Mid-air collision on June 30, 1956 over the Grand Canyon
Location of the collision
The Grand Canyon mid-air collision occurred in the western United States on 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. The first plane fell into the canyon while the other slammed into a rock face. All 128 on board both airplanes perished, making it the first commercial airline incident to exceed one hundred fatalities. The airplanes 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.
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 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, 31 minutes behind schedule. Flight 2, initially flying under instrument flight rules (IFR), climbed to an authorized altitude of 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", 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 aboard (including two flight attendants), bound for Chicago's Midway Airport. Climbing to an authorized altitude of , 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 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 . 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 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.
Collision.
At about 10:30 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 , 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.
Aftermath.
Search and recovery.
The airspace over the canyon was not under any type of radar observation and there were no homing beacons, cockpit voice recorders, or flight data recorders aboard either aircraft. The last position reports received from the flights did not reflect their locations at the time of the collision. Also, there were no credible witnesses to the collision itself or the subsequent crashes.
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. 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!" The shrill voice of Captain Shirley was heard in the background as, presumably futilely struggling with the controls, he implored the airplane to "[Pull] up! [Pull] up!" (bracketed words were inferred by investigators from the context and circumstances in which they were uttered).
After neither flight reported their current position for some time, the two aircraft were declared to be missing, and search and rescue procedures started. The wreckage was first seen late in the day near the confluence of the Colorado and Little Colorado Rivers by Henry and Palen Hudgin, two brothers who operated Grand Canyon Airlines, a small air taxi service. 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.
However, upon hearing of the missing airliners, Palen decided that what he had seen might have been smoke from a post-crash fire. He and his brother flew a light aircraft (a Piper Tri-Pacer) deep into the canyon and searched near the location of the smoke. The Constellation's empennage was found, and the brothers reported their findings to authorities. The following day, the two men pinpointed the wreckage of the DC-7. 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.
The airlines hired the Swiss Air-Rescue and some Swiss mountain climbers to go to the scene where the aircraft fuselages had crashed. They were to gather the remains of the passengers and their personal effects. This was given considerable publicity in U.S. news releases at the time because of the ruggedness of the terrain where the fuselages came to rest.
Owing to the great violence of the impacts, no bodies were recovered intact and positive identification of most of the remains was not possible. On July 9, 1956, a mass funeral for the victims of TWA Flight 2 was held, at the canyon's south rim. Twenty-nine unidentified victims of the United flight were interred in four coffins at the Grand Canyon Pioneer Cemetery. Sixty-six of the seventy TWA passengers and crew are buried in a mass grave at Citizens Cemetery in Flagstaff, Arizona. A number of years elapsed following this accident before most of the wreckage was removed from the canyon. Some pieces of the aircraft still remain at the crash sites.
Investigation.
The investigation of this accident, led by Jack Parshall, was particularly challenging due to the remoteness and topography of the crash sites, as well as the extent of the destruction of the two airliners and the lack of real-time flight data as might be derived from a modern flight data recorder. Despite the considerable difficulties, CAB experts were able to determine with a remarkable degree of certainty what had transpired and, in their report, issued the following statement as probable cause for the accident:
 ;templatestyles src="Template:Blockquote/styles.css" / ;The Board determines that the probable cause of this mid-air collision was that the pilots did not see each other in time to avoid the collision. 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.
Neither flight crew was specifically implicated in the CAB's finding of probable cause, although the decision by TWA's Captain Gandy to cancel his IFR flight plan and fly "1,000 on top" was the likely catalyst for the accident. 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. It would not be until the late 1970s that human factors would be as thoroughly investigated as technical matters following aerial mishaps.
During the investigation, Milford "Mel" Hunter, a scientific and technical illustrator with "Life" magazine, was given early and unrestricted access to the CAB's data and preliminary findings, enabling him to produce an illustration of what likely occurred at the moment of the collision. Hunter's finely detailed gouache painting first appeared in