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Thread: Transponder malfunction

  1. #1
    Senior Member Dave S's Avatar
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    Oct 2008
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    St Paul, MN
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    1,833

    Default Transponder malfunction

    Good afternoon,

    This weekend, when working with a towered airport, I found that my transponder was reporting altitude approximately 35% higher than the altimeter. The local antenna farm provides a solid reference for confirming the altimeter - and that was OK. The controller was kind enough to do some readings at different altitudes and the error seems to be a percent of scale error. All previous biennial calibrations have come out right on the money.

    I have the plane grounded till I can schedule a trip to an avionics shop (home airport sits under a Class B); however, has anyone else had this kind of problem and how costly is it to resolve? Is this likely to be the transponder; or the encoder, or both?

    Transponder is a Garmin 320A new at installation and the encoder is a Ameri-king , also new at installation.

    Thanks for your input - transponders are pretty much voodoo in my little world.

    Dave S
    KF7 Trigear
    912ULS Warp

  2. #2
    Senior Member Av8r_Sed's Avatar
    Join Date
    Feb 2010
    Location
    10C Greenwood, IL
    Posts
    671

    Default Re: Transponder malfunction

    I doubt it's the transponder. Most likely the encoder or a bad wire connection between the two. It should be pretty easy for the tech to track down once a calibrator is hooked up.
    -- Paul S
    Model III SN910
    582 IVO Med

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