I Was on the ground and listening to the CTAF frequency, A B1900 was in the circuit and made all the appropriate calls, there was also a c210 inbound from the north west at approx 4nm and going to join downwind for 35 as the 1900 was turning base for 17. No calls were made from the duchess until he replied 'sorry about that, was on the wrong frequency' when he was on short final. At this point both aircraft went around. Rumour has it the duchess was on some sort of flight test. Where was the instructor???? Probably from Bankstown???? Good luck on passing that one MATE!!!!