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Thread: Question related to BendixKing KT 74 Transponder versus FR24

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    Question related to BendixKing KT 74 Transponder versus FR24

    Hello,

    Hopefully this is the right place to put this.

    I have a brand new BendixKing KT 74 ADS-B transponder installed in my private aircraft.
    Everything works fine, ATC is happy and my aircraft can be seen in FR24.

    But occasionally FR24 is indicating 0 ft altitude for several minutes although I am at high altitude.
    - The transponder passed all tests with a transponder tester
    - The transpoder display is indicating correct altitude all the time during flights

    Do you know anything related to this problem with BendixKing KT 74 transponder and FR24?

    - mohair
    Last edited by mohair; 2014-04-06 at 18:01.

  2. #2
    Super Moderator speedbird1960's Avatar
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    Quote Originally Posted by mohair View Post
    Hello,

    Hopefully this is the right place to put this.

    I have a brand new BendixKing KT 74 ADS-B transponder installed in my private aircraft.
    Everything works fine, ATC is happy and my aircraft can be seen in FR24.

    But occasionally FR24 is indicating 0 ft altitude for several minutes although I am at high altitude.
    - The transponder passed all tests with a transponder tester
    - The transpoder display is indicating correct altitude all the time during flights

    Do you know anything related to this problem with BendixKing KT 74 transponder and FR24?

    - mohair
    What is your Mode-S code or Registration so Flightradar24 can check for the data.
    Last edited by speedbird1960; 2014-04-06 at 18:33.
    AMS Daily Fight Information: http://schiphol.dutchplanespotters.nl/

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    Quote Originally Posted by mohair View Post
    Hello,

    Hopefully this is the right place to put this.

    I have a brand new BendixKing KT 74 ADS-B transponder installed in my private aircraft.
    Everything works fine, ATC is happy and my aircraft can be seen in FR24.

    But occasionally FR24 is indicating 0 ft altitude for several minutes although I am at high altitude.
    - The transponder passed all tests with a transponder tester
    - The transpoder display is indicating correct altitude all the time during flights

    Do you know anything related to this problem with BendixKing KT 74 transponder and FR24?

    - mohair
    It is probably not you, you are probably passing over an area with poor reception and the feeder is only getting partial data, I don't know how the server handles this, but I would not be surprised if it just based your heading and speed on the last valid data to stop you dropping off the display altogether but does not do the same for altitude.
    Hopefully one of the admins can provide a fuller explanation.
    What happens if you make a turn or change speed while you are showing 0ft?
    FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

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    Quote Originally Posted by speedbird1960 View Post
    What is your Mode-S code or Registration so Flightradar24 can check for the data.
    My Mode-S code is A56206
    Ps. See also my post to update aircraft information in FR24 database.

  5. #5
    Super Moderator speedbird1960's Avatar
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    Quote Originally Posted by mohair View Post
    My Mode-S code is A56206
    Ps. See also my post to update aircraft information in FR24 database.
    I have just added your Aircraft to the Database, i will do some checks to see what i can find.

    Centre Map over Finland before you start Playback: http://www.flightradar24.com/data/ai...446mm/#30bf7f2
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    Quote Originally Posted by F-EGLF1 View Post
    It is probably not you, you are probably passing over an area with poor reception and the feeder is only getting partial data, I don't know how the server handles this, but I would not be surprised if it just based your heading and speed on the last valid data to stop you dropping off the display altogether but does not do the same for altitude.
    Hopefully one of the admins can provide a fuller explanation.
    What happens if you make a turn or change speed while you are showing 0ft?
    I don't think it is poor reception area. The position and the squak code is correct but the altitude is not right. This can happen in an area with several FR24 receivers at FL180.

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    Quote Originally Posted by speedbird1960 View Post
    I have just added your Aircraft to the Database, i will do some checks to see what i can find.

    Centre Map over Finland before you start Playback: http://www.flightradar24.com/data/ai...446mm/#30bf7f2
    speedbird1960,
    Thanks for the database update, it looks fine now!
    Last edited by mohair; 2014-04-06 at 19:30.

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    Super Moderator speedbird1960's Avatar
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    There does seem to be some sort of altitude error, on Playback dated 5/4/14/ when you where approaching Helsinki Malmi, your Aircraft was showing Altitude 11,200 ft / Vertical Speed +1920 fpm when should have been showing -1920 fpm as it was descending.

    Playback: http://www.flightradar24.com/2014-04...N446MM/30bf7f2

    Flightradar24 has good coverage in the Helsinki area, they have even got coverage on MLAT down to about 3500 feet.

    Looking at the data on the Map and taking into account other Aircraft near your Aircraft had no errors, i would say its possible your Aircraft has an intermittent Transponder fault, maybe keep an eye on future playbacks of your Aircraft to see if it happens again, you can then make a decision on whether you need to get it checked.

    Have a read of this article, as it explains about some altitude errors that can occur with Mode-S, its too technical for me to understand.
    http://flighttraining.aopa.org/magaz...ing_about.html
    Last edited by speedbird1960; 2014-04-06 at 20:15.
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    Quote Originally Posted by speedbird1960 View Post
    There does seem to be some sort of altitude error, on Playback dated 5/4/14/ when you where approaching Helsinki Malmi, your Aircraft was showing Altitude 11,200 ft / Vertical Speed +1920 fpm when should have been showing -1920 fpm as it was descending.

    Playback: http://www.flightradar24.com/2014-04...N446MM/30bf7f2
    Exactly. I have a friend (F-EFHK2) in FR24 community who has been looking received raw data and he is saying that only my aircraft is providing occasionally wrong altitude. That's why I am asking is this related only to my BendixKing KT 74 transponder?

    As an electronics engineer I think this can be related to the clock/timing margins of the FR24 receivers and the clock/timing of my KT 74 transponder asynchronous data.
    On the other hand ATC is happy with my KT 74 transponder.

    Are there are any FR24 hardware guys who could comment my findings?
    Last edited by mohair; 2014-04-06 at 20:12.

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    Hi all,

    I begin to get solid reception from N446MM on 5.4.2014 starting around FL100 and made some replay from stored AVR formatted datastream. During rest of the flight down to Malmi airport, altitude indications looks like to be correct without any strange anomalies. Also during that same part of flight when FR24 is displaying 0ft. I have had previously some interesting altitude error indications for this same plane, but these are related to one software tool which creates different kind user defined outputs from source stream AVR, Beast etc. etc. Altitude errors are only visible when using some specific outputs. So, some kind of software problem can be also reason for that.

    But anyway, interesting is that these errors are only seen when data is coming from N446MM. I haven't noticed that same phenomenon for any other commercial and general aviation flights inside my reception coverage area. That is something which is quite strange, I would personally expect similar errors to be displayed also for many other planes. I still have to try find out what would be the root cause for this one.

    Just to add... Looks like Virtual Radar Server (VRS) is providing proper altitude indications for N446MM, when VRS is connected to that Beast raw output.

    -----------
    F-EFHK2

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