What was found
AUTOPILOT "A" BEGAN OSCILLATING UP AND DOWN 30' AT CRUISE. FL360 SAT-53C 265 KTS .798 MACH. TRIM WHEEL MOVED CONTINUOUSLY FORWARD AND AFT. SELECTED AUTOPILOT B AND OSCILLATING STOPPED. RE-SELECTED AUTOPILOT A AND OSCILLATIONS CONTINUED. SWITCHED BACK TO AUTOPILOT B AND NO OSCILLATIONS. ACFT GROUNDED. CONFIRMED DEFECT, STABILIZER TRIM SENSOR A READS 0.00 VAC AT ALL STAB POSITIONS. R AND R STABILIZER POSITION SENSOR A IAW AMM 22-11-31-000-801, 22-11-31-400-801. PERFORMED STABILIZER POSITION SENSOR ADJUSTMENT IAW AMM 22-11-31-820-801 AND DFCS GROUP 44, STAB SENSOR LRU REPLACEMENT, TEST IAW AMM 22-11-31-710-801. ALL TESTS PASSED. PERFORMED FULL DFCS GROUP NR 60, BITE LIBRARY TEST, IAW AMM 22-11-00-740-806, DFCS GROUP NR 49, LAND VERIFY, TEST IAW AMM 22-11-00-700-801, AUTOTHROTTLE OPS TEST IAW AMM 22-31-00-710-801, AND HGS SYSTEM TEST IAW HGS AMM 34-36-00. ALL TESTS PASSED. ACFT IS QUALIFIED FOR CAT IIIA AUTOLAND AND HGS OPS AND STATUS PLACARD REFLECTS SAME.