What was found
(CAN) ON ARRIVAL INTO THE NR 1 AHRS TOPPLED AND LOST THE FLIGHT DIRECTOR. FAULTY AHRS PN:7003360-941, SN: 88071070. REPLACED AND GROUND CHECKS CARRIED OUT AND CHECKED SERVICEABLE. ACFT RETURNED TO SERVICE. ON THE CLIMBOUT RT AFTER REPLACING THE AHRS, NR 1 AHRS TOPPLED IN FLIGHT. THE ACFT RETURNED TO DEPARTURE AND ONCE AGAIN REPLACED THE NR 1 AHRS, PN: 7003360-941, SN: 90091836. GROUND CHECKS CARRIED OUT, CHECKED SERVICEABLE. THE UNIT THAT WAS INSTALLED THE FIRST TIME HAD BEEN PREVIOUSLY REMOVED FOR A FAILURE AND HAD BEEN SENT TO MFG FOR REPAIR. IT HAS BEEN BACK HERE FOR AWHILE NOW SITTING IN STOCK UNTIL WE REQUIRED ITS USE. THESE UNITS ARE USUALLY A HIGH USAGE ITEM FOR US AND CONTINUE TO BE IN THE TOP TEN WORLD FLEET FLIGHT INTERRUPTION DRIVERS. TYPICALLY THEY AVERAGE ABOUT 2 YEARS BETWEEN FAILURE FOR US BUT WE HAVE SEEN A NR OF THESE FAIL, OFF THE SHELF WHEN THEY COME BACK FROM THE MFG. THE MFG IS THE ONLY AUTHORIZED REPAIR STATION FOR THESE UNITS.