aircraft position when on deck

[mdobuk21]

hi guys

just tracked a tcx a320 into lba got him on the deck but when i zoom in on the airport the aircraft is way off the airport itself!! anyone know why?

cheers
mark

[Allocator]

Wrong position information transmitted by the aircraft.

Remember that ATC are not using the ADS-B position information for controlling aircraft, so there is no "policing" to make sure that correct position information is being sent.

[Keith L]

I noticed this on my awayday to Luton today.  What confuses me is that at home I see aircraft on the centreline down to about 200ft agl but visiting the airport today landing aircraft were consistently depicted as a couple of miles south of the airfield.  I was pretty much at the side of the runway (maybe 200yds) but landers all seemed to be heading in the opposite direction after landing, maybe too close and not high enough above the runway?

[Allocator]

Not quite sure what you mean about "heading in the opposite direction after landing"

Did you set your new home position in the RB Preferences while you were at the airport?

[Keith L]

Yes, set EGGW as new home location but landing aircraft were merrily tootling off towards the east a couple of miles south of the airport on RB when I was watching them with the naked eye continuing west then north to the stands.  I still suspect that the fact that I was on the same level and close to the runway caused this anomoly.

[Allocator]

I don't have any problems when I'm at Manchester Aviation Viewing park.

You say that you put EGGW in as the home location - I take it that you mean that you put the Lat and Lon for Luton into the Preferences > Home Station Data boxes.  Can you remember what lat/lon you used?

[Keith L]

N51.8745 W0.3683 I think.

[CoastGuardJon]

Hi Allocator and Keith, are you thinking along the same lines as me?   If the Home location is entered as one position, but the RB is actually located, say a mile east or west, the direction of the aircraft shown could be reversed to what it actually is - I've just used Multimap OS display and make the centre of the runway as map ref TL125207, which is 51.87379 and -0.36649.   When I first entered my Home location, the polar digram was very interesting Home was shown in eastern France - then I realised West of Greenwich position has to be entered as a minus quantity.

[Keith L]

Not sure Jon, I'm not sure I understand why the 'home' location should affect anything.  Suffice it to say the cross was in pretty much the right place on the screen.

[Allocator]

N51.8745 W0.3683 I think.

that looks OK, but it would have to be entered as

51.8745   -0.3683

Did you set the airfield QNH as transmitted by ATIS or ATC (if you didn't have a mobile Broadband connection)? Preferences > RadarBox.

If you did all this, then I don't know why you had odd positions.

I wonder if anybody else has operated from Luton?

[Allocator]

That

Not sure Jon, I'm not sure I understand why the 'home' location should affect anything.  Suffice it to say the cross was in pretty much the right place on the screen.

It depends on how RB displays positions.  Are they absolute, or are they relative to the Home position?  I think that the positions are absolute.

I remember the home position being critical when I was using the SBS-1.  I seem to remember that there were "grids" and if the home position was in one grid, but the actual location was in the next grid, you could get odd effects.

Did you make a RB Recording while you were at Luton?  It's good for reviewing traffic later and for investigations just like this one.

[Keith L]

Yes, Allocator that's how I entered the coordinates.  The QNH thing is interesting - I entered QFE to see if it showed 0 on landing (it did), I wonder if that is the problem?

[Keith L]

Unfortunately I didn't make a recording.  I thought I'd done a screenshot but apparently not.  Next time I can dodge the wife for a couple of hours I'll pop up and have another go complete with recording ;-}

[Keith L]

See http://www.airnavsystems.com/forum/index.php?topic=2154.msg17905#msg17905 for examples of anomolies within a couple of minutes of each other

[Allocator]

But this example shows different aircraft, so it's quite possible that one of them was sending incorrect position info.