For the last stage of a flight from Perth to Adelaide, the pilot flight planned for flight from Ceduna to Parafield using night VMC procedures. The area forecasts indicated that the en route weather would include some areas of cloud at a height which would preclude flight at the minimum safe altitude defined by the night VMC requirements. Some rain showers and drizzle were also expected. The pilot nevertheless elected to depart Ceduna at 1805 hours CST for a flight via Cowell and Ardrossan, and encountered last light at approximately 1839 hours Radio communication was established with Ceduna and Adelaide but propagation conditions deteriorated and effective contact with the aircraft was not made after 1852 hours. Witnesses located in areas to the north west of Cleve saw the lights of, and heard an aircraft after 1910 hours. The aircraft was observed on various headings and, at 2025 hours the lights of the aircraft were seen, very low and heading towards the higher ground of the accident site where drizzling rain was falling. The impact of the aircraft with the ground was heard and local residents quickly located the wreckage. The aircraft had flown into the ground in essentially level flight just below the top of a sandy ridge some 950 feet above sea level.