The pilot submitted a flight plan for a NOSAR flight to Paraburdoo indicating a time interval of 75 minutes and an ETD of 1630 hours WST. The time of last light at Paraburdoo was 1800 hours WST. The aircraft did not depart until 1711 hours and at 1733 hours, in a response to a query from Port Hedland flight service unit reminding the pilot of last light considerations, the pilot advised that he would divert to Wittenoom. Subsequent calculations indicate that it would not have been possible for the aircraft to have arrived at Wittenoom before last light. Effective VHF radio communications with the aircraft were then lost and the pilot has stated that his HF radio transmitter did not operate. The pilot became unsure of his position and in the failing light he decided to make a precautionary landing on a flat area covered in what appeared to be low bushes but which were, in fact, rocks. After touching down the aircraft struck rocks and subsequently overturned. Following an air search the aircraft was located at 0810 hours on 10th June, 1971 and the occupants were then rescued.