What was found
SEA - "ELEVATOR FEEL" MASTER CAUTION OBSERVED DURING CLIMB ATTITUDE AND HEADING REFERENCE INFO LOST ON NR 1 SIDE. SWITCHING TO NR 2 AHRS RESTORED ATT/HDG TO NR 1 SIDE. RETURNED THE FILED AND ACCOMPLISHED A UNEVENTFUL LANDING. AIRCRAFT LANDED BELOW MAX LANDING WEIGHT. REMOVED AND REPLACED NR 1 AHRS IAW MTC 6342101. OPS TEST IS GOOD. ALL ATTITUDE AND HEADING INDICATIONS ARE NORMAL ON THE NR 1 SYSTEM. NO CAUTIONS NOTED. A/C REMAINS CAT III PLACARDS STATES CAT III STATUS. RETURNED TO SERVICE.