John,
I don't know what failed. We use a combination of radar and ADSB these days, so I assume there would be reasonable coverage in the area.
For the non-pilots, to understand how the system works today, one needs to understand how it worked before it was interfered with...
The previous system had FS (Flight Service), who were not Air Traffic Controllers. They operated the non-controlled airspace beneath controlled airspace. They provided flight following, traffic information (essential) for all aircraft on a flight plan, and coordinated clearances with ATC for those aircraft entering controlled airspace from below. They also manned the now defunct briefing offices around the country, where we used to do our flight planning. Places like Dubbo also provided a traffic information service at the aerodrome as well
They provided a valuable, and IMO, an essential service.
Air Traffic Control just looked after controlled airspace via its enroute, approach, departures and tower controllers. They provided positive separation, either by radar or by procedural means (in the absence of radar coverage). Procedural separation involves the use of time, distance and altitude restrictions between aircraft based on reports from the pilots, and mathematical calculations by the controller. Kind of like a 3D game of chess, which had to be very accurate. Procedural separation is still used today at Class D towered airports, such as Coffs, Mackay, Rockhampton, Tamworth etc.
The same procedural model was used by Flight Service for assessing potential traffic to pass on to pilots for their own separation purposes.
Fast forward to today: With the closure of Flight Service in the early 90's, pilots operating outside controlled airspace now get a significantly lower priority and level of service. This is now provided entirely by an otherwise busy ATC, who looks after the overlying controlled airspace.
The limit of service is between IFR and IFR traffic (remember the ATC is looking after overlying airspace, too). VFR aircraft generally don't receive a service, and without ADSB/radar or actually speaking with ATC, ATC won't even know the VFR aircraft is there, so how can they provide a service?.
Theoretically, with thecurrent system, if both yesterday's aircraft were IFR, they should have received (at the very least) a traffic advisory service from ATC using discrete transponder codes. If there is ADSB/radar coverage in the area, ATC could tell them exactly where the other aircraft was. Nevertheless, both aircraft would have known about the other.
If one aircraft was VFR (and squawking code 2000), ATC would tell the IFR aircraft of "an unidentified VFR paint 3 miles north of Mangalore at 4000 feet unverified" (or similar). This is workload permitting for ATC (I think).
If both aircraft were VFR, ATC will only provide a service on request, and only if their workload is permitting. Remember, they are controlling aircraft in the airspace above.
In all of this, even if ATC provided a traffic information service to these guys yesterday, it's still up to the pilots to talk to each other and coordinate their own separation procedurally. If there was an imminent conflict, ATC would usually alert the pilots that they were at risk of collision, but the pilots would still need to take their own evasive action. We don't know about this aspect, yet.
Notwithstanding all the above, The pilots should have been talking to each other either on the CTAF, on the area frequency, or both to arrange their separation. We don't know (yet) whether they were. This is where the airspace limitations and human factors come into effect. Limitations of the system? There are many. Combined nearby airports on the same CTAF frequency, which are often jammed by aircraft operating many miles away, preventing timely broadcasts (the old analogy of 'can't get a word in edgeways'). To monitor both area and CTAF, you need 2 radios. Did they both have 2 radios? Was the ATC overloaded looking after all that airspace? These are but a few limitations.
Human factors is more complex, and a can of worms. Operating into a busy CTAF is one of the highest risk operations you can do. I'm not afraid to say I hate operating the jet into them. You typically have a lot of relatively inexperienced pilots operating there. Toss in a busy flying school or two, and it's even tougher. A lot of students who have very little experience dealing with large numbers of aircraft (it's not their fault). Developing a mental model of the traffic situation requires skill and experience that students may not have. There are many other scenarios that I won't bore you with...
I understand both flights were advanced training flights with highly experienced pilots onboard. That's a particularly difficult situation to be in - delivering your lesson effectively and maintaining an effective traffic picture in your head. I did that for many years, and it's as challenging (but in a different way) as taking the jet or high performance turboprop in.
I'll be interested to hear the outcome. I'm not surprised it happened. It's almost happened countless times before under the "new" system. It was only a matter of time, sadly...
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