All present airspace in which it is proposed to have VFR aircraft fitted with the subsidised ADS-B has an existing requirement for all VFR aircraft to be fitted with a transponder and all airline aircraft to be fitted with TCAS (Traffic Collision Avoidance System). This means there is a highly proven, extraordinarily safe system at present. This not only gives traffic information on the VFR aircraft to the airline aircraft, with a visual display, but more importantly gives a verbal “Resolution Advisory” to advise the airline pilot whether to climb or descend to avoid a collision.

This is the airspace where Airservices are proposing to spend over $100 million in subsidising ADS-B fitment to small aircraft. The only change in practice will be that the ADS-B signal on the VFR aircraft will be transmitted to the air traffic control centre and appear on the air traffic controller’s screen. The same TCAS readings will still appear on the airline aircraft’s display if aircraft get too close together.

With the identification of the myriad of small aircraft appearing on the controller’s screen it will obviously create lots of extra jobs, but what actually will the controller do with all this information? Can anyone work out the extra safety provided by the $100 million?

The air traffic controller’s screen will normally show many dozens of airports with many aircraft apparently being close together. If there is an automated system in the air traffic control centre it will be constantly giving alarms and air traffic controllers will be constantly informing airline aircraft of the traffic that they already know of - having already communicated on the CTAF or seen the aircraft on the TCAS.

I believe there would be no measurable increase in safety for the extra $100 million. There could even be a decrease in safety because the ADS-B proposed for VFR aircraft is very much a one-off design that has not been through the incredible teething troubles and development process of the existing transponder/TCAS system.

Remember that TCAS has been around for over a decade and is now so reliable and so accurate that airline pilots must follow the TCAS “Resolution Advisory” even if it conflicts with an air traffic control instruction.

Could it be that the ADS-B proposal at Airservices is being driven by a “1950s culture” of bringing all the small VFR aircraft back into the air traffic control system as they were before 1991?

Why Airservices would want to do this is strange. It will most likely mean more ATCs will have to be employed - with an increased workload – and the legal liability will also be increased. However there is very little they can do for collision protection in the terminal area when the air traffic control sector covers a large amount of airspace.

There is little doubt that if it is economic for Airservices to remove the enroute radars, they can go ahead and do this and require IFR aircraft to have ADS-B and save the $100 million by not fitting “free” units to VFR aircraft. If these VFR aircraft still keep their presently mandatory Mode C transponders we end up with a very safe system with a substantial saving for the industry.

It has been pointed out to me that the $100 million that was planned by Airservices to be spent on fitting "free" ADS-B units to VFR aircraft was a saving that Airservices would obtain by not replacing the secondary surveillance radars. I fully understand this. What I am actually stating is that it would be better for Australian aviation if the $100 million was saved and given as a reduction in Airservices costs to the industry.

For example, the reduction in costs could be used by aircraft owners to purchase Enhanced Ground Proximity Warning Systems. Then we would really start saving some lives. It is well known that most fatalities in commercial aircraft are caused by controlled flight into terrain, not by mid-air collisions. Why would you want to spend $100 million (or not save $100 million) by allocating resources where the risk is almost immeasurably small (that is, a mid-air collision away from the aerodrome area) when you could spend that money on Enhanced Ground Proximity Warning Systems that would really save some lives?

Alternatively, the $100 million could fund 10 Class D control towers - by investing the $100 million and using the $5 million interest to run 10 Class D towers at $500,000 each. Or it could be used to run 100 UNICOMS with trained operators at $50,000 per year each. Then you would really be doing something worthwhile for safety. Commonsense and scientific analysis shows that the mid-air collisions are going to happen close to the runway. That is where a Class D tower or a trained UNICOM operator will have the greatest chance of reducing accidents. In fact, many collisions happen on the runway. Both a UNICOM and a Class D tower reduce the chance of a runway collision.

I'm not negative about ADS-B, I just don't want to see resources misallocated. Most importantly, to actually transmit a signal from an aircraft which not only identifies the location, but also the identification of the aircraft, is fraught with problems. What we need is a bit more design on the system so there is no way of identifying a particular aircraft.  I'm sure many will agree.

Entry last amended 13/9/05.