The pilot reported that there was no indication of a malfunction when the landing gear was retracted, after takeoff from Mt Isa. The flight was uneventful and the landing gear indications (three green) were normal when the gear was selected down, in the circuit at Birdsville. The gear indications were rechecked and confirmed again on final. Touchdown on the main landing gear was normal, but as the nose wheel tyre contacted the runway the nose landing gear collapsed. The aircraft then slid to a halt on the edge of the sealed runway left of the centreline. All four persons on board were able to exit the aircraft safely. The investigation found that the cage surrounding the rod end ball of the nose gear actuator rod had broken. This then allowed the actuator to disconnect from the drag brace assembley, which caused the nose landing gear to collapse, as the landing loads were applied. .