As shocking as they are, midair collisions have led to the implementation of new safety initiatives that have dramatically changed the aeronautical landscape. Such was the case with United Airlines Flight 736 which collided with a US Air Force fighter jet over Clark County, Nevada on April 21, 1958.
Two different aircraft, two different missions
There were several factors that contributed to this accident. The most obvious were the vastly different aircraft types and missions. The United Airlines flight was being operated by a Douglas DC-7 with 47 people onboard. The Air Force F100 fighter was occupied by two pilots: a student and his instructor.
The DC-7 was flying its first leg of a transcontinental passenger flight from Los Angeles to New York City (with scheduled stopovers in Denver, Kansas City, and Washington, DC), while the F100 was on a local training mission. At the time of the mid-air collision, the airliner was at a level cruise altitude while the fighter jet was performing a prolonged tactical descent as part of its training profile.
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The DC-7 (using a radio call sign “United 7-3-6”) departed Los Angeles International Airport at 07:37, and shortly after, was directed through controlled airspace to a waypoint over Ontario, California. The IFR flight plan called for a subsequent turn to the northeast towards Las Vegas. At this point, it would join the Victor 8 airway at a cruise altitude of 21,000 feet toward the first stopover at Denver.
The military training flight was planned to focus on instrument flying procedures, including a descent and approach to Nellis Air Force Base from an altitude of 28,000 feet. Called the “KRAM procedure” (because it navigated via the Las Vegas commercial radio station KRAM), this 5-degree descent profile required the use of extended speed brakes under simulated instrument meteorological conditions (IMC). The descent was to follow a teardrop pattern, with the radio station as the navigational fix.
Clear skis, obstructed views
While the type of mission each aircraft operated was a consideration during the accident investigation, a tertiary factor was the partially obstructed visibility in both cockpits.
The F-100 was flying a training flight, which included a considerable amount of simulated instrument navigation with the student pilot using a view limiting device often referred to as a “hood”. This required the instructor (seated in the front tandem seat) to take responsibility for monitoring his student’s progress as well as maintaining visual separation from other aircraft.
While this remains a typical way of training civilian and military pilots today, the lack of coordinated air traffic control surveillance was a significant factor in the tragic end of both flights.
The DC-7 was also known to have some issues with visibility in some areas of the cockpit, caused by some of the windscreen’s structural elements. In fact, another mid-air collision involving a United Airlines DC-7 near The Grand Canyon was partially attributed to cockpit visibility imitations.
Two sets of controllers managed each flight: civilian for United 736 and military for the fighter jet. Unfortunately, neither controller coordinated with the other. This would prove to be a fatal misstep. At about 08:14 civilian controllers received a position report from Flight 736 east of Daggett, California; the report estimated an 08:31 arrival time over McCarran Field near Las Vegas.
At 08:28, the F-100F crew requested and received clearance from a military controller at Nellis Air Force Base to begin the KRAM procedure descent to 14,000 feet. As the fighter descended to the South, the airliner was approaching Las Vegas airspace on Victor 8 on a north-northeasterly heading of 23 degrees. Since they were not in communication with military air traffic controllers, the civilian stations monitoring the airliner were unaware of the F-100.
At 08:30, in clear weather with excellent visibility, the flight paths of the two aircraft intersected about nine miles (14 km) southwest of Las Vegas. The aircraft collided nearly head-on at an altitude of 21,000 feet. The mangled airplanes fell to the ground forming a scattered debris area. Media coverage shocked the public and a slew of lawsuits were filed after the accident.
Deficiency in ATC leads to wide-sweeping changes
At the time this accident occurred, the Civil Aeronautics Authority (CAA) was in charge of managing the American airspace system. This entity was the forerunner of the Federal Aviation Administration (FAA) which was to be formed as a result of this mid-air collision.
As a result of its investigation, the Civil Aeronautics Board (CAB) concluded that there was a lack of “segregation” given between military operations and civil aircraft flights within the airway area. These findings greatly contributed to a major overhaul of the air traffic control system in the United States.
Key legislation was passed and President Dwight Eisenhower ordered the creation of the Federal Aviation Administration in August 1958. The result was a reorganization of air traffic control and management of the National Airspace System. Steps to create coordination between military and civilian controllers were taken. As a result, the number of mid-air collisions has diminished significantly over the last few decades.
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