On 17 January 2013, the flight instructor and student pilot of an Alpha Aviation R2160 aircraft, registered VH-NZT (NZT), had completed a training flight in the local training area to the west of Bankstown, New South Wales. They were returning to Bankstown via the ‘Prospect Reservoir’ (Prospect) visual flight rules (VFR) approach point, maintaining 1,500 ft.
At the same time, the instructor and student of a Diamond DA 40 aircraft, registered VH-UNH (UNH), were also returning to Bankstown via Prospect after conducting flying training in the local training area. They had been operating between 2,500 and 3,500 ft and elected to conduct a shallow descent to arrive at Prospect maintaining 1,500 ft.
When about 3.5 NM from Prospect, UNH passed overhead NZT with about 500 ft vertical separation. Shortly after, vertical separation reduced to 200 ft, with 0.2 NM lateral separation.
This incident highlights the importance of maintaining traffic clearance ahead and below, and for pilots to be mindful of aircraft blind spots.