The Grand Canyon mid-air collision occurred on June 30, 1956, when a Trans World Airlines Lockheed L1049 Super Constellation (TWA 2) struck United Airlines Douglas DC-7 (United 718) over the Grand Canyon National Park. All 128 on board both flights perished, making it the first commercial airline crash to result in more than 100 deaths.

Grand Canyon Arizona

 

 

 

Flight history
Trans World Airlines Flight 2, a Lockheed L-1049 Super Constellation departed Los Angeles on Saturday, June 30, 1956 at 0901 PDT with 64 passengers for Kansas City Airport. The flight under instrument flight rules (IFR), climbed to an altitude of 19,000 feet and stayed in controlled airspace as far as Daggett, California. Captain Gandy requested permission to climb to 21,000 feet to avoid thunderstorms 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 then requested “1,000 on top” clearance (flying 1,000 feet 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.

Flying VFR placed the responsibility for maintaining safe separation from other aircraft upon Gandy and Ritner, a procedure referred to as “see and be seen,” since changed to “see and avoid.” Upon receiving the “1,000 on top” clearance, Captain Gandy increased his altitude to 21,000 feet.

At Daggett, Captain Gandy turned right to a heading of 059 degrees magnetic, toward the radio range near Trinidad, Colorado.

TWA Cockpit and Cabin Crew
Captain Jack Gandy, 41
First Officer James Ritner, 31
Flight Engineer Forrest Breyfogle, 37
2 Flight Attendants
Flight Engineer-off duty
11 TWA off duty employees on board with free pass

United Cockpit and Cabin Crew
Captain Robert Shirley 48
First Officer Robert Harms 36
Flight Engineer Gerard Fiore 39
2 Flight Attendants

United Airlines Flight 718, a Douglas DC-7 departed Los Angeles International Airport at 0904 PDT with 53 passengers bound for Chicago’s Midway Airport. Climbing to a cleared altitude of 21,000 feet, 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, like the Constellation, flying in uncontrolled airspace.

Both crews had estimated that they would arrive somewhere along the Painted Desert line at about 1031 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 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, now at the same altitude and nearly the same speed, the pilots were likely manoeuvring around towering cumulus clouds, though flying VFR required the TWA flight to stay in clear air. As they were manoeuvring near the canyon, it is believed the planes passed the same cloud on opposite sides, setting the stage for the collision.

Collision
At about 1030 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 stabiliser and struck the fuselage immediately ahead of the stabiliser’s base, causing the empennage (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 empennage 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 477 mph (700 feet per second (210 m/s)), the Constellation slammed into the north slope of a ravine located on the northeast slope of Temple Butte and disintegrated on impact, instantly killing all aboard. An intense fire, fuelled by aviation gasoline, ensued. The severed empennage, badly battered but still somewhat recognisable, came to rest nearby.

The DC-7’s left wing to the left side of the number one engine was mangled by the impact and was no longer capable of producing substantial lift. The engine itself 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, again killing all aboard in an instant.

Search and recovery
The airspace over the canyon was not under any type of radar contact and there were neither homing beacons nor “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 neither flight reported their current position for a while, 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. 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 Pioneer Cemetery. Sixty-six of the seventy TWA passengers and crew are interred 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 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 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:

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 which  resulted from any one or a combination of the following factors:

1. Intervening clouds reducing time for visual separation
2. Visual limitations due to cockpit visibility
3. Preoccupation with normal cockpit duties
4. Preoccupation with matters unrelated to cockpit duties such as attempting to provide the passengers with a more scenic view of the Grand Canyon area
5. Physiological limits to human vision reducing the time opportunity to see and avoid the other aircraft
6. Insufficiency of en route air traffic advisory information due to inadequacy of facilities
7. 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 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 manoeuvres 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.

1957 Government Study found no enroute radar use. Pilots talked through company radio operators who then relayed to ATC and back to pilots vis the same process. Use of uncontrolled airspace resulted in no separation of air traffic. The only way to ascertain presence of opposite traffic was look and see.

In April and May 1958 two mid air collision occurred over the US. Legislation brought the FAA Act of 23 Aug 1958 which:

• VFR on top procedure was denied
• Above 18000 feet Class A airspace was established, where an IFR flight plan was required. Class A meant it was a controlled airspace.
• Controlled Airways were increased by adding 375 VORs
• 82 Long range radars added

Change
At 128 fatalities, the Grand Canyon collision became the deadliest U.S. commercial airline disaster and deadliest air crash on U.S. soil of any kind, surpassing United Airlines Flight 409 the year before. It was surpassed in both respects on December 16, 1960, by the 1960 New York mid-air collision (another case involving United and TWA aircraft).

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 modernise it. The air traffic controller who had cleared TWA to “1,000 on top” was severely criticised, as he had not advised Captains Gandy and Shirley about the potential for a traffic conflict following the clearance, even though he must have known of the possibility. The controller was publicly blamed for the accident by both airlines and was vilified in the press, but he was cleared of any wrongdoing. As Charles Carmody (the then-assistant ATC director) testified during the investigation, neither flight was legally under the control of ATC when they collided, as both were “off airways”. The controller was not required to issue a traffic conflict advisory to either pilot and was, in fact, prohibited from doing so. According to the CAB accident investigation final report, Page 8, the en route controller relayed a traffic advisory regarding United 718 to TWA’s ground radio operator: “ATC clears TWA 2, maintain at least 1,000 on top. Advise TWA 2 his traffic is United 718, direct Durango, estimating Needles at 0957.” The TWA operator testified that Captain Gandy acknowledged the information on the United flight as “traffic received.

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. Travel by air had become routine for large corporations, and vacationers often considered flying instead of traveling by train. At the time, a congressional committee was reviewing domestic air travel, as there was growing concern over the number of accidents. However, little progress was being made and the state of ATC at the time of the Grand Canyon accident reflected the methods of the 1930s.

As near-misses and mid-air collisions continued, the public demanded action. Often-contentious congressional hearings followed, and in 1957 increased funding was allocated to modernise 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 no warning to other traffic. The result 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 United Airlines Flight 736 flying “on-airways” and an F-100 Super Sabre fighter jet near Las Vegas, Nevada resulted in 49 fatalities.

Again action was demanded. After more hearings the Federal Aviation Act of 1958 was passed, dissolving the CAA and creating the Federal Aviation Agency (FAA, later renamed the Federal Aviation Administration in 1966). The FAA was given total authority over American airspace, including military activity, and as procedures and ATC facilities were modernised, mid-air collisions gradually became less frequent.

TWA route is in red

United 718 flight route

Accident was inevitable 30 minutes ahead of collision; 128 fell to their death

Courtesy of Wikipedia.org; JTW Pilot Channel