The final accident report identified the probable cause as "a sudden emergency of undetermined origin under adverse weather conditions resulting in rapid descent and impact with the ground at high speed".

At 9:00 A.M., a third Western Airlines flight, a DC-3 operating Flight 53 from Cheyenne, Wyoming to Great Falls, Montana, encountered moderate to severe air turbulence and moderate wing icing while approaching Douglas, Wyoming in the vicinity of Casper, and turned around to land back in Cheyenne.

[1]: 4 As Flight 34 approached Casper, the crew elected to overfly the scheduled stop and proceed to Rapid City due to the conditions.

[1]: 4  The air route traffic control center issued a new clearance to descend to 13,000 feet (4,000 m) and proceed to Rapid City via the Blue 37 and Red 2 airways.

[8] At 10:25 A.M., the flight reported its position over the Wright Junction intersection at 17,000 feet and estimated its arrival at Rapid City at 10:50 A.M.[4] The airline company radio operator gave the 9:30 en route weather update and the 10:10 Rapid City terminal weather update, which was acknowledged by the crew at 10:27.

[1]: 1–2 The initial hope was that the aircraft had developed radio problems, had passed over Rapid City, and continued on to Minneapolis or to the eastern part of South Dakota where weather conditions were better.

[10] The planes searched Friday afternoon and through the night, flying along the route dropping high intensity flares to illuminate the area.

[3][10] Light snow squalls prevented small aircraft from searching the Black Hills area of South Dakota, but the weather cleared up by the afternoon.

Ground search efforts initially focused on an area about 20 miles (30 km) west of the South Dakota border, about 60 miles (100 km) southeast of Gillette, because a rancher had reported hearing a low-flying plane in the area just minutes after the missing aircraft had reported its position at Wright Junction.

[3] In Deadwood, South Dakota, the Sheriff's office directed a ground search involving 50 men after a resident reported seeing a flare in the area on the night of the crash.

[8] A ham radio operator from Hot Springs, South Dakota reporting hearing faint SOS signals from the Elk Mountain region in southern Wyoming.

Officials looked into the report, but were skeptical of it because any survivors would have been able to build a fire that was visible from the air much easier than it would have been for them to improvise radio equipment to send distress signals.

[11] The pilots called in the location of the crash site to Rapid City at 4:05 P.M., after most of the private search planes had already returned to their bases.

[11] The next morning, aerial searchers returned to the area and relocated the wreckage about one-half mile (zero point eight zero kilometers) southwest of Bacon Creek.

[12][1]: 2  Western Air Lines officials said that the location of the wreckage showed that the aircraft was flying on course along the scheduled route when it crashed.

[11] That team arrived on March 1, but it was limited by the weather conditions, which included freezing temperatures, high winds, and snow.

[19] Investigators on the ground gathered mail that the aircraft had been carrying, and brought anything that was still intact to the Gillette Post Office for forwarding.

Because it had been snowing heavily when the plane crashed, there were no eyewitnesses, but investigators identified twelve people who had heard an aircraft flying overhead on the morning of the accident.

[20]: 1  Further investigation of the wreckage did not turn up any evidence of structural failure or malfunction of the control surfaces, and both engines appeared to have been working.

[1]: 3  The radio equipment was set to the correct frequencies, the cockpit instruments appeared to be functioning, and the heat and anti-icing valves were found in the operating position.

[1]: 2 Investigators did, however, discover three small pieces of ice, about the size of a man's little finger, inside one of the engine carburetors at the scene of the crash.

The finding raised the question of whether ice buildup in the air intakes had caused the engines to lose power, but pilots experienced with the type of aircraft testified that the Convair aircraft was designed with a very effective carburetor heat system to fight icing in extreme conditions.

[1]: 6–7  There was a possibility that there was malfunction of the control system in flight, such that caused by ice or another object becoming lodged and later breaking loose at the time of impact.

[1]: 7 Eventually, CAB investigators were only able to determine the probable cause of the crash as "a sudden emergency of undetermined origin under adverse weather conditions resulting in rapid descent and impact with the ground at high speed".