DISTR BY MALFUNCTIONING FLT MGMNT GUIDANCE SYS; FLT CREW OF MD80 ELECTS TO SLOW ACFT BELOW ASSIGNED AIRSPD TO MITIGATE WORKLOAD. FOLLOWING ACFT TOLD TO GO AROUND DUE TO INADEQUATE SPACING.

Narrative

SHORTLY AFTER LOC CAPTURE/LOC TRACK; THE HEADING CURSOR ON THE FO'S HSI DRIFTED OFF SELECTED HEADING BY APPROX 30-45 DEGS TO THE R. THE HEADING SELECT KNOB WOULD NOT DRIVE THE HEADING CURSOR ON THE FO'S HSI. FO DISCONNECTED THE AUTOPLT AND THE APCH WAS FLOWN MANUALLY. THESE EVENTS OCCURRED A COUPLE OF MI OUTSIDE OF TAPPS OM. ATC HAD ASSIGNED AN AIRSPD OF 180 KTS OR BETTER TO THE MARKER. GIVEN OUR SIT I THOUGHT IT PRUDENT TO SLOW TO FINAL APCH SPD AND CONFIGURE AS WE REJOINED THE LOC/GS. UNFORTUNATELY FOR THE ACFT IN TRAIL THEY WERE INSTRUCTED TO GO AROUND BY THE TWR. AFTER CLRING THE RWY TWR GAVE US A LCL PHONE NUMBER FOR ORD TRACON. (NEVER A GOOD SIGN.) I SPOKE WITH A CTLR WHO WANTED TO KNOW WHY WE SLOWED EARLY AND WERE NOT ABLE TO MAINTAIN OUR ASSIGNED AIRSPD. I EXPLAINED WE EXPERIENCED A SYS MALFUNCTION AND IN THE PROCESS OF FLYING THE AIRPLANE; LIMITED TROUBLESHOOTING; CHKLIST COMPLETION AND FREQ CONGESTION I WAS NOT ABLE TO GIVE THEM A CALL. HE UNDERSTOOD. I ASKED HIM IF HE WOULD PURSUE THIS MATTER FURTHER AND HE SAID NO.