As the aircraft turned on to base leg at Brisbane Airport, Australia, the landing gear and 25 degrees of flap down were called. The pilot-in-command inadvertently set the flap at 35 degrees and there was a brief discussion on the desirability of this setting. The first officer was satisfied to allow it to remain at 35 degrees until further flap was required but nevertheless the pilot-in-command re-set it at 25 degrees. The first officer then asked if “three greens” (indicating undercarriage down and locked) were visible and the pilot-in-command replied in the affirmative. The final approach was made with 14-15 inches of manifold pressure and 2250 rpm and full flap was lowered at the appropriate height. As the aircraft neared the runway the flare-out commenced and the first officer reduced power. Almost immediately the undercarriage warning horn sounded and the first officer commenced to re-apply power preparatory to climbing away. At the same time he asked if “three greens” were visible and received the reply from the pilot-in-command “yes three greens visible, go ahead and land”. The first officer, therefore, closed the throttles and, with the undercarriage warning horn sounding, placed the aircraft in a landing attitude. Immediately before touch down he realized that the undercarriage was not extended but at this stake it was too late to climb away. The aircraft slid to a standstill along the runway. The occupants were uninjured and quickly evacuated the aircraft. Conclusions: The investigators concluded that : (a) The cause of the accident was that the pilot-in command believing that he had lowered and checked the undercarriage, countermanded action by the first officer to carry out a baulked approach when the audible warning sounded during the final approach to land. (b) The reasons for the pilot-in-command’s erroneous conviction that the undercarriage was extended and locked throughout the final approach to the runway have not been determined. (c) The throttle setting for actuating the warning horn was set lower than normal but had no bearing on the accident as it sounded at a stage when the aircraft could have been easily and safely climbed away.