Flight Details
United Air Lines Flight 718 was a scheduled flight from Los Angeles to Chicago. The aircraft departed Los Angeles International Airport at 0904 from runway 25L, three minutes after TWA Flight 2. The flight plan specified an IFR route via Green Airway 5, with a cruising altitude of 21,000 feet and an airspeed of 288 knots. The crew consisted of Captain Robert F. Shirley, First Officer Robert W. Harms, Flight Engineer Gerard Flore, and Stewardesses Nancy L. Kemnitz and Margaret A. Shoudt. The aircraft carried 3,850 gallons of fuel and had a takeoff gross weight of 105,835 pounds, within limits.
Departure and Route
After takeoff, the flight was vectored by Los Angeles tower radar through the overcast on the same departure course as TWA 2. United 718 reported reaching "on top" and switched to Los Angeles Center frequency for en route clearance. The controller specified that the climb to assigned altitude be conducted in visual flight rule conditions. The flight made position reports via company radio, reporting over Riverside and later over Palm Springs intersection while still climbing to 21,000 feet.
Position Reports
At 0958, United 718 reported to the CAA communications station at Needles that it was over Needles at 21,000 feet, estimating Painted Desert at 1031 and Durango next. At approximately 1031, an unidentified radio transmission was heard by Aeronautical Radio communicators. Later analysis of the recorded transmission revealed it was from United 718, stating: "Salt Lake, United 718 . . . ah . . . we're going in."
Collision
The collision occurred at approximately 1031 in visual flight rule weather conditions at about 21,000 feet. The location was a short distance west of the TWA wreckage area, 17 miles west of the Painted Desert line of position. At impact, the two aircraft converged at an angle of about 25 degrees, with the DC-7 to the right of the L-1049. The DC-7 was rolled about 20 degrees right wing down and pitched about 10 degrees nose down relative to the L-1049. No evidence of mechanical malfunction or failure was found.
Probable Cause
The investigating board determined that the probable cause of the mid-air collision was that the pilots did not see each other in time to avoid the collision. It was not possible to determine why the pilots did not see each other, but evidence suggested it resulted from one or a combination of factors, including intervening clouds, cockpit visibility limitations, preoccupation with cockpit duties or other matters such as providing passengers a scenic view of the Grand Canyon, physiological limits of human vision, or insufficiency of en route air traffic advisory information due to inadequate facilities and personnel in air traffic control.