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More detailed ADS-B data for N72EX?

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  • More detailed ADS-B data for N72EX?

    Would flightradar24 consider providing the complete set of ADS-B messages for the crash of N72EX on 26 January? I have been reconstructing the crash and having better GPS altitude and MODE-S data would really help. Here is a link to my work so far using the published fr24 data: https://www.youtube.com/watch?v=y66gKZ3oheo. Thanks for your consideration.

  • #2
    I made a granular data .KML for the last minute of flight. at two data frames per second, it's much better resolution. I have no idea how to render this to youtube. Would be interesting to see what you can do with it... made a .KML for the entire flight but there's more than 6000 records. It.s a cludgy beast. Google earth chokes for 4-5 minutes before it loads.

    attached. let me know if you need more .csv data...

    !!N72EXconvertcsv3.kml
    Attached Files
    Last edited by Patrick Reeves; 2020-02-05, 00:38.
    F-KDAG1

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    • #3
      Patrick, thanks for looking at this for me! What would really help me is a CSV file containing the following: Time, Lat, Long, Alt, GPS Alt, Track, Roll Angle, True Track Angle, Track Angle Rate, and heading (I know that is a tall order, and you might not log all of those values - or the helicopter might not have been emitting them).

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      • #4
        Here's what the header looks like:

        N72EXGranular.png



        You might be able to fudge the roll rate by comparing forward speed to amount of change in heading. I don't think ADS-B includes all those parameters you listed. Someone will
        Chime in if I'm wrong, though...
        F-KDAG1

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        • #5
          Thanks again for your investigations. In addition to the data you provided, the two parameters I would most like to see are roll angle and GPS altitude. I know that fr25 gets the GPS altitude because I can see it in live flights with my Gold subscription, but it is possible that you do not keep it historically. The roll angle is part of Mode S enhanced surveillance, and it possible that you don't get that data.

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          • #6
            Just to be clear, what would help me most at this point would be granular data for the last 30 seconds of flight containing: time, lat, long, alt, gps_alt, speed, track, vspeed, roll_angle. Thanks!

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            • #7
              I thought of one more data element that would help in each row: flightradar24 radar ID that collected the data. This is so I can resolve conflicting timestamps on each data point.

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              • #8
                (FYI- I have no connection with FR24 other than being just another feeder/user...)

                Feeder timestamps are synced to NTP to avoid timing errors. What sort of anomalies are you seeing?

                F-KDAG1

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                • #9
                  Looks like there was no geometric alt for this flight, last displayed receiving station was K-WJF1, near Lancaster in the high desert, but receiver is picked at random from many feeders receiving the same data-

                  Timestamps in the granular file are rounded to the nearest 1/1000th sec., as opposed to being rounded to the nearest whole second in the published KML file which will make the same second value appear in two consecutive records quite often, so no worries. It's accurate.


                  N72EXLastRecord.png
                  F-KDAG1

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                  • #10
                    Originally posted by Patrick Reeves View Post
                    (FYI- I have no connection with FR24 other than being just another feeder/user...)

                    Feeder timestamps are synced to NTP to avoid timing errors. What sort of anomalies are you seeing?
                    Sorry for the confusion, you are so knowledgeable I just assumed that you were with fr24! I am working with the high granularity dataset published by fr24 here: https://www.flightradar24.com/blog/k...icopter-crash/ .

                    Below are what I believe to be two identical ADS-B entries from granular data for the flight, but I suspect they were collected by two different receivers

                    Time hex callsign latitude longitude no_position altitude squawk speed track vspeed
                    2020-01-26 17:45:19Z.850 0xa9a1ad N72EX 34.13983 -118.70374 P 2100 1200 121 173 -1216
                    2020-01-26 17:45:20Z.840 0xa9a1ad N72EX 34.13983 -118.70374 P 2100 1200 121 173 -1216

                    The time difference in these messages is nearly a second.

                    I wonder why there is no Geometric data? There was earlier in the flight!

                    Playback.png

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                    • #11
                      So I just came across this blog post from fr24 https://www.flightradar24.com/blog/u...flightradar24/ It says "Reception of Extended Mode S data also requires that the air navigation service provider where the flight is operating is interrogating the aircraft’s transponder to request the data. While this is increasingly common, it is not yet universal." The GPS altitude stops updating about the time the helicopter got clearance to go into the San Fernando Valley. I am now guessing that they switched ATC and were no longer being interrogated for Extended Mode S.

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                      • #12
                        I have the same file, it does look like duplicate data. But wait. It gets weirder. the previous two longitude records are identical. And this occurs just as he maxes out his climb parabola and begins descending, in the middle of a sharp left hand turn, 23 degrees in less than a second. A lot of stuff going on. Maybe FR24 just couldn't keep up...

                        2020-01-26 17:45:18Z.300 0xa9a1ad N72EX 34.14099 -118.70384 P 2125 1200 112 196 320
                        2020-01-26 17:45:18Z.488 0xa9a1ad N72EX 34.14067 -118.70384 P 2125 1200 116 184 -320
                        2020-01-26 17:45:19Z.850 0xa9a1ad N72EX 34.13983 -118.70374 P 2100 1200 121 173 -1216
                        2020-01-26 17:45:20Z.840 0xa9a1ad N72EX 34.13983 -118.70374 P 2100 1200 121 173 -1216
                        F-KDAG1

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                        • #13
                          That's one of the reasons I want to see the flightradar24 "receiver code" so I can try to realign timestamps (if possible).

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