INADEQUATE DESIGN OF THE AIRSHIP, WHICH ALLOWED THE CENTER BALLONET TO OVERFILL AND TO COLLAPSE THE TRUNKING TO THE FORE AND AFT BALLONETS, RENDERING THE AIRSHIP UNCONTROLLABLE. FACTORS RELATED TO THE ACCIDENT WERE: INADEQUATE MAINTENANCE BY THE COMPANY/OPERATOR, WHICH ALLOWED THE PURITY OF THE HELIUM TO DECREASE; AND THE CENTER DAMPER VALVE TO OPEN (OR TO BE LEFT OPEN FOR FLIGHT).