Originally Posted by
OCTA Aus
Your assumption isn't correct. The ADSB coverage in FR24 isn't representative of the ADSB coverage that ATC gets. Yes the STCA works in Class G airspace (the ATC system itself doesn't actually know what class of airspace the aircraft is in), however it has its limitations. The STCA has a 90 second look ahead, and its looking for if the aircraft getting to within 4.8NM of each other and 1000ft. It will only work if at least one of the aircraft is coupled up to a flight plan, and will only work if both aircraft are the same type of surveillance (ie ADSB/ADSB, or SSR/SSR, not one ADSB and one SSR). There are STCA inhibition areas around aerodromes, as aircraft are regularly operating very close there and we would constantly get false alerts. Most controllers try and keep an eye on IFR aircraft at an uncontrolled aerodrome and will give a safety alert if the aircraft look like they may collide, however when you are monitoring 1000 square miles of airspace with dozens of aerodromes you cant possibly be watching everything at once. Also operations in class G airspace tend to get very close to each other, so you get used to seeing aircraft in very close proximity.
That's very much for your reply.