What was found
FLT NR 6523 - IAD-PWM - DURING CRUISE RETURNED TO IAD DUE TO THE AUTOPILOT FAILING AND MODE C INOP. AIRCRAFT LANDED WITH NO FURTHER INCIDENTS. MAINTENANCE SELECTED ATC WINDOW TO READ ATC ALTITUDE. PERFORMED TRANSPONDER CHECKS, OPS CHECKS GOOD. OPENED DMI NR 20959 IAW MEL 22-1 ON 4-21-95. MAINTENANCE LATER CLEARED DMI NR 20959 ON 2-24-95 BY REPLACING THE FLIGHT CONTROL COMPUTER. AIRCRAFT WAS RELEASED AND APPROVED FOR RETURN TO SERVICE. (W)