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Thread: Why those no-sense Air Temperatures?

  1. #1
    Join Date
    Mar 2017

    Why those no-sense Air Temperatures?

    Hi all
    Maybe you noticed this in the past but I constantly see fake Air Temperature readings when tracking Flights at only FL100 or inferior in my region (Canary islands).

    Those numbers (i.e. -67 ^C or +37 ^C) are clearly fake readings.
    So, what happens with the data that FR24 is managing?

    FR24-150517-0908UT.pngFR24-2017-05-15 0926UT.png

  2. #2
    Captain fungus's Avatar
    Join Date
    Mar 2010
    Sydney, Australia
    I've also noticed this occurring around here in Australia at low altitudes, particularly near an airport or on the ground with those aircraft which display these parameters.

    If you google 'ads-b and air temperature measurements' you'll find plenty of information relating to this. From what I'm reading these measurements are actually calculated within the aircraft, broadcast via ADS-B (transponder) and certainly not 'fake' on the part of FR24. They also go on to explain that they are used for measuring the air temperature and wind direction (as well as other parameters) at high altitude so I'd think the measurements at low altitude may be meaningless.

    Certainly an interesting topic none the less.

    The following article, whilst pretty technical, outlines how this data is derived and how it is transmitted (at least during a test phase in Australia) for both Mode-S and ADS-B equipped aircraft and also why the results may be erroneous at lower altitudes;

    Apparently an aircraft transponder can 'hold on' to older data if it doesn't receive an interrogation which would help to explain what we are seeing.

    Last edited by fungus; 2017-05-15 at 12:12. Reason: corrected spelling etc
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  3. #3
    Super Moderator
    Join Date
    May 2011
    T-NZCH1, PP:PH New Zealand
    Both are MLAT targets, so it's probably best guess on location from weather reports or legacy info as the data given is at a minimal as it is.

    Not to mention at 5000ft here one is indicating -69C

    Probably 3rd party supplied by weather predictions more than transmitted
    For instance at 18,000ft (500hpa) its -20ish,-43.794
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

  4. #4
    Join Date
    Mar 2017
    Thanks guys.
    Btw it also happens with non-MLAT traffic as you can see:

    And look at the wind speed too!
    It look like they display weather data typical of FL300-350 when the plane is flying indeed at ~1500ft

    Definitely there is some room for improvement here.
    Orange Pi PC Plus + NooElec NESDR SMArt + homemade 6 ele CoCo

  5. #5
    Team FR24 Mike's Avatar
    Join Date
    Feb 2010

    Limitations and Future Enhancements
    As Extended Mode S data is received directly from the aircraft it is subject to reporting error. The most common error in incorrect Mode S data is an unrealistic Mach value. Erroneous values in other data sets are also possible. We are also limited by the number of aircraft broadcasting Extended Mode S data. While the number of aircraft broadcasting full or partial Extended Mode S data is increasing, it is generally limited to aircraft with a newer transponder.

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