nathan Parker on Jun 10, 2011

    The textbook answer is that it shouldn’t affect any of the instruments.  The only time the drain hole blockage has any effect is when it’s combined with an inlet closure.  When the inlet is closed, the status of the drain hole controls whether the total pressure in the pitot tube is maintained, or drops to ambient static pressure (or less).
    I would bet, though, if we had instruments sensitive enough, we’d see a small gain in total pressure with the drain hole closed, with a minute gain in indicated airspeed.

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  2. Wes Beard on Jun 10, 2011

    Nathan is correct!  I would like to add to the discussion the purpose of the drain hole.  Originally designed to allow water and other small FOD (foreign object debris) to escape the pitot system so that normal operation would not be impeded. 
    With that in mind, a blocked pitot drain hole won’t have any effect initially on the flight instruments.  Over time water and FOD will block the pitot ram air input causing erroneous airspeed indications.

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