Investigation Summary
The flight was operating the Salt Lake City to Denver segment of a transcontinental service. After passing the Cheyenne radio range station, the crew was cleared to descend to 8,500 feet. To reach the WONT intersection, the flight was expected to intercept the 168 degree course of the Denver low frequency range. The crew initiated a right turn to a 210 degree intercept heading, which was a standard procedure. However, they failed to execute the subsequent left turn to track the airway. The investigation focused on the audio selector panel, suggesting the pilot may have inadvertently selected the Denver Visual Audio Range (VAR) instead of the low frequency range. Because both stations used the 'DEN' Morse code identifier, the crew may have heard the 'A' signal from the VAR and believed they had not yet reached the course line, leading them to fly directly into the mountains west of the airway. Investigators also considered a secondary possibility that the Automatic Direction Finder (ADF) had been affected by interference from the Fort Bridger radio range.
Final Conclusions
The Civil Aeronautics Board determined the probable cause was the failure of the flight to follow the prescribed route to Denver for reasons undetermined, continuing beyond the boundary of the airway into mountainous terrain. Contributing factors included the potential for audio signal confusion between two different navigation aids sharing the same identifier.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Captain J. R. Appleby
First Officer
First Officer H. G. Tower
Systems & Failure Modes
Audio Selector Panel
Used by the crew to select which navigation station identifiers were audible in their headsets.
Low Frequency Radio Range
The primary navigation aid intended for use to track the 168 degree course to Denver.
Visual Audio Range (VAR)
A secondary navigation aid that investigators believe the crew may have mistakenly tuned or listened to.
Interesting Facts
- 01The aircraft was a Douglas DC-6 named 'Mainliner Overland Trail'.
- 02The crash site was located approximately 50 miles north-northwest of Denver.
- 03The aircraft gouged a path 150 feet long by 50 feet wide through heavy timber before coming to rest.
- 04Both the Denver low frequency range and the Denver Visual Audio Range (VAR) used the same 'DEN' Morse code identifier at the time.
- 05The wreckage skidded 690 feet in total and burst into flames upon impact.
Safety Actions & Advisories
Identifier Modification
Following the investigation, the letter 'V' was added to the 'DEN' Morse code identifier for the Visual Audio Range (VAR) to prevent confusion with the Denver low frequency range.