 Several of the aircraft had experienced runaway propellers, a situation where the pilots were unable to control the pitch of the propellers and centrifugal force causes the blades to adjust to the lowest pitch, leading to aerodynamic instability.In 1952, Pan Am Flight 202 crashed in the Amazon Basin after its engine and propeller failed in flight.In 1955, Pan Am Flight 845/26 ditched in the Pacific Ocean off the coast of Oregon with four fatalities after one of the aircraft's propellers failed and caused the engine to separate from the wing.