Investigation Summary
The investigation centered on the navigational challenges faced by the crew in West Africa during the early 1950s. The Robertsfield radio beacon (NDB) operated on a frequency that was being interfered with by a more powerful beacon in Dakar, Senegal. At 03:01 UTC, the crew specifically reported this interference to the tower. Despite not having a positive fix on their position and being nearly 50 miles away from the airport, the captain initiated a descent from the en route altitude. The aircraft was in a clean configuration (flaps and gear retracted) and under power when it struck a hillside at 1,050 feet MSL. The Civil Aeronautics Board (CAB) found that the aircraft never actually reached the vicinity of Robertsfield, and the crew's belief that they were close enough to descend was a fatal navigational error.
Final Conclusions
The Civil Aeronautics Board determined the probable cause was the captain's action in descending below the en route minimum altitude without positive identification of the flight's position. Contributing factors included the radio interference between the Dakar and Robertsfield beacons, which likely provided the crew with misleading navigational cues.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Captain Frank James. He had been employed by Pan American since 1941.
First Officer
First Officer Paul Weaver.
Second Officer
Second Officer Thomas D. Burke.
Flight Engineer
Flight Engineer O. N. S. Schedel.
Systems & Failure Modes
Radio Beacon (NDB)
The primary navigational aid for the approach; interference from a distant station in Dakar led to position uncertainty.
VHF/HF Radio
Used for communication with Robertsfield Tower; contact was intermittent and eventually lost during the descent.
Interesting Facts
- 01The aircraft was a Lockheed L-049 Constellation named 'Clipper Great Republic'.
- 02The aircraft struck the hillside at an elevation of 1,050 feet MSL, approximately 450 feet below the 1,500-foot peak of the hill.
- 03The crash site was located approximately 54 miles northeast of Robertsfield Airport.
- 04The aircraft had approximately eight hours of fuel remaining at the time of the crash.
- 05The investigation found no evidence of mechanical failure or pre-impact fire.
- 06The frequency of the Robertsfield beacon was changed after the accident to prevent further interference from Dakar.
Safety Actions & Advisories
Minimum Altitude Revision
On July 24, 1951, Pan Am raised the minimum instrument approach altitude for Robertsfield to 8,000 feet until further notice.
Operational Restrictions
On August 9, 1951, the CAA restricted Pan Am operations at Robertsfield to VFR (Visual Flight Rules) during daylight hours only.
Frequency Separation
The frequency of the Robertsfield radio beacon was changed to provide greater separation from the Dakar beacon to prevent signal overlap.