What was found
AIRCRAFT WAS GROUNDED: DURING CRUISE AT FL370 WITH AP A ENGAGED, IRS NR 1 FAULT. THIS RESULTED IN THE LOSS OF CA PFD, BOTH AUTOPILOTS, AUTOTHROTTLE FAIL, YD FAIL AND SPEED TRIM SYSTEM FAIL. AFTER STABILIZING THE AIRCRAFT, TRIED TO RE-ENGAGE AP'S BUT WERE UNSUCCESSFUL. YD WOULDNOT REENGAGE. SPEED TRIM SYSTEM FAIL, AUTOTHROTTTLE FAILED. ALL QRH'S REFERENCED IN REGARDS TO THE FAILED SYSTEMS LISTED ABOVE. AN EMERGENCY WAS DECLARED, LANDED NORMALLY AND TAXIED TO THE GATE. MAINTENANCE T/S CONFIRMED #1 IRU FAULTING. REPLACED #1 AIR DATA INERTIAL REFERENCE UNIT IAW MM 34-21-01. ALL TESTS PASSED. PERFORMED LAND VERIFY AND HUD TEST. ALL TESTS PASSED. ALL INBOUND FLT FAULTS ON DFCS WERE RELATED TO #1 IRS FAILURE.