Pan Am Flight 151

The Johannesburg to New York City flight was on the Accra, Gold Coast (now Ghana), to Monrovia, Liberia leg of its journey. At 0301h during a pre-dawn approach to Monrovia's Robertsfield Airport, the flight crew reported to the tower that the radio beacon at Dakar, Senegal was interfering with the Robertsfield radio beacon.[2] After a 0315h weather report was sent to the pilots, all contact with the aircraft was lost. The flight was reported missing at 0410h on June 22, and an aerial search was conducted, but it was unsuccessful in locating the aircraft. At 1430h on June 23, a foot messenger arrived from the village of Sanoyie to report that an aircraft crashed into the side of a hill one day earlier several miles from the village and that everyone aboard was killed.

After a day's search, the "completely disintegrated remains of the Pan American World Airways plane that disappeared over West Africa Thursday night were found yesterday," Harold R. Harris, vice president of the line said. Searchers from a Lutheran mission at Sanoye, Liberia, first located the shattered four-engine plane that had carried thirty-one passengers and a crew of nine. Later, Pan American officials in a company plane flew over the wreckage and identified it.

What was left of the big transport was found by the mission hunting party about four miles southwest of the village of Sanoye and about 45 miles north-northeast of Roberts Field. The plane had hit near the top of a 1,500-foot hill.

— The New York Times, June 24, 1951

It was determined that the location where the flight crashed was beyond the effective range of the Robertsfield beacon.[2] This, combined with the report from the crew that the Dakar beacon was interfering with the Robertsfield beacon, resulted in the frequency of the Robertsfield beacon being changed to provide greater separation of frequencies between the two beacons.[2] Investigation of the wreckage revealed no indications of mechanical malfunction, the aircraft had enough fuel for another eight hours of flight, the weight and disposition of the payload was within allowable limits, and the weather was above minima.

The Civil Aeronautics Board investigation concluded that the probable cause of the accident was the action of the captain in descending below his en route minimum altitude without positive identification of the flight's position.[2]

• Accident description at the Aviation Safety Network