What was found
AIR TURN BACK: F/OS AIR SPEED INDICATOR STOPPED AT 138 KTS. MACH OK. ALL OTHER FLIGHT INDICATONS OK. SWITCHED TO ALTERNATE STATIC-NO HELP. RETURNED TO ORD. C/A: REPLACED F/OS AIR SPEED INDICATOR AND ACCOMPLISHED FULL PITOT STATIC CHECK WITH 500 TESTER. CHECKS OK PER MM. MAINTENANCE ALSO ACCOMPLISHED CONDITIONAL OVER WEIGHT LANDING INSPECTION PER MM. NO DISCREPANCIED NOTED.