Was this a plane that encountered a problem during a training maneuver, or simply while standing ready in the air?
Not sure. I know nowadays, training missions don’t ordinarily carry live nukes, not sure about back then, and in this incident. I will look around, online, and see if any more information is available.
From what I just read, in the S.Carolina incident, the plane was flying from Georgia to England, on what was described as an ‘exercise’. The plutonium core was stored, elsewhere, on board, and remained in the plane. The remainder of the bomb fell 15,000 ft., and the detonation of the high explosive trigger created a 50 ft. wide crater, that, today, is a tourist attraction !