They departed Los Angeles at 9:04 am PST with 53 passengers and 5 crew members aboard (including two flight attendants), bound for Chicago's Midway Airport.

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.

[6][7] The Painted Desert line was about two hundred miles (320 km) 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.

[citation needed] 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.

The only immediate indication of trouble was when United company radio operators in Salt Lake City and San Francisco heard a garbled transmission from Flight 718 (the DC7), the last from either aircraft.

[citation needed] Civil Aeronautics Board (CAB) accident investigation engineers later deciphered the transmission – which had been preserved on magnetic tape – as the voice of co-pilot Robert Harms declaring, "Salt Lake, [ah], 718 ... we are going in!"

[12] During a trip earlier in the day, Palen had noted dense black smoke rising near Temple Butte, the crash site of the Constellation, but had dismissed it as brush set ablaze by lightning.

Numerous helicopter missions were subsequently flown down to the crash sites to find and attempt to identify victims, as well as recover wreckage for accident analysis, a difficult and dangerous process due to the rugged terrain and unpredictable air currents.

It is not possible to determine why the pilots did not see each other, but the evidence suggests that it resulted from any one or a combination of the following factors: Intervening clouds reducing time for visual separation, visual limitations due to cockpit visibility, and preoccupation with normal cockpit duties, preoccupation with matters unrelated to cockpit duties such as attempting to provide the passengers with a more scenic view of the Grand Canyon area, physiological limits to human vision reducing the time opportunity to see and avoid the other aircraft, or insufficiency of en route air traffic advisory information due to inadequacy of facilities and lack of personnel in air traffic control.In the report, weather and airworthiness of the two planes were thought to have played no role in the accident.

Lacking credible eyewitnesses and with some uncertainty regarding high altitude visibility at the time of the collision, it was not possible to determine conclusively how much opportunity was available for the TWA and United pilots to see and avoid each other.

Also worth noting was that the investigation itself was thorough in all respects, but the final report focused on technical issues and largely ignored contributory human factors, such as why the airlines permitted their pilots to execute maneuvers solely intended to improve the passengers' view of the canyon.

Hunter's finely detailed gouache painting first appeared in Life's April 29, 1957, issue[17] and was subsequently included in David Gero's 1996 edition of Aviation Disasters II.

In a letter to Gero in 1995, Hunter wrote:[note 3][citation needed] I was able to plot the two intersecting flight paths and the fact that both planes were in each other's blind spot.

The accident was covered by the press worldwide, and as the story unfolded, the public learned of the primitive nature of air traffic control (ATC) and how little was being done to modernize it.

"[20] The accident was particularly alarming in that public confidence in air travel had increased during the 1950s with the introduction of new airliners like the Super Constellation, Douglas DC-7, and Boeing Stratocruiser.

Often-contentious congressional hearings followed, and in 1957, increased funding was allocated to modernize ATC, hire and train more air traffic controllers, and procure much-needed radar – initially military surplus equipment.

For example, in 1958, the collision of United Airlines Flight 736 flying "on-airways" and an F-100 Super Sabre fighter jet near Las Vegas, Nevada, resulted in 49 fatalities.

The FAA was given total authority over American airspace, including military activity, and as procedures and ATC facilities were modernized, mid-air collisions gradually became less frequent.

The episode, entitled "Black Box UFO Secrets", contained the Universal Newsreel footage of the accident narrated by Ed Herlihy.

In 2015, the first season of Mysteries at the National Parks on the Travel Channel, in the series' seventh episode entitled, "Portal To The Underworld" the crash was also featured and was mentioned as being a "supernatural event."