To be fair to Pan Am and Dan Air, IIRC the corrosion was in the tail area and it had not been realised by any of the airworthiness authorities or operators that this was a weak spot. I can't remember whether the aircraft had IAS on the tail or the fuselage and I worked for IAS! I was in the office the morning BP crashed (we were notified by telex and I can still remember the scream from the telex operator as she read it).