Analysis
The propeller difficulty reported shortly after takeoff from Honolulu probably had no bearing on this accident stance the trouble was reported by the flight to have been eliminated and no further reference was made to it in the numerous communications throughout the extensive flight.
The flight was conducted in accordance with an IFR clearance but was above clouds and the pilots apparently were not required to fly actual instruments for any appreciable length of time. The weather in the San Francisco area presented no adverse flight conditions such as turbulence or icing; however, visual reference with the ground was precluded by the overcast as far as is known, and an instrument approach was required.
As the flight neared the coast, it was given its approach clearance which was acknowledged and repeated back. This clearance required the flight to maintain at least 500 feet above all clouds from the Half Moon Bay Fan Marker to the ILS outer marker. The accident site was between these two points. It is obvious the flight did not maintain at least 500 on top and descended in weather conditions which precluded visual reference to the ground.
The flight reported over the Half Moon Bay Fan Marker at 0839 and then reported, "Southeast, turning inbound," at approximately 0842. The crash took place between 0842 and 0845. It seems impossible in this time interval for the flight to have flown from the Half Moon Bay Fan Marker to the ILS outer marker, made the required turn and returned to the crash state, assuming a normal speed. This is especially true considering that a part of the distance was flown with the landing gear down and 15 degrees of flaps extended. Thus it is likely that when the pilot reported "Southeast, turning inbound," his actual position was southwest of the airport. It is therefore probable that the captain after reporting over Half Moon Bay either saw the terrain momentarily through an unreported break in the overcast or because of a radio navigational error became convinced that his position was farther northeast, and started to let down over what he believed was the proper area for this descent.
Findings
On the basis of all available evidence, the Board finds that:
1. The carrier, the aircraft, and the crew were properly certificated according to appropriate regulations of the Australian Government.
2. The aircraft was loaded to a weight less than its maximum allowable and its center of gravity was located within prescribed limits.
3. Propeller relay difficulty was eliminated shortly after takeoff and the flight from Honolulu to the Half Moon Bay Fan Marker was otherwise uneventful.
4. The clearance griven the flight for its instrument approach to San Francisco Airport was proper, was acknowledged, and was read back correctly.
5. The radio navigational and landing facilities for this area were functioning normally at the time the approach was being made.
