United Air Lines Flight 736 was a scheduled American transcontinental passenger service flown daily by United Airlines between Los Angeles and New York City. On April21, 1958, the airliner assigned to the flight, a Douglas DC-7 with 47 on board, was flying over Clark County, Nevada in clear weather when it was involved in a daytime with a United States Air Force fighter jet crewed by two pilots. Both aircraft fell out of control from and crashed into unpopulated desert terrain southwest of Las Vegas, leaving no survivors. The loss of Flight 736, one of a series of 1950s mid-air collisions involving passenger aircraft in American skies, helped usher-in widespread improvements in air traffic control within the United States, and led to a sweeping reorganization of federal government aviation authorities.
Among the DC-7 passengers were a group of military personnel and civilian contractors involved with sensitive Department of Defense weapons systems. Their deaths triggered new rules prohibiting similar groups engaged in critical projects from flying aboard the same aircraft.
The official investigation report cited cockpit visibility limitations and high closure speeds as contributing to the accident. While the report did not assign blame for the collision to either flight crew, it faulted military and civilian aviation authorities for not reducing well-known collision risks that had existed for over a year within the confines of airways, even after numerous complaints from airline crews.
A series of lawsuits were filed following the collision. In one case a judge stated the Air Force pilots did not use "ordinary care" in operation of the fighter jet, and should have yielded the right of way to the DC-7 airliner, despite the investigation assigning no blame to either flight crew for the collision. The judge also criticized the Air Force for not coordinating their training flights with civilian traffic, and for failing to schedule their flights to minimize traffic congestion. In another case, a settlement was reached where the U.S. Government paid United Airlines $1.45million in compensation.
Events leading to the accident The Flight 736 aircraft was a four-engine DC-7 propliner that entered the United Airlines fleet in early 1957, registered as N6328C. (Note: registration N6328C was reassigned to another aircraft in 1997) On April 21, 1958, it departed Los Angeles International Airport at 7:37a.m. on a scheduled transcontinental flight to New York City, with stopovers in Denver, Kansas City, and Washington, D.C. The flight crew were Captain Duane Mason Ward, age 44, First Officer Arlin Edward Sommers, 36, and Flight Engineer Charles E. Woods, 43. Of the 42 passengers on the flight, seven were military personnel and 35 were civilians.
Soon after taking off, the airliner was directed about east through controlled airspace to a waypoint over Ontario, California, where a turn to the northeast towards Las Vegas allowed it to merge with the "Victor 8" airway. The United Airlines crew–using radio call sign "United 7-3-6"–flew the DC-7 under instrument flight rules (IFR), controlled by Civil Aeronautics Authority (CAA) ground stations, at an authorized cruise altitude of 21,000 feet toward the first stopover at Denver.
Approximately eight minutes after the DC-7 departed Los Angeles, a U.S. Air Force F-100F-5-NA Super Sabre jet fighter, serial number 56–3755, took off from Nellis Air Force Base near Las Vegas at 7:45a.m. on a training flight with two pilots on board. In the front seat of the tandem cockpit was flight instructor and safety pilot Captain Thomas Norman Coryell, 28. Behind him was his trainee, First Lieutenant Jerald Duane Moran (misnamed Gerald in early reports), 23. As part of his IFR training, Moran would spend the flight under a sliding hood that blocked his view outside the aircraft, but allowed him to see his instrument panel. The purpose of the hood was to force the trainee pilot to fly using instruments alone, simulating flight in darkness or in clouds which can deprive a pilot of external visual clues.
The duties of the front-seat pilot were to maintain a lookout for other aircraft while instructing and monitoring the performance of the trainee in the rear seat. The F-100F had dual pilot controls that allowed the instructor at any time to take over flying the jet. Part of the training flight involved a descent and approach to Nellis Air Force Base from an altitude of , with an extended speed brake, under simulated instrument meteorological conditions (IMC). The descent was to follow a "teardrop pattern," with the Las Vegas commercial radio station KRAM as the navigational fix, a process the Air Force called the "KRAM procedure." The prescribed descent angle for the KRAM procedure was about five degrees.
At about 8:14a.m. CAA controllers received a routine position report from Flight 736 while it was flying over a navigational radio beacon east of Daggett, California; the report estimated an 8:31a.m. arrival time over McCarran Field near Las Vegas. At 8:28a.m. the F-100F crew requested and received clearance from the military controller at Nellis Air Force Base to begin a procedural "jet penetration" descent to . As the fighter descended in a southerly direction, the airliner was approaching Las Vegas air space at about on a north-northeasterly heading of 23degrees, flying straight and level within the confines of its designated "Victor 8" airway.. Retrieved July 14, 2021. The CAA stations controlling the airliner were unaware of the fighter jet; the Air Force controller at Nellis Air Force Base directing the jet was unaware of the airliner.
Collision
At 8:30a.m., in clear weather with excellent visibility of over , the flight paths of the two aircraft intersected about southwest of Las Vegas. The converging aircraft collided nearly head-on at an altitude of at an estimated closure speed of .
The descending Air Force jet, flying at , had sliced through the airliner's right wing with its own right wing, immediately sending both aircraft out of control. At the moment of collision the F-100F was in a 90degree bank to the left at a down angle of approximately 15 to 17 degrees. One eyewitness to the collision said the wings of the F-100F "dipped" about two seconds before the collision; another eyewitness said that just before the impact, the fighter "swooped down." The witness descriptions and the extreme 90 degree bank of the fighter jet—far more than the 30 degrees outlined in the KRAM procedure—indicate an unsuccessful last-second evasive action by the Air Force crew.
Moments after the two planes collided, the only mayday distress call radioed by the United Airlines crew was heard at 8:30a.m. plus 20 seconds. The message as recorded by a ground station was "United 736, Mayday, mid-air collision, over Las Vegas." The crippled airliner—now missing about of its right wing—trailed black smoke and flames as it spiraled earthward in an unrecoverable spin. The high aerodynamic forces resulting from the spin exceeded the DC-7's stress limits, causing the engines to be wrenched from their mounts, and seconds later the remainder of the aircraft began breaking apart. The airliner and its associated debris fell onto a then-empty patch of desert outside the town of Arden, in what is now the unincorporated town of Enterprise, about northeast of the estimated collision location. The nearly vertical descent and subsequent explosion made the crash unsurvivable.
The fighter jet—its right wing and right tailplane torn away by the collision—left a trail of fragments as it arced steeply downward, rolling as it fell. One of the Air Force pilots called out an unrecorded mayday message that was eventually determined to be "Mayday, Mayday, this is seven-five-five, we're bailing out". The out-of-control jet crashed into a hilly area of uninhabited desert, SSW of the DC-7 crash site. At least one of the Air Force pilots was still in the jet when it hit the ground, but contemporary news reports differ on whether the other pilot attempted an unsuccessful low-altitude ejection, or stayed with the jet all the way to the ground. Witnesses reported seeing a parachute drifting away from the falling F-100F, leading to the hope that a pilot had ejected, but when the parachute was located it was determined to be a detached drag parachute that normally would be used to help the fighter slow down shortly after landing.
Investigations
At the request of the local sheriff and United Airlines, the Federal Bureau of Investigation sent fingerprint experts to help identify the human remains. Among the dead were 13 civilian and military managers, engineers and technicians assigned to the American ballistic missile program. Five of that group were civilian contractors attached to the missile program at Norton Air Force Base; they were en route to conferences at the headquarters of the Strategic Air Command at Offutt Air Force Base. Articles in the Las Vegas Review-Journal commemorating the 40th and 50th anniversaries of the crash reported the FBI search went beyond fingerprint matching for identification; the agents were also looking for any surviving sensitive papers relating to national security the group of military contractors had carried on board in handcuffed briefcases. The same reports also said the crash prompted the military and defense industry to adopt rules to keep groups of technical people involved in the same critical project from travelling together on the same plane.
Investigators from the Civil Aeronautics Board (CAB) conducted an accident analysis, and four months after the collision released a report on August19, 1958. The report ruled out the weather conditions and the airworthiness of the two planes as factors in the collision. The report stated the probable cause was the high rate of near head-on closure, and that at high altitude, there were human and cockpit limitations involved. The CAB investigation concluded a metal frame support on the F-100's canopy seriously interfered with the Air Force instructor pilot's ability to see the oncoming DC-7, while a supporting pillar on the DC-7's windshield could have prevented the United Airlines captain from sighting the fighter until it was too late to react; however, the report noted the view of the fighter from the airliner's copilot position was not obstructed by any supporting pillar.
The CAB report did not assign blame to either flight crew for the accident, but faulted authorities at the CAA and Nellis Air Force Base for failing to take measures to reduce a known collision exposure; training exercises were allowed to be conducted for more than a year prior to the collision within the confines of several airways, even after numerous near-misses with military jets had been reported by airline crews. The CAB acknowledged that the Air Force, following the accident, took numerous steps to reduce the collision exposure on the airway structure in the Las Vegas area. The report also stated the CAA started a civil-military coordination program, including a review of jet penetrations on a national scale.
Legacy
From June 1956 to May 1958—beginning with the high-profile Grand Canyon disaster and concluding with the loss of Capital Airlines Flight 300—in just under two years a total of 245 military and civilian people died in a series of five major United States mid-air collisions involving at least one passenger transport aircraft. After each collision more momentum would build to improve the way commercial and military flights were controlled in the United States, with pressure building from the public, the media, and from concerned airline pilots who openly talked about how maneuvering military jets would fly into busy civilian airways without warning.