The aircraft was being flown on an air test after a previous flight incurred a defect with the emergency gear extension system. The test was conducted in the Bankstown training area and all gear extensions both normal and emergency worked correctly. On return to Bankstown for landing on runway 29 Right the landing gear was lowered on downwind in the circuit and the normal three green indication was noted. The approach and landing was normal until just as the nosewheel touched the runway the right maingear collapsed and the aircraft skidded to a halt to the right of the centreline. Subsequent investigation revealed the right maingear jury strut pin had separated from the attach bracket on the rear spar. The strut pin retaining circlip had been incorrectly fitted during the last installation.