VH-COG was cleared to take-off from runway 11, to make a left turn and depart not above 1000 feet. On initial climb the pilot was advised that VH-UDB was on mid right downwind for runway 36. The pilot of VH-UDB was also advised that VH-COG had departed from runway 11. The pilot of VH-COG scanned the downwind leg of runway 36 for VH-UDB without sighting it, and as VH-COG passed the entry point for the downwind leg of runway 36, while climbing through 800 feet, he assumed that VH-UDB would now be approaching right base and therefore well clear.
VH-UDB then passed directly over his right wingtip with a vertical separation of about 150 feet. The instructor and student in VH-UDB, who were also looking for VH-COG, saw it at the same time. As both aircraft were being operated in the VFR category, in accordance with MATS Chapter 4, Para 10, RAAF ATC were not obligated to provide separation in the CTR, and therefore not monitoring the progress of the two aircraft.
