April 21, 1958, United Air Lines / USAF, Douglas DC-7 (N6328C) / North American F-100F (56-3755) Mid-Air Collision near Las Vegas, NV
United Air Lines Flight 736, a DC-7 (N6328C), departed with 47 passengers and crew from Los Angeles (LAX) at 7:37 AM. Flight 736 was on a transcontinental flight to New York City (Idlywild) with a planned cruising altitude of 21,000 feet.
At about 7:45 AM, a US Air Force North American F-100F-5-NA Super Sabre fighter (56-3755) took off from Nellis AFB on an instrument training flight. During the exercise the flight was executing a simulated jet penetration in the area of Las Vegas, NV. At 8:30 AM, the fighter plane pilot reported that they were descending from 28,000 feet near the KRAM radio station. At the same time, United flight 736 was approaching the Las Vegas VOR.
Both aircraft collided head-on at 21,000 feet, nine miles southwest of the Las Vegas VOR station on Victor Airway 8. Initial contact occurred between the leading edge of the DC-7's starboard wing and the leading edge of the F-100's starboard wing. It was determined during the Civil Aeronautics Board (CAB) accident investigation that the DC-7 was flying at about 312 knots on a 023 degree heading and the F-100 at 444 knots on a 145 degree heading. Assuming a small descent angle of the F-100, the closure speed was close to 700 knots.
Both planes crashed out of control with the DC-7 entering a steep spiral dive. During the dive, three of the DC-7's four radial engines separated prior to impact. All persons on board both aircraft were killed.
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HISTORICAL SUMMARY:
The collision created two aircraft impact sites separated by seven miles, in addition to a large debris field between the two sites. During 1995, after much research and an extensive ground search, the DC-7 engine impact site was located. This discovery along with the discovery of the F-100F crash site by Craig Fuller of AAIR allowed the triangulation of the DC-7 main impact site.
When we first examined the DC-7 impact site, it appeared to be undisturbed with little evidence that an impact even took place. Reviewing old aerial photos, we decided to dig some test pits which revealed that the site (burned impact area) had been covered with a layer of top soil after the initial recovery work had been completed in 1958. The top soil not only concealed the site, but also formed a protective barrier from exposure. In effect it was a time capsule. However, with the population of Las Vegas growing, it was inevitable that the DC-7 impact site was in the path of future development.
Working with the landowner, we adopted a plan to map, excavate, document, and preserve the wreckage material we could recover. Over the following three years we excavated an area about 40 feet by 30 feet using a series of grids to mark not only where we excavated but also help document where we located items of interest. As a result, we recovered and documented hundreds of historical items during the excavations. Within a few short years the crash site of United Air Lines Flight 736 would be replaced by several commercial buildings and homes.
**UPDATE** June 2008, I visited the impact site of UAL Flight 736. A backhoe tractor had excavated a series of utility line trenches in front of the auto-tire center that was under construction. Visible in the freshly cut trench walls were the burned remnants of the DC-7 still covered in the top soil from 1958. I returned the next day and the trenches had been filled in.
On one trip to the debris field, I discovered an old weather balloon radiosonde.
According to the paperwork inside, the balloon was launched from Desert Rock, Nevada during February 2001.
I discovered it five years after it's launch and it was well weathered.
The Las Vegas Strip with it's casinos and hotels can be seen 12 miles away to the north. (LostFlights)
DEBRIS FIELD - DECEMBER 2010
DC-7 ENGINE IMPACT SITE(S):
This aerial photo taken during 1994, showing the location of the DC-7's main impact site and where the DC-7's three separated engine impact sites were located.
During 1958, this area was open desert with few if any dirt roads.
The DC-7's three engine impact sites were located by finding small concentrations of engine components and fragments that were left behind.
Fragments located within the engine impact area included engine ignition and exhaust components.
This fragment is part of an engine oil tank.
Each engine impact site location was recorded using GPS.
DOUGLAS DC-7 MAIN IMPACT SITE:
With the exception of a one lane dirt road (Cactus Road), the impact site of the DC-7 had remained untouched since 1958.
A concentration of exposed surface fragments littered the impact site, but most of the small wreckage debris was buried on-site by United Air Lines.
EXCAVATION OF FLIGHT 736 BEGINS - 1995:
Doug Scroggins documenting the excavation of United Flight 736 for a Lost Birds episode.
Recovery work began during late 1995 using the standard conventional archaeological grid method of excavation. Each grid was excavated and artifacts recovered were mapped as to their location.
As work progressed, we came to realize that the entire DC-7 impact site had been buried shortly after accident.
During the summer months, work on the site began in the early morning hours and ended at noon to avoid the 100 degree plus temperatures.
Doug Scroggins excavating below the sterile sub-surface layer down to the burn or "contact layer" where many historical artifacts were located and recovered.
The contact layer revealed a time capsule of items.
By June 2002, the housing development had been built on the south side of Cactus Road.
A simple metal cross served as the memorial.
Doug Scroggins examining a flight instrument drive gear at the DC-7 main impact site.
Excavation diagram illustrating the grids excavated during the recovery operation of the DC-7 main impact site during 1995-1997.
The remains of a small plastic wing from a toy DC-7 airplane.
These toy airplanes were given to child passengers by the airline stewardesses and pilots.
GIVING WAY TO PROGRESS:
By January 2001, construction had already begun for new housing and commercial developements.
Cactus Road was being transformed from a one way dirt road to a four lane paved city street.
The mounds of piled soil mark the location of our excavation work. Even though our excavation work was completed, we were still finding interesting aircraft items and personal effects on the surface.
June 2008. Construction begins on commercial developments that will in effect cover the remainder of the United Flight 736 main impact site.
UNITED FLIGHT 736 BURIED AGAIN:
When construction began on a business located on the DC-7 impact site, a series of utility trenches were excavated in front of the building.
The trenches exposed a contact layer of burned impact debris that was previously unknown and untouched.
The burned strata was visible in many of the utility trench walls.
The burn layer was visible approximately 12" to 18" below the sterile sub-surface.
The debris within the strata was consistent with our previous excavation of the site. This layer however was almost three times deeper.
The dark charcoal appearance within the east/west trench wall marks the burned debris of United Flight 718.
Within two days all of the trench lines were re-filled and eventually covered with pavement for a parking lot.
ARTIFACT ANALYSIS:
I used this ex-Delta Air Lines Douglas DC-7B (N4889C) stored in Chandler Arizona to match the location of recovered parts from UAL Flight 736.
The same aircraft was also used by LostFlights to identify located wreckage from UAL Flight 718 that was lost in the 1956 Grand Canyon disaster.
Fragment #1. Photographed in the lab. A closeup photo showing the popped rivets and contact compression fracture on a F-100F wing fragment that was located in the debris field.
FRAGMENT #2 - DOUGLAS DC-7 WING PANEL
Fragment #2 measures about 8.5" in length and was located during a search of the debris field in 1996.
The fragment has a structural shear on the left side while the right side of the fragment exhibits structural bending and fractures from being torn from the remaining right wing of the DC-7.
The red circle gives reference to the original location fragment #2 on the DC-7's right wing.
This photo also illustrates the catastrophic damage inflicted on the DC-7's outer wing structure and aileron flight control surface. The collision caused separation of the outer wing which removed a significant amount of lift and stability.
Control loss was further enhanced by the loss of the entire right aileron. Within a few seconds after the collision, the DC-7 rolled into a descending right spiral with no possibility of recovery. (LostFlights. org)
A closeup view of the sheared edge of fragment #2.
This recovered knob from Flight 736 was originally located on the Cabin Pressurization Control Indicator from the Flight Engineer's main panel.
A Cabin Pressure Controller Indicator from a Douglas DC-7.
A portion of fragmented newspaper from the DC-7 main impact site.
Data placard from one of the DC-7's four fuel quantity gauges.
