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SE2 traffic warning false alerts


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Tony N
Tony N
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Last week I flew to Sandown, IOW, on the last day before UK Lockdown No. 2.
The circuit was very busy due to airfield operational issues so I had to fly three circuits before landing.
I didn't do "touch and go" - I just continued to fly at circuit height.
Each time I overflew the airfield I received a warning about an aircraft at 35000ft above, overtaking at 330 Kt.
I think this warning occurred three times.
I didn't see anything on the moving map but wasn't really looking for long either due a fairly busy circuit.
I think SD was detecting high level CAT in the airway above me, so likely a glitch in the SD traffic filtering algorithm.
I have never detected anything similar at any other time and just use the standard default for a height filter in the basic SD setup.
Tony

Tim Dawson
Tim Dawson
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Interesting. I can only imagine the traffic way above was giving a false vertical speed, at least that's the only thing I can think of. It's not clear what we could do about this, since if that vertical speed were true, you'd probably want to be warned.
Tony N
Tony N
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Tim,

I looked at my flight with FlightRadar 24 and it was a Ryanair at FL380 that flew right over the top of me while I was in the circuit.
I can e-mail you a screenshot of the FR24 tracking if you like.
Tony

Tim Dawson
Tim Dawson
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No thanks, I don't think there's any particularly useful information it could give us.
Tony N
Tony N
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Tim,

Just to let you know I am still receiving the occasional audio warning of aircraft thousands of feet above me.
Last Friday it was an aircraft around 7000ft above and overtaking me at 330Kt.

I don't fly a high performance aircraft and was flying S&L.
My SE2 was the ADS-B In receiver.
Thanks
Tony

Tim Dawson
Tim Dawson
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Presumably because that aircraft briefly indicated it was descending towards you.
Tony N
Tony N
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Maybe, but I don't think so. Also I was at least 5000ft below the other aircraft.
Why would I want to hear a audio warning under that situation?
Or is the speed of the other aircraft causing SD's algorithm to get confused?

Tim Dawson
Tim Dawson
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SkyDemon isn't getting confused. Perhaps I haven't explained that very well in this thread; if so I apologise. If SkyDemon is giving you a warning, it's because some traffic has indicated it's on course to conflict with you. Period.

Perhaps its GPS system, or yours, gave spurious readings for a few seconds. Perhaps it actually did hit a pocket of air and begin descending very rapidly, also with high forward speed, to briefly put it on a collision course with you. I don't know, I can only speculate. Your posts here suggest that SkyDemon is doing something wrong, though, when I suspect it isn't.

Tony N
Tony N
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Thanks Tim,
I wasn't suggesting that SD was necessarily getting it wrong but also I wasn't sure why I would be getting these audio warnings from airliners many thousands of feet above me.

One thing I have noticed though, when viewing a flight via the SD logs feature, and "replaying" my flight, is the virtual radar display has quite a few "red dots" displayed.

The SD manual says this indicates a loss of GPS data but I have never seen any SD warning of this when actually flying.
My SD/SE2 combo seems to be working perfectly in the air.

Could this issue be related to SE2 - SD WIFI comms?
What is SD looking for to indicate that GPS data has been lost?
Is it checking every few seconds that data is being received, or similar?

I don't recall seeing the "red dots" last year when I wasn't using SE2 as my GPS source.
Tony

Tim Dawson
Tim Dawson
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GPS isn't all or nothing. The red dots in your virtual radar, assuming there are no red dots on the main map representation of your flight, mean that only altitude was lost and not the rest of the GPS information. It's not that unusual actually, though it does depend on what GPS receiver you're using. I am not an expert on GPS receivers by any means but the SkyEcho GPS receiver is certified, and altitude is the most fragile bit of the GPS data because of the geometry of the satellites, so it would not surprise me to learn that altitude drops out MUCH more often than the lateral position/track/speed data when signal isn't very good.
GO

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