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Thread: Wrong speed for plane

  1. #1
    Passenger fl95's Avatar
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    Jul 2018
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    Question Wrong speed for plane

    Hi,
    my VAN'S RV6 is equipped with a fresh updated FUNKE TRT800H Transponder and a Garmin 496 GPS sends the ADS-B Data to the Transponder.

    I can see my flights very well in FlightRadar24, altitude is okay, but my flying speed is wrong. My real speed is between 110 and 150 Knots but Flightradar History shows wrong Speeds between 110 and 515 Knots ????
    Is it a Transponder Problem ? Last Year I had no ADS-B out and the plane was sometimes visible with MLAT, but with correct speed.

    Search for PH-CRJ in flightradar24. (I am not allowed to post Link)

    Any Idea ??
    Thanks, Achim

  2. #2
    Captain Anmer's Avatar
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    What speed are you observing in your RV6? Ground or airspeed?
    Mike


    www.radarspotting.com

    Radarspotting since 2005

  3. #3
    Passenger fl95's Avatar
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    Both speeds. One from Pitot, one from GPS. Groundspeed goes from GPS to TRansponder ADS-B out, but not 550 knots
    Achim

  4. #4
    Captain
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    Could either be the transponder or the data input/transfer to the transponder.

    Problem on flightaware is the same, so it's not an FR24 problem.

    Maybe check the cabling, proper grounding and good voltage.
    Especially with the problem being intermittent that would be the first thing to check for me.
    (not a mechanic though )

  5. #5
    First officer
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    Dec 2014
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    I've just looked at two of your flights, the second one to make sure it wasn't possibly the same ground station reporting in error. Both have very erratic groundspeeds as you have already said. I have also looked at history tracks of some of my local aircraft and their groundspeeds are quite erratic too. Perhaps its a problem with breaks in coverage or the recording process, but I would not worry that it is anything to do with your ADS-B installation.

    I am assuming your GPS display is showing correctly and you haven't had any ATC reports that your transponder is failing.

  6. #6
    Passenger fl95's Avatar
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    Yes, GPS shows the correct Groundspeed also in its own logfile. ATC has no Problem with my Transponder Signals.
    Achim

  7. #7
    First officer
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    Quote Originally Posted by fl95 View Post
    Yes, GPS shows the correct Groundspeed also in its own logfile. ATC has no Problem with my Transponder Signals.
    Achim
    I've also had a look at your flight on the 22nd on the Planefinder site. On the leg tracking NW towards Bremen your speed at 4000' is 137 and down at 3000' it drops to 124. those speeds are very steady, not spikes at all, so its definitely the tracking sites/data that is the problem.
    Alles ist in Ordnung!

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