What was found
FLT#479, JFK-MBJ. (AIRCRAFT PERFORMED AN AIR TURN BACK AND DECLARED AN EMERGENCY) ' NAV 1 ADR FAULT 1 DURING FLIGHT. MADE AN EMERGENCY RETURN AND ACCOMPLISHED AN OVERWEIGHT LANDING. LANDING WEIGHT 157,000 TOUCH DOWN 250-300 FEET PER MIN. NO OVERSPEED. SMOOTH TOUCHDOWN; REF LOG PAGE 3845703 FOR CORRECTIVE ACTION . AC OKAY FOR SVC. REF TSM 34-53-31, UNABLE TO REPLICATE FAULT, REMOVED AND REPLACED ADIRU 1 AS A PRECAULTIONARY/T/SHOOTING IAW AMM TASK 34-12-34. BITE TEST ADR IAW AMM TASK 34-00-00 AND TEST IR IAW AMM TASK 34-14-00, ALL OPS CHECK NORMAL'