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The 1956 Grand Canyon mid-air collision occurred on Saturday, June 30, 1956 at 10:30 am Pacific Standard Time when a United Airlines Douglas DC-7 struck a Trans World Airlines Lockheed L-1049 Super Constellation over the Grand Canyon within the boundaries of Grand Canyon National Park, resulting in the crash of both airliners. All 128 on board both flights perished. It was the first commercial airline crash to result in more than 100 deaths, and led to sweeping changes in the control of flights in the United States. The location of the crash has been designated a National Historic Landmark. ==Flight history== United Airlines Flight 718, a Douglas DC-7 Mainliner named ''Mainliner Vancouver'', and flown by Captain Robert Shirley, First Officer Robert Harms, and Flight Engineer Gerard Fiore, departed Los Angeles International Airport at 9:04 am PST with 53 passengers and five crew members aboard (including two flight attendants), bound for Chicago's Midway Airport. Climbing to an authorized altitude of 21,000 feet, Captain Shirley flew under instrument flight rules (IFR) in controlled airspace to a point〔The "Palm Springs" intersection was at about 33.92N 116.28W.〕 northeast of Palm Springs, California where he turned left toward a radio beacon near Needles, California, after which his flight plan was direct to Durango in southwestern Colorado.〔The report says their flight plan was Needles direct to Durango, but it's unclear what "Durango" means. There never was an LF/MF radio range there, and it seems the VOR wasn't there in 1956.〕 The DC-7, although still operating under IFR, was now "off airways"—that is, flying in uncontrolled airspace.〔CAB Docket 320, File 1, History of Flights, Section 2, issued 1957/04/17〕 Trans World Airlines Flight 2, a Lockheed L-1049 Super Constellation named ''Star of the Seine'', with Captain Jack Gandy, First Officer James Ritner, and Flight Engineer Forrest Breyfogle in the cockpit, departed Los Angeles at 9:01 am with 64 passengers (including 11 TWA off-duty employees on free tickets) and six crew members (including two flight attendants and an off-duty flight engineer), and headed to Kansas City Downtown Airport, 31 minutes behind schedule. Flight 2, initially flying IFR, ascended to an authorized altitude of 19,000 feet and stayed in controlled airspace as far as Daggett, California. At Daggett, Captain Gandy turned right to a heading of 059 degrees magnetic, toward the radio range near Trinidad, Colorado.〔CAB Docket 320, File 1, History of Flights, Section 1, issued 1957/04/17〕 The Constellation, like the DC-7, was now "off airways." Shortly after takeoff, TWA's Captain Gandy requested permission to ascend to 21,000 feet to avoid thunderheads that were forming in the vicinity of his flight path. As was the practice at the time, his request had to be relayed by a TWA dispatcher to air traffic control (ATC), as neither flight crew was in direct contact with ATC after departure. ATC denied the request; the two airliners would soon be reentering controlled airspace (the Red 15 airway running southeast from Las Vegas) and ATC had no means of providing the horizontal separation required between two aircraft at the same altitude. Captain Gandy requested "1,000 on top" clearance (flying 1,000 feet above the clouds), which is still IFR, not VFR (visual flight rules), and then was approved by ATC. The provision to operate 1000’-on-top exists so that separation restrictions normally applied by ATC can be temporarily suspended. An aircraft cleared to operate 1000’-on-top provides its own separation for other IFR aircraft—especially useful when two aircraft are transitioning to or from an approach when VFR conditions exist above cloud layers. Flying VFR, however, placed the responsibility for maintaining safe separation from other aircraft upon Gandy and Ritner, a procedure referred to as "see and be seen," since changed to "see and avoid." Upon receiving the "1,000 on top" clearance, Captain Gandy increased his altitude to 21,000 feet.〔 Both crews had estimated that they would arrive somewhere along the Painted Desert line at about 10:31 am Pacific time.〔CAB Docket 320, File 1, History of Flights, Section 1, Paragraph 5, issued 1957/04/17〕〔CAB Docket 320, File 1, History of Flights, Section 2, Paragraph 5, issued 1957/04/17〕 The Painted Desert line was about 200 miles long, running between the VORs at Bryce Canyon, Utah and Winslow, Arizona at an angle of 335 degrees relative to true north—wholly outside of controlled air space. Owing to the different headings taken by the two planes, TWA's intersection of the Painted Desert line, assuming no further course changes, would be at a 13-degree angle relative to that of the United flight, with the Constellation to the left of the DC-7. As the two aircraft approached the Grand Canyon, now flying at the same altitude and nearly the same speed, the pilots were most likely maneuvering around towering cumulus clouds, though flying VFR required the TWA flight remain in clear air at all times. As they were maneuvering near the canyon, it is believed the planes simultaneously passed the same cloud formation on opposite sides, setting the stage for the collision.〔''Blind Trust'', by John J. Nance, William Morrow & Co., Inc. (USA), 1986, ISBN 0-688-05360-2, PP 90-92〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「1956 Grand Canyon mid-air collision」の詳細全文を読む スポンサード リンク
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