What happened
The flight departed Las Vegas for Denver under Instrument Flight Rules, carrying sufficient fuel for a five-hour flight. Enroute, the crew monitored deteriorating weather conditions at their destination. As the aircraft approached the Dupont Intersection north of Denver, reports indicated a ceiling of 200 feet and visibility of two miles. These conditions fell below the operator's landing minimums, prompting the crew to request a change of plans.
The flight was cleared to divert to Laramie, Wyoming, as the alternate airport. However, while approaching Laramie, the crew requested further clearance to proceed direct to Cheyenne due to a squall line between the two locations. At 1740, the aircraft reported over the Cheyenne range at 14,000 feet. A special weather report indicated the ceiling had dropped to 900 feet with light sleet and reduced visibility.
While proceeding along the east course of the Cheyenne range, the crew notified the tower that they were low on fuel, accumulating ice, and struggling to maintain altitude. Clearance was granted to descend to 8,000 feet on the north course. Shortly after acknowledging this instruction, the aircraft encountered severe turbulence. An unreadable transmission with signs of distress was heard by the tower at approximately 1750. Two minutes later, the crew reported they were out of the situation. Moments after this report, a noise consistent with an engine surge was heard northwest of the airport, followed by a flash of light two miles away.
Findings
The investigation determined that the aircraft lost control during an instrument approach to Cheyenne under conditions of heavy icing and severe turbulence. Key factors included:
- The wings and tail surfaces lacked deicing boots, although anti-icing equipment was installed on the propellers.
- Pre-departure forecasts indicated enroute icing conditions.
- A weather front moved toward Cheyenne faster than anticipated by both the Weather Bureau and the flight crew, arriving before a landing could be completed.