Pan American’s Flight 151 departed Johannesburg for New York. At 08:12, June 21, after a routine flight and scheduled stop at Leopoldville “Clipper Great Republic” arrived at Accra at 21:25. Following a mechanical delay which required the changing of several spark plugs and a set of magneto points, the flight was dispatched and cleared to Monrovia, on an instrument flight plan at 16,500 feet with Dakar. Takeoff from Accra was at 23:52Z and the flight climbed to en route altitude. At 02:20 Flight 151 requested clearance to descend. Roberts Field radio cleared the flight to descend to 3,000 feet. Five minutes later the flight was cleared by the tower controller to descend IFR over Roberts Range Station, and indicated that runway 05 was in use. At 02:37 Flight 151 was again given local weather for Roberts Field: cloud base estimated 1,000 feet, broken, light drizzle and haze, visibility 3 miles. At 02:55, nine minutes after its ETA, Flight 151 was heard calling Roberts Field. The tower responded but there was no indication that the aircraft heard the tower. Six minutes later contact was established on another frequency. The flight reported that the Dakar radio beacon was interfering with the Roberts Field radio beacon and that they would “be back in 15 minutes”. At 03:15 the crew were given another weather report; this was the last radio contact with the flight. In an area where cloud bases were probably down to near the hilltops, the flight descended into a hill at 1050 feet msl and crashed. PROBABLE CAUSE: “The Board determines that the probable cause of this accident was the action of the captain in descending below his en route minimum altitude without positive identification of the flight’s position.”