1956 Grand Canyon Mid-Air Collision

The Grand Canyon mid-air collision occurred in the western United States on Saturday, June 30, 1956, when a United Airlines Douglas DC-7 struck a Trans World Airlines Lockheed L-1049 Super Constellation over Grand Canyon National Park, Arizona. All 128 on board both flights perished, making it the first commercial airline incident to exceed one hundred fatalities. The flights had departed

Los Angeles International Airport minutes apart for Chicago and Kansas City, respectively.

The collision took place in uncontrolled airspace, where it was the pilots' own responsibility to maintain separation ("See and avoid"). This highlighted the antiquated state of air traffic control, which became the focus of major aviation reforms.

Flight History (TWA Flight 2) (United Airlines Flight 718)
Trans World Airlines Flight 2, a Lockheed L-1049 Super Constellation named Star of the Seine, with Captain Jack Gandy (age 41), First Officer James Ritner (31), and Flight Engineer Forrest Breyfogle (37), departed Los Angeles on Saturday, June 30, 1956, at 9:01 am PDT 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 under instrument flight rules (IFR), climbed to an authorized altitude of 19,000 feet (5,800 m) 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. The Constellation was now "off airways", otherwise known as flying in uncontrolled airspace.

United Airlines Flight 718, a Douglas DC-7 named Mainliner Vancouver, and flown by Captain Robert Shirley (age 48), First Officer Robert Harms (36), and Flight Engineer Gerard Fiore (39), departed Los Angeles at 9:04 am PDT 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 (6,400 m), Captain Shirley flew under IFR in controlled airspace to a point 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 DC-7, though still under IFR jurisdiction, was now, just like the Constellation, flying in uncontrolled airspace.

Shortly after takeoff, TWA's Captain Gandy requested permission to climb to 21,000 feet to avoid thunderheads that were forming near 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 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 way to provide the horizontal separation required between two aircraft at the same altitude.

Captain Gandy requested "1,000 on top" clearance (flying 1,000 feet (300 m) above the clouds), which is still IFR, not VFR (visual flight rules), which 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.