Page:CAB Accident Report, Western Air Lines Flight 636.pdf/8

 Nevertheless, the Board is of the opinion that this operation requires special attention to insure that no relaxation of safety standards occurs in the conduct thereof, and further, the Board now has under active consideration the present regulation to determine whether any additional measures are required to insure an adequate margin of safety in trans-bay operations.

On the basis of all available evidence the Board finds that:


 * 1) The company, the aircraft and its crew were currently certificated.
 * 2) The flight was dispatched in accordance with the provisions of the Visual Trans-Bay clearance as outlined in the Joint Operations Letter - Revised effective April 10, 1952.
 * 3) The reported weather conditions at San Francisco and Oakland at the time of departure were above the prescribed minima.
 * 4) Actual weather conditions at San Francisco and Oakland at the time of departure were above the prescribed minima.
 * 5) Actual weather conditions over the Bay at the time and place of the accident were later determined to be below the prescribed minima for trans-bay clearance.
 * 6) The pilot of the aircraft failed to comply with the instructions provided in the Visual Trans-Bay procedures which are to be followed in case ceiling and/or visibility below prescribed minima are encountered en route.
 * 7) No evidence was found of mechanical malfunction of the aircraft or any of its components recovered.
 * 8) The flight descended below minimum specified altitude in an attempt to maintain visual reference.

The Board determines that the probable cause of this accident was the pilot's action in continuing descent below the 300-foot prescribed minimum altitude until the aircraft struck the water. A probable contributing factor to the aircraft striking the water was the sensory illusion experienced by the pilots.

BY THE CIVIL AERONAUTICS BOARD:

Joseph P. Adams, Member, did not participate in the adoption of this report.