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 Post subject: Incorrect ADS-B Position Reports
PostPosted: Fri Mar 17, 2017 4:22 pm 
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HuffTheWeevil - FlightAware user avatar

Joined: Tue Jan 06, 2015 1:25 am
Posts: 28
Can anyone explain what causes this:

Image

Clearly this UPS aircraft did not land on top of the terminals. It did indeed land on the runway a couple hundred feet to the south of that path. And once on the ground, it continued to report a position that was offset a bit and was a bit "sketchy". The real taxiway he exited on is actually off that image to the right.

This happens to about 0.5-1% of the flights I see.

And it's not MLAT (in my config, the lat/lon in the selected box would be italicized if this were an MLAT position).


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 Post subject: Re: Incorrect ADS-B Position Reports
PostPosted: Fri Mar 17, 2017 4:59 pm 
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FlightAware Staff
obj - FlightAware user avatar

Joined: Tue Sep 30, 2014 7:14 pm
Posts: 3322
Semi-constant position offsets like this usually mean that the ADS-B position reported is being derived from an inertial system (which drifts over time) not GPS


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 Post subject: Re: Incorrect ADS-B Position Reports
PostPosted: Fri Mar 17, 2017 5:10 pm 
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HuffTheWeevil - FlightAware user avatar

Joined: Tue Jan 06, 2015 1:25 am
Posts: 28
That was my guess. But I don't understand why an ADS-B unit would be set to rely on an IRS over GPS. I thought in today's world IRS was the backup.


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 Post subject: Re: Incorrect ADS-B Position Reports
PostPosted: Sat Mar 18, 2017 12:19 pm 
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NeoDuder - FlightAware user avatar

Joined: Sat Nov 26, 2016 11:17 am
Posts: 25
Location: EGPH
There's probably a switch somewhere to switch between the two but as ADS-B isn't really used much it probably doesn't matter where it is set.


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