Accident at Near Cheyenne, Wyoming, 9 Oct 1949

Accident narrative

On October 9, 1949, a Slick Airways C-46 cargo plane crashed while making an instrument approach to the airport at Cheyenne, Wyoming. The aircraft, operating as Trip 11-8, was demolished, and all three occupants were killed.

**The flight**

Trip 11-8 was a scheduled cargo flight from San Francisco, California, to Newark, New Jersey, with intermediate stops including Las Vegas, Nevada, and Denver, Colorado. The crew consisted of Captain Ralph Settle and First Officer Robert Seebers, both of whom had extensive experience in the C-46, and a company employee, Joseph Allen, riding as a passenger. The aircraft departed San Francisco at 0912 and arrived in Las Vegas under Visual Flight Rules.

During a 35-minute stop in Las Vegas, the aircraft was serviced with 370 gallons of fuel. The crew received weather forecasts indicating broken to overcast clouds between southwestern Utah and Denver, with light rain showers below 8,000 feet and light snow showers above. Icing was forecast in the clouds above the 8,000-foot freezing level. The aircraft was not equipped with wing or tail de-icer boots, though it did have propeller anti-icing equipment.

The flight was cleared under Instrument Flight Rules to Denver, with Laramie, Wyoming, designated as the alternate airport. It departed Las Vegas at 1403.

**Diversion and approach**

The flight progressed normally, reporting over Grand Junction and Eagle, Colorado, while climbing to 16,000 feet. At 1708, over the Dupont Intersection five miles north of Denver, the flight contacted the Denver Tower. The Denver ceiling was reported at 200 feet with two miles visibility. Because this was below the company's landing minimums of a 400-foot ceiling and one mile visibility, the crew requested a change of flight plan. They chose Rock Springs, Wyoming, as a new alternate, with permission to land at Laramie if weather permitted. Denver Air Traffic Control approved the change and cleared the flight to maintain 14,000 feet.

At 1732, when 25 miles south of Laramie, the flight called the Cheyenne Tower and asked to proceed direct to Cheyenne. Denver ATC approved this, and the tower advised the crew of a squall line between Laramie and Cheyenne. At that time, Cheyenne reported a 3,500-foot ceiling and 20 miles visibility.

By 1740, the flight was over the Cheyenne range at 14,000 feet. A special weather report was given to the crew indicating the ceiling had dropped to 900 feet with light sleet and 12 miles visibility. Proceeding outbound on the east course of the range, the crew notified the tower they were low on fuel, taking on ice, and having difficulty maintaining altitude. The flight was cleared to descend to 8,000 feet on the north course. Seconds after acknowledging this clearance, the aircraft encountered severe turbulence.

At approximately 1750, the tower heard an unreadable transmission characterized by definite hysteria. Several calls from the tower went unanswered. Two minutes later, at 1752, the tower received a final transmission: "We are O.K and are out of it now." About half a minute later, the sound of surging engine power was heard northwest of the tower, followed shortly by a flash of light approximately two miles northwest of the airport.

**What the investigation found**

The wreckage was located on rolling terrain about two and a half miles northwest of the airport. Ground marks indicated the aircraft struck nose-first at an angle of approximately 45 degrees, with the landing gear retracted and flaps set one-quarter down. The impact tore the wings, engines, and left fuel tanks from the aircraft, scattering debris over 515 feet. The Board found no evidence of mechanical malfunction or structural failure prior to the crash.

Investigators recovered the aircraft's records, which showed an oxygen tank regulator had stuck open sometime after leaving San Francisco. This would have quickly exhausted the oxygen supply for the jump seat. However, there was no evidence the pilots were affected by a lack of oxygen; communicators noted that, aside from the single hysterical transmission, all other radio calls were clear and apparently made by persons in full command of their faculties.

A weather analysis showed a trough line had caused upslope winds and low ceilings in the area, and a squall had developed along the trough line in southeastern Wyoming. Neither the Weather Bureau nor the Flight Advisory Weather Service anticipated the rapid development and movement of this squall line, and they did not warn the flight. The Board noted that the storm moved so rapidly it reached Cheyenne before the flight could land, subjecting the aircraft to severe turbulence and heavy icing during its approach.

The Board found that the crew departed Las Vegas into forecast icing conditions without wing de-icer boots. Although ground temperatures at the crash site were above freezing and fire destroyed much of the wreckage, preventing ice from being found adhering to the structure, the weather data confirmed heavy icing conditions existed at the flight's altitude.

**Probable cause**

The Board determined that "the probable cause of this accident was the loss of control of the aircraft during an instrument approach to Cheyenne, Wyoming, under conditions of heavy icing and severe turbulence."