@neilmurg @Tim Dawson
I agree with that principle. I have for a while now been involved in testing PilotAware Mode S-3D ‘positional’ signals, transmitted from my own Ground Station in West Edinburgh. Testing to collect specific data on positional accuracy is ongoing and now on a more scientific footing.
With few exceptions, the actual aircraft positions (from direct observation and comparison with other aircraft sites such as FR24) have complied fairly accurately with their indicated Mode S-3D positions, with the SD ambiguity circles generally indicating ‘time since last positional update’ rather than positional inaccuracy per se, - the position starting as a straightforward aircraft symbol with no ambiguity circle, then with a small circle appearing around it and expanding usually in 3 stages up to about +/- 1 NM then resetting back to a point as fresh position data is established.
Rather than reverting aircraft with NACp beyond this point to a Bearingless Target, I would suggest either keeping the initial (small) ambiguity circles and changing to a different ‘symbol’ to indicate any further reduction in ‘alleged’ reliability or replacing the ambiguity circles completely, with, for example colour, coded aircraft symbols to indicate the reliability (or otherwise) of positional accuracy.
It is important to remember that what we are trying to achieve here is to indicate position for the approximately 80% *
of GA (and other) aircraft in the UK who are still running pure Mode S Transponders and hence currently ‘Bearingless’, - i.e. with no known position
, so being able to show an accurate position of these aircraft with a small
degree of ‘uncertainty’ is surely significantly better
than what we have at present.
Remembering of course that the previous trials and ongoing testing indicate that the reported aircraft positions are highly accurate
in the vast majority of cases. * *
* Figure taken from a survey into EC device traffic levels obtained as a preamble to the ongoing CAA / FASVIG sponsored HIAL Dundee Trials.
* * Reference the NATS GA ADSB / GPS Trials Reporthttps://nats.aero/blog/wp-content/uploa ... report.pdf