1956 Grand Canyon mid-air collision

On June 30, 1956, a Lockheed L-1049A Super Constellation operating as TWA Flight 2, was struck by a Douglas DC-7 Mainliner operating as United Air Lines Flight 718 over Grand Canyon National Park, Arizona. The Constellation fell into the canyon, while the DC-7 slammed into a cliff. All 128 people on board both aircraft died, making it the first commercial airline incident to exceed one hundred fatalities. Both aircraft had departed Los Angeles International Airport minutes apart from each other and headed for Chicago and Kansas City, respectively.

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

Flight history

TWA 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 PST 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. Flight 2, initially flying under instrument flight rules (IFR), climbed to altitude 19000 ft 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 Air Lines Flight 718, a Douglas DC-7 named Mainliner Vancouver, was piloted by Captain Robert "Bob" Shirley (age 48), First Officer Robert Harms (36), and Flight Engineer Girardo "Gerard" Fiore (39). They departed Los Angeles at 9:04 am PST with 53 passengers and 5 crew members (including two flight attendants), bound for Chicago's Midway Airport. Climbing to an authorized altitude of 21000 ft, 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. United's DC-7, though still under IFR, was now, like TWA's Constellation, en route 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 flight 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 then requested "1,000 on top" clearance (flying 1000 ft above the clouds, and thus in visual meteorological conditions). This was approved by ATC, and meant that the Constellation was still under IFR but free of separation restrictions normally applied by ATC. It transferred to Gandy and Ritner the responsibility for maintaining safe separation from other aircraft, on the principle then termed "see and be seen" (more recently "see and avoid").

This division of responsibilities between aircrew and ATC is especially useful when two aircraft are transitioning to or from an airfield approach when VFR conditions exist above cloud layers. It is less common en route.

Upon receiving "1,000 on top" clearance, Captain Gandy increased his altitude to 21,000 ft. Both crews were then at this altitude, and both had estimated that they would cross the Painted Desert line at about 10:31 am Pacific time. The Painted Desert line was about 200 mi 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 crossing 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, at the same altitude and nearly the same speed, the pilots were likely maneuvering around towering cumulus clouds. (The Constellation's clearance required it to stay in clear air – and above cloud.) As they were maneuvering near the canyon, it is believed the planes passed the same cloud on opposite sides.

Accident

At 10:32 am, the two aircraft collided over the canyon at an angle of about 25 degrees. Post-crash analysis determined that the United DC-7 was banking to the right and pitching down at the time of the collision, suggesting that one or possibly both of the United pilots spotted the TWA Constellation and attempted evasive action.

The DC-7's upraised left wing clipped the top of the Constellation's vertical stabilizer and struck the fuselage immediately ahead of the stabilizer's base, causing the tail assembly to break away from the rest of the airframe. The propeller on the DC-7's left outboard, or number one engine, concurrently chopped a series of gashes into the bottom of the Constellation's fuselage. Explosive decompression would have instantaneously occurred from the damage, a theory substantiated by light debris, such as cabin furnishings and personal effects, being scattered over a large area.

The separation of the tail assembly from the Constellation resulted in immediate loss of control, causing the aircraft to enter a near-vertical, terminal velocity dive. Plunging into the Grand Canyon at an estimated speed of more than 700 ft/s, the Constellation slammed into the north slope of a ravine on the northeast slope of Temple Butte and disintegrated on impact, instantly killing all aboard. An intense fire, fueled by aviation gasoline, ensued. The severed tail assembly, badly battered but still somewhat recognizable, came to rest nearby.

The DC-7's left wing to the left of the number one engine was mangled by the impact and was no longer capable of producing substantial lift. The engine had been severely damaged as well, and the combined loss of lift and propulsion left the crippled airliner in a rapidly descending left spiral from which recovery was impossible. The Mainliner collided with the south side cliff of Chuar Butte and disintegrated, instantly killing all aboard.