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Unexpected GPS data encountered


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ge89
g
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I struggle with the same problem. Since it's a rental plane, I can only report the problem to the flying club and hope they would contact the manufacturer (which they won't just because of a single complaint).

While I understand and support the policy of rejecting bad data, I wonder if there is not a better way to handle it in Skydemon. As already pointed out by others, ending the navigation mode and thus forcing the user to deal with a technical issue in flight is not optimal.

When losing connection to the traffic receiver a manual fallback mechanism is provided. Wouldn't it be possible to use a similar mechanism in case of bad data? SkyDemon shuts down the communication with the device, displays a banner indicating that bad data has been received and therefore no location/traffic information is available. By acknowledging the banner, SkyDemon stays in navigation mode and temporarily reverts to using the device’s Location Services (if available). SkyDemon reconnects to the traffic receiver in the background and as soon as valid data is received, SkyDemon will automatically switch back. When the user intentionally ends the navigation mode (e.g. after the flight), a complete error message can be displayed.

Finally, this would still follow the reasonable policy of rejecting bad data (not tolerating/ignoring corruption) and the user would be informed (multiple times) of a possibly erroneous behavior of the traffic receiver. At the same time, the user would not directly be burdened to deal with it in flight, can keep navigating, logging the flight and no timers would be reset.
Markus
Markus
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Yes, it is/was in German airspace, in this case south-east of Frankfurt.
How could I tell, if it was a windmill?
Edited 4/19/2022 2:59:55 PM by Markus
BJS
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markus - 3/28/2022 10:05:32 AM
If it helps, I had the same error last Saturday for the first time. (but 2-3 times in a row)
(Until then, I've never seen that bug in 2+ years)


Let me guess, you are flying in German airspace? Did you check whether this is a windmill obstacle? There is increasing trouble with windmills and other stations getting equipped with non-standard transmitter.

Edited 3/28/2022 11:56:16 AM by BJS
Markus
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If it helps, I had the same error last Saturday for the first time. (but 2-3 times in a row)
(Until then, I've never seen that bug in 2+ years)


Tim Dawson
Tim Dawson
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Thanks Florian, that's really helpful. Just testing with the first sentence it's obvious that your device is sending very bad data. The checksum is correct, which means the data was NOT corrupted in transit (SkyDemon would have ignored it in that case).
$PFLAA,0,-14084,-259068,-10144,4187,1,3C60D4,129,,209,10.0,8*55
The sixth field in that sentence has a value of 4187. That field is called IDType, and is supposed to have a value from 0 to 3.
We are correct to not only reject that data, but to do so forcefully. A device outputting such bad data has obviously got itself into a very poor state and goodness knows what other bad data it will be putting out.

Peer
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Florian,
thank you very much for your investigations.
Hope you and SD will find the bug.
Peer



Florian Meissner
Florian Meissner
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Hi Tim,

so far I could not any tests in. The weather was to bad to get enough other FLARM traffic airborne.

Anyway, I worked through the screenshots I took over the ast few month in order to find anomalies within the data. In the attached spread sheet (Libre Office) you can find different sentences which were rejected by SD. They are pares into the spreadsheet like the CSV import would do (fields would be comma separated).

The column headers are the data structure from FLARM's latest data port interface control document(FTD-012, V7.10). I used current firmware for the TRX-1500and FLARM and the latest SD-Version in Google Play for all tests. So I assume that the FTD-012 document applies to the TRX-1500, too, since it is essentially a PowerFLARM working within.

What I see at first glace is that first, all of the PFLAA targets are quite far away. Also in all sentences the amount of fields does not correspond to the specification and that the order of the fields seems to be messed up.

Anyway, the checksums are still valid.

With better weather approaching I will continue to find out, who messes up the data. The FLARM inside the TRX-1500, the TRX itself, the AirConnect or SD.

Another approach I will try is to drastically limit FLARM's range since all invalid targets seem to be far away and so all seem to be ADSB-Out targets. Thinking of the weather and the amount of GA traffic at these times, I even suspect, these were IFR airlines.

I will let you know, if I find out more.

Florian

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messed_up_sentences.xls (568 views, 10.00 KB)
screenshots.zip (586 views, 1.00 MB)
Florian Meissner
Florian Meissner
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Hi Tim,

let me see, what I can produce next weekend when I am out flying. I will try to document everything as thorough as I possibly can!

Florian

Tim Dawson
Tim Dawson
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I don't know which product is at fault. We have a TRX1500 and Airconnect in the office for testing, and we have never managed to reproduce the data errors you are seeing.

Certainly a log might be helpful, because we could then run that through our parsers to identify the nature of the corrupt data.

Florian Meissner
Florian Meissner
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Hi Tim,

ok, but how much do you know about the TRX.-1500 and Airconnect? The question now is, are the corrupt sentences produced by the TRX-1500 or is it the Airconnect messing them up?

Might it help if I connect my notebook into the WIFI and log the communication?


Florian

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