An investigation led by the Civil Aeronautics Board (CAB) concluded that the pilot had made errors during the flight while trying to remain below the low cloud cover.
The flight crew may have experienced sensory illusions while flying in the darkness with only the distant lights of the airport ahead to use as a visual reference.
[1]: 1, 4 The weather was overcast at the time, with reported cloud ceilings at 800 feet (240 m) and visibility of ten miles (16 km).
This clearance had been available since April 1952 for traffic between San Francisco and Oakland and was used when cloud ceilings were below 1,000 feet (300 m) or when visibility was low.
As it completed the turn and flew over the San Francisco Bay, it was picked up on a primary surveillance radar system in operation at Oakland.
[6][3] After seeing the flash of light and the loss of the radar signal, the radar operator at Oakland made a note of the distance and bearing of the last position of the aircraft and called the Alameda Naval Air Station and the San Francisco Coast Guard Station to let them know that a plane had gone down in the bay.
[1]: 4 The water was littered with small pieces of wreckage, seat cushions, other debris, as well as a large oil slick that had burned for a short time after the crash.
[8] The survivors had been in the cold water for about an hour, holding on to foam rubber seat cushions to stay afloat.
[6] Tidal forces were causing the water currents in the bay to flow out to the Pacific Ocean, and by the middle of the next day there was no debris or even remnants of an oil slick to indicate the location of the accident.
[12] Designed with a capacity of 66 passengers, the airline's DC-6 fleet was placed in service on its west coast routes between Los Angeles, San Francisco, Portland, and Seattle in early 1953.
He had been employed by Western Air Lines since April 1940, and had a total logged flying time of 11,500 hours.
[4] He had flown for Western Air Lines since September 1946, and had total logged flight experience of 3,100 hours, of which about 38 had been on the DC-6B.
[4] The day after the crash, Coast Guard boats started their search for the main wreckage of the aircraft in the bay between San Francisco and Oakland.
[6][7] The CAB requested and received the assistance of a submarine chaser to start conducting sonar surveys over a six-square-mile (sixteen-square-kilometer) section of the bay, which revealed two locations with large objects on the bottom, suggesting that the plane had broken in half.
The largest portion that was recovered was the wing center section that still had the two main landing gears attached to it.
[17] During the hearings, one of the survivors, a flight attendant, testified that as the aircraft left Los Angeles, she heard a sound that seemed to her like a cable striking the outer cabin door.
[15] In San Francisco, the flight engineer and a mechanic from Western Air Lines performed a walk-around inspection of the aircraft, but they did not report finding any problems.
[15] Another survivor, a male passenger, testified that the flight seemed normal, and that the plane was flying below the clouds the whole time.
[15][1]: 5 He said the plane did not make any sudden turns or abnormal maneuvers before the crash, and that the wings were level when it hit the water.
Crews of other flights that were flying the Trans-Bay procedure in the hour before and after the crash reported cloud ceilings ranging from 400 to 1,000 feet (120 to 300 m).
The board members announced that they planned to study the result of the hearings and other investigations before releasing a final report.
The report concluded the probable cause of the crash was the pilot's controlled descent below the 500-foot (150 m) minimum altitude until the plane struck the water.