A Kawasaki BK117 helicopter, registered VH-CSG (CSG), departed Townsville on a flight to Cairns, Queensland, under the visual flight rules (VFR). The pilot requested a clearance from Townsville (military) air traffic control (ATC) to track outbound via the Rollingstone VFR route at 1,000 ft.  

At about the same time, a West Wing Aviation Cessna 404 aircraft, registered VH‑XDA (XDA), was inbound to Townsville from Palm Island, under the instrument flight rules (IFR). The aircraft was cleared by ATC to enter the Townsville military controlled airspace via the Rollingstone VFR route, at 1,500 ft, visual. This provided the required 500 ft vertical separation with CSG.

At 1502, the Townsville Approach controller (trainee) advised the pilot of CSG that he was now outside Class C airspace; provided traffic information on a military helicopter operating in the vicinity, about 10 NM ahead, on descent to 2,500 ft (operating in Class C); and that the Brisbane Centre frequency was available when 36 NM from Townsville. The pilot acknowledged the call.

As the pilot of CSG was aware of another aircraft operating in the area at 2,500 ft, the pilot elected to commence a slow climb to 1,500 ft, to maintain separation with the known traffic. 

At 1506:20, Department of Defence (Defence) radar surveillance data showed that CSG was at 1,400 ft and XDA was at 1,500 ft, with 0.1 NM lateral separation. At that time, the pilot of CSG observed an aircraft ahead (XDA) and immediately descended. The pilot of CSG reported that he was at 1,260-1,280 ft when he passed an estimated 20‑30 ft below XDA. 

The pilot of XDA was in the process of broadcasting an inbound call on the company frequency when he observed a ‘flash’ (CSG) an estimated 6 ft below. The pilot immediately initiated a climb. 

A Defence investigation determined that the Townsville Approach trainee, Training Commander, and Approach Supervisor were prioritising the provision of air traffic services to aircraft operating in Class C over the provision of a flight information service (FIS) to aircraft operating in Class G. While this led to compromised safety between XDA and CSG, this was not evident to the controllers as the prioritisation of tasks in Class C reduced their situational awareness of the developing situation in Class G. 

As a result of this occurrence, Defence has advised the ATSB that controllers have been briefed on the importance of providing accurate traffic information to IFR aircraft operating in Class G, and a training package has been incorporated into the Approach controller training guide to further develop controller understanding of the provision and importance of a FIS.


Aviation Short investigation Bulletin Issue 21