1956 Grand Canyon mid-air collision

The 1956 Grand Canyon mid-air collision occurred on Saturday, June 30, 1956 at 10:30 AM Pacific Standard Time when a United Airlines passenger airliner struck a Trans World Airlines (TWA) airliner over the Grand Canyon in Arizona, resulting in the crash of both planes and 128 fatalities. Until the 1960s it was the deadliest airline crash in history, and would lead to sweeping changes in the regulation of flight operations over the United States.

Flight history
United Airlines Flight 718, a Douglas DC-7 Mainliner named Mainliner Vancouver, and piloted by Captain Robert Shirley and First Officer Robert Harms, 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 northeast of Palm Springs, California where he turned left toward a radiobeacon near Needles, California, after which his flight plan was direct to Durango in southwestern Colorado. The DC-7, although still operating under IFR, was now "off airways"-that is, flying in uncontrolled airspace.

TWA Flight 2, a Lockheed L-1049 Super Constellation named Star of the Seine, with pilot Jack Gandy and copilot James Ritner in the cockpit, departed Los Angeles at 9:01 AM with 64 passengers 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. 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, invoking his authority to cancel his IFR flight plan and revert to visual flight rules (VFR), requested "1,000 on top" clearance, which was approved. "1,000 on top" clearance meant he could climb to an altitude sufficient to place his aircraft 1,000 feet above the cloud tops along his flight path. 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." 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. 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, now flying at the same altitude and nearly the same speed, approached the Grand Canyon, the pilots were forced to weave around towering cumulus clouds, as flying in uncontrolled airspace required that they 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.

Collision
At about 10:30 AM the flight paths of the two aircraft intersected over the canyon and they collided at a closing angle of about 25 degrees. Post-crash analysis determined that the United DC-7 was banked to the right and pitched down at the time of the collision, suggesting that one or possibly both of the United pilots saw the TWA Constellation seconds before impact and that evasive action was attempted.

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 empennage (tail section) to break away from the rest of the airframe. Simultaneously, the propeller on the DC-7's left outboard (number one) engine chopped a series of gashes into the bottom of the Constellation's fuselage. Explosive decompression would have instantly occurred from the combined damage, a theory that was substantiated by light debris (e.g., cabin furnishings and personal effects) being scattered over a large area.

The separation of the empennage from the Constellation resulted in an immediate loss of control and the aircraft went into a near-vertical terminal velocity dive. Plunging into the canyon at an estimated speed of more than 700 feet (213.4 metres) per second (475 mph), the plane crashed inverted on the northeast slope of Temple Butte and disintegrated on impact. An intense fire ensued. The severed empennage, battered but still in a recognizable form, came to rest nearby.

The DC-7's left wing outboard of the number one engine was mangled by the impact and was no longer capable of producing substantial lift. The engine itself had been fatally damaged as well, and the combined loss of lift and propulsion put the crippled aircraft into a rapidly descending left spiral from which no recovery was possible. The Mainliner slammed into the south wall of Chuar Butte and burned.

Search and recovery
The airspace over the canyon was not under any type of radar surveillance and there were no homing beacons or "black boxes" (cockpit voice and flight data recorders) aboard either aircraft. The last position reports received from the flights did not reflect their locations at the time of impact. 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 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, futilely struggling with the controls, he implored the plane to "[Pull] up! [Pull] up!" (bracketed words were inferred by investigators from the context and circumstances in which they were uttered).

After a period of time had elapsed in which neither flight had reported a current position, the 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, 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. His brother and he 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.

Owing to the exceptional severity of the ground 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 Cemetery. Sixty-six of the seventy TWA passengers and crew are interred in a mass grave at Citizen's 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 remain at the crash sites.

Investigation
The investigation of this accident 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 realtime 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:


 * 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 the 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 evade 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 LIFE's April 29, 1957 issue and was subsequently included in David Gero's 1996 edition of Aviation Disasters II.

In a letter to Gero in 1995, Hunter wrote:


 * I was able to plot the two intersecting flight paths, and the fact that both planes were in each other's blind spot. I remember showing that the descending aircraft's propellers chewed a series of gashes along the fuselage top of the ascending aircraft. I did a lot of this type of factual re-creation for LIFE. They were always extremely tough to piece together to the satisfaction of all the editors, art directors and assorted researchers who were assigned to such projects. But, it was extremely interesting work.

Hunter's recollection of his illustration was not completely accurate. The painting showed the DC-7 below the Constellation, with the former's number one engine beneath the latter's fuselage, which agreed with the CAB technical findings.

Catalyst for change
Due to the substantial loss of life and the chain of events that led to it, the Grand Canyon tragedy was extensively covered by the press, both in the USA and abroad. As the story unfolded, the general public learned just how primitive ATC was and how little was being done to modernize it. The actions of the air traffic controller who had cleared TWA to "1,000 on top" were severely criticized, as he had not advised Captains Gandy and Shirley about the potential for a traffic conflict following the clearance, even though he would have had to have known of the possibility. The controller was publicly blamed for the accident by both airlines and was vilified in the press. However, he was subsequently cleared of any wrongdoing. As testified by Charles Carmody (the then-assistant ATC director) during the investigation, neither flight was legally under the control of ATC when they collided, as both were "off airways." Therefore, the controller was not required to issue a traffic conflict advisory to either pilot and was, in fact, prohibited from doing so.

The nature and timing of the accident was particularly alarming in that public confidence in air travel had substantially increased during the 1950s with the introduction of new generation airliners like the Super Constellation, DC-7 and Boeing Stratocruiser. Due to the performance and reliability of these planes, business travel by air had become routine for larger corporations, and vacationers often considered flying instead of traveling by train. Coincidentally at the time, a congressional committee was reviewing domestic air travel in general, as there was growing concern over the number of accidents being reported. However, little progress was being made and the state of ATC at the time of the Grand Canyon accident reflected the methods and technology of the 1930s.

As bureaucratic gridlock persisted, and near-misses and mid-air collisions continued to occur, the public became outraged and demanded that politicians do something more than talk about the problem. 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.

However, control of American airspace continued to be split between the military and the Civil Aeronautics Administration (CAA, the federal agency in charge of air traffic control at the time). The CAA had no authority over military flights, which could enter controlled airspace with little or no warning to other traffic. The unfortunate result of this arrangement was a series of near-misses and collisions involving civil and military aircraft, the latter often flying at much higher speeds than the former. For example, in 1958, the collision of a civil airliner and a fighter jet near Las Vegas, Nevada while the former was flying "on-airways" resulted in 49 fatalities.

Once again, action was demanded. Following more congressional hearings, the Federal Aviation Act of 1958 was passed into law, dissolving the CAA and creating the Federal Aviation Agency (FAA, later renamed Federal Aviation Administration). The FAA was given unprecedented and total authority over the control of American airspace, including military activity, and as procedures and ATC facilities were modernized, airborne collisions gradually subsided.

Dramatization
The story of the disaster was featured on the eighth season of Canadian National Geographic Channel show Mayday (known as Air Emergency in the US, Mayday in Ireland and Air Crash Investigation in the UK and the rest of world). The episode is entitled "System Breakdown."

Literary Reference
In his novel Skeleton Man (2004), Tony Hillerman uses this event as the backdrop to the plotted events of his story.