United Air Lines Flight 736

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 April 21, 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 mid-air collision with a United States Air Force fighter jet crewed by two pilots. Both aircraft fell out of control from 21,000 ft 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 $1.45 million 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. On April 21, 1958, it departed Los Angeles International Airport at 7:37 a.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 50 mi 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 7:45 a.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 28,000 ft, 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 8:14 a.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 8:31 a.m. arrival time over McCarran Field near Las Vegas. At 8:28 a.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 14,000 ft. As the fighter descended in a southerly direction, the airliner was approaching Las Vegas air space at about 312 kn on a north-northeasterly heading of 23 degrees, flying straight and level within the confines of its designated "Victor 8" airway. 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 8:30 a.m., in clear weather with excellent visibility of over 35 mi, the flight paths of the two aircraft intersected about 9 mi southwest of Las Vegas. The converging aircraft collided nearly head-on at an altitude of 21,000 ft at an estimated closure speed of 665 kn.

The descending Air Force jet, flying at 444 kn, 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 90 degree 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 8:30 a.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 8 ft 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 2.6 mi 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, 5.4 mi 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.

Crash sites

The 49 lives lost in this mid-air collision made it the deadliest aviation incident in the history of the Las Vegas region, but the area has experienced two other major airliner crashes. Movie star Carole Lombard and 21 others died in the mountainside crash of Transcontinental & Western Air (TWA) Flight 3 in 1942, about 16 mi WSW of where United Airlines Flight 736 crashed.

In 1964, 29 people died when Bonanza Air Lines Flight 114 flew into a hilltop 5 mi SW of the Flight 736 impact site, close to where the F-100F crashed six years earlier.

At both of those rugged, mountainous sites, salvage efforts removed the more accessible wreckage, but scattered portions of the TWA Douglas DC-3 and Bonanza Air Lines Fairchild F-27 were left behind, including the DC-3's radial engines. The United Airlines DC-7 crash site, however, had been cleared of all but the smallest artifacts due to its generally flat terrain. In 1958 the site was unpopulated desert a mile or more from the nearest paved road, but starting around 1999 it became threatened by encroaching development. Today the spot where the DC-7 crashed is adjacent to the neighborhood of Southern Highlands near the intersection of Decatur Boulevard and Cactus Avenue, amid commercial development. A small engraved metal cross placed in the sandy soil in 1999 by the son of a victim remained the only sign of the loss of United Airlines Flight 736, but preliminary efforts were in motion to encourage public officials to build a permanent memorial to those who died.

A brief video produced by the Las Vegas Review-Journal in April 2018 says the site where Flight 736 impacted is now beneath a parking lot, but the metal cross was still standing nearby on a low hill that remained undeveloped.