What was found
DURING DESCENT, WHEN ENGAGING LEVEL CHANGE MCP SPEED WOULD CHANGE TO RANDOM UNWANTED, UNSPECIFIED SPEEDS REGARDLESS OF DESIRED DESCENT SPEED. ADDITIONALLY, A/C DID NOT HONOR THAT SPEED. AUTOPILOT IGNORED THESE RANDOM SPEEDS AND WOULD NOT CHANGE A/C ATTITUDE TO ATTAIN THE SPEED IN THE MCP IAS WINDOW. GROUNDED - YES. ACCOMPLISHED B737-800 FIM TASK 22-11-00-810-801 - DIGITAL FLIGHT CONTROL SYSTEM (DFCS) BITE PROCEDURE. NO CURRENT FAULTS FOUND. THERE WERE SEVERAL FAULTS MESSAGES 22-11822. NO LEVEL CHANGE FAULTS NOTED. ACCOMPLISHED BOTH FMCS LRU REPLACEMENT TESTS, REF B737-800 FIM 22-11 TASK 802. NO FAULTS FOUND. PRECAUTIONARILY REPLACED MCP PANEL. REMOVED AND INSTALLED NEW MCP PANEL, REF B737-800 AMM TASK 22-11-34-400-801. PERFORMED MODE CONTROL PANEL INSTALLATION TEST, REF B737-800 AMM TASK 22-11-34-740-801. SYSTEM CHECKS NORMAL PER LWMP SYSTEM COMPONENT TABLE. PERFORMED DFCS LRU INTERFACE TEST FOR MCP, REF B737-800 AMM 22-11-00/201. GROUP 32, LAND VERIFY, REF B737-800 AMM 22-11-00/201. GROUP 49 AND HGS SENSOR TESTS FOR FCC/AT, REF SMM 34-36-00. ALL TESTS PASSED. AIRCRAFT IS UPGRADED TO CAT IIIA AUTOLAND AND HGS QUALIFIED. STATUS SCREW MOVED TO REFLECTS SAME.