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As a result of restrictions necessitated by military activities in areas adjacent to the airway, the Civil Aeronautics Administration, on July 15, 1941, directed a written notice to TWA, as well as to other carriers, advising them that it was necessary to confine all operations between Palmdale, California, and Las Vegas, Nevada, strictly to the airway, and suggesting that pilots be instructed to confine their flight movements, day or night, contact or instrument, to the actual on-course signal of the radio ranges serving the airway involved. A communication directed to TWA flight personnel by TWA's acting chief pilot, dated July 17, 1941, incorporated this notice verbatim and requested pilots be guided accordingly. Copies were posted on pilot bulletin boards at Kansas City, Albuquerque, Burbank, and San Francisco.
The highest terrain along the correct course between Las Vegas and Silver Lake appears to be at an elevation of less than 6000 feet. The highest point within 15 miles on either side of the course line is Potosi Mountain, which, as previously indicated, rises to an elevation of approximately 8500 feet, and, while it is located on the airway, it is off the on-course signal.
There was received in evidence at the hearing a TWA flight log sheet form covering the route from Albuquerque to Burbank, via Winslow, Arizona, Boulder City, Nevada, and Newhall, California. This flight log sheet is a part of the pilot's navigation kit, and indicates proper courses for the various sectors of the route. It also contains a profile chart of the highest terrain along the course line and, in addition, the highest terrain within a strip, 30 miles in width, which extends 15 miles on either side of the course line. The highest terrain indicated for the course line between Boulder City and Silver Lake is approximately 5800 feet, and the highest point indicated within the 30-mile strip for this section is 9000 feet. The route between Las Vegas and Silver Lake is also shown on the log sheet,
