What was found
MAN FLT 735 EN ROUTE MAN TO PHL. THE FLIGHT HAD AN ADIRU 3 FAILURE PRIOR TO ETOPS AIRSPACE, PREVENTING ETOPS OPERATIONS. THE FLIGHT RETURNED TO FIELD MAN, AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE SWAPPED ADIRU 3 WITH ADIRU 2, AND PLACED ADIRU 2 ON MEL. MAINTENANCE REPLACED ADIRU 2. OPERATIONAL CHECKS OK. (S)