At 1529 EST 4 January 1993, the Brisbane Flight Service Centre monitored a Mayday call from an aircraft in the area of Jumpinpin on North Stradbroke Island. The caller was difficult to understand but indicated that he was having problems with the elevator control, that the aircraft was going down and he was switching everything off. The call sign of the aircraft was not determined. A search was commenced immediately and about 30 minutes later the wreckage of VH-JUJ was sighted lying inverted in a swamp on North Stradbroke Island. An inspection of the accident site revealed that after the landing gear contacted the ground the aircraft nosed over and came to rest inverted. Examination of the wreckage found no evidence of any pre-existing fault with the aircraft or its systems which may have contributed to the accident. The elevator was found to be trimmed nose down, half way between the neutral and full down positions. The magnetos were in the off position, the battery and alternator switches were on and the wing flaps were selected to, and in the up position. The pilot last completed a flight check in the aircraft type three weeks prior to the accident. The purpose of this flight was reported to have been to conduct practice forced landings. The pilot last completed a medical examination on 9 September 1991 and the medical records gave no indication of any illness being identified at that time. However, the specialist medical evidence obtained during the investigation showed that the pilot was suffering from an advanced terminal illness at the time of the accident. Medical advice suggested that one of the effects of this illness may have been that the pilot could at times experience a degree of confusion and/or physical impairment. The injuries received by the pilot in the accident were of a minor nature. However, he subsequently died in hospital of complications resulting from the terminal illness. It is likely that the health of the pilot was a significant factor in the development of the accident. While no evidence of a mechanical defect or obstruction with the elevator control, as reported by the pilot, was found, the elevator was trimmed considerably nose down. This would have the effect of making the elevator control feel heavier than usual. However, it would normally be expected that a pilot of similar experience would have quickly identified and corrected this situation. The indication that he did not suggests some degree of confusion/impairment on his part. SIGNIFICANT FACTORS: It is likely that the pilot suffered some form of incapacitation during the flight as a result of his medical condition.