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Voice communications received from the crew prior to the crash were made in a normal manner and at no time did personnel receiving them suspect concern or excitement. The last transmission, "Southeast, turning inbound," was made less than three minutes prior to the crash.
Investigation disclosed that BCPA flights were approved by CAA and by company procedures to make three types of instrument approaches to San Francisco: one radio range approach and two ADF approaches. The standard ADF approach from the southwest is over the southwest leg of the San Francisco low frequency radio range station to the range station at a minimum altitude of 3,000 feet, then outbound on the southeast leg at a minimum altitude of 2,000 feet followed by a left descending turn after passing the Belmont Fan Marker, then crossing the ILS outer marker inbound at 1,660 feet. The compass locators of the outer and middle markers are used in the latter part of the approach. The other ADF approach permitted a direct course from the Half Moon Bay Fan Marker to the ILS outer marker, a distance of 13.8 statute miles and at a minimum altitude of 3,500 feet. BCPA flight crews were not trained to make an ILS approach but when such approach was given they would accept it and use one of the ADF procedures. This latter was approved by CAA.
Company records disclosed during the investigation that both pilots had made more than 100 approaches to the San Francisco Airport, many of which were actual instrument approaches. Their training was adequate and in accordance with company requirements and the standards of the Australian Government.
In the course of the investigation, many ground witnesses were interviewed and written statements taken from seven. These persons not only pointed out significant factors concerning the accident but were generally in agreement on them. All agreed the crash site and surrounding terrain were covered by a dense fog and the aircraft could not be seen in flight. Also the aircraft, when heard, was flying very low with the engines sounding normal. One witness, located one and one-half miles south of Half Moon Bay near the coast, stated that from sound the aircraft seemed south of his position, flying from west to east, and that he heard it crash between one and two minutes after it passed his position. Witnesses who were cognizant of the time and who heard the crash were able to establish the accident as having occurred between 0842 and 0845. Also, witnesses near the crash site substantiated that the course of the aircraft immediately prior to impact was northeast, and that the impact was accompanied by at least one large explosion.
Weather conditions existing at the time of the accident were caused by a weak surface low pressure trough extending from Sacramento and the Bay area south-southeast to Monterey Bay with a high pressure area off the coast. This pressure gradient caused a stratus overcase with its base approximately 1,200 feet and its top about 2,500 feet. This condition also extended westward over the Pacific Ocean for several hundred miles, with varying degrees of cloud coverage. The freezing level was 12,000 feet. The fog and stratus overcast were clearing inland toward the coast and within a short time after the accident, clearing conditions existed at the San Francisco Airport. Good visibility prevailed both above and below the overcast in the instrument approach area and at the airport itself. The mountains to the west and the crash area at an altitude of 1,950 feet were covered by dense fog completely obscuring the terrain
