Originally Posted by
Centrex
ATC positioning was not that accurate some years ago in class G. On one IFR night flight, out of cloud east of Melbourne, we were told of traffic that was overtaking us on the port-side. All three pilots were fixated looking for traffic in that direction and after a minute or so, one of the pilots turned to check starboard where we saw an old twin with no strobes approx 400ft diagonally separated on the same heading. ATC was content with this until the PIC asked for greater vertical separation. We had just had a ADS-B/s installed when they were not mandatory and assume this other old twin did not. Does anyone know how accurate the system would have been if we both had newer transponders?
The reason the radar separation standard is 5NM is because it has to allow for the errors in the system. At a guess I would assume the SSR radars are accurate to within 2NM. Therefore at 5NM apart by radar you should still be 1NM apart even if both radar positions are at the extremes of their errors. So yes, I’m not surprised that an aircraft was on the opposite side to what the radar said. The raw RADAR feed that goes into Eurocat actually is quite a mess, it goes through many filters and radar processors before it goes onto the control display.
ADSB would likely be far more accurate, I believe it broadcasts position twice every second. However the position symbol in the control system will still only update once every 5 seconds.