B777 CREW HAD AUTOFLT AND AUTOTHROTTLE ANOMALIES IN EGCC CLASS B AIRSPACE.

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THE EVENT DID/DOES NOT INVOLVE ANY ACFT/ATC VIOLATION. THE SCENARIO IS RELATED SOLELY FOR ADVISORY OF FMC MALFUNCTION. FINAL APCH TO RWY 6L; MAN; UK; CLRED TO DSND FROM FL090 TO 4000 FT. FLT LEVEL CHANGE SELECTED ON AUTOPLT; FO FLYING. AT +-4500 FT; CAPT AND FO SET LCL ALTIMETER OF 1025 HECTOPASCALS. ATC ISSUED SPD REDUCTION TO 210 KTS; FLAPS 1 DEG SELECTED. 'SPD' AND 'FLT LEVEL CHANGE' ANNUNCIATION ON FMA. A YELLOW BOX APPEARED AROUND FO AND CAPT ALTIMETER INDICATING WINDOW AND ACFT LEVELED OFF AT 4150 FT. CREW THEN NOTED 'ALT HOLD' BUTTON ILLUMINATED. FO RESELECTED FLT LEVEL CHANGE; ACFT STILL DID NOT DSND TO 4000 FT. AT THIS TIME BOTH CAPT AND FO OBSERVED AIRSPD DECELERATE BELOW 190 KTS; AUTOTHROTTLE ENGAGED; SPD IN MCP SET TO 210 KTS; FLT LEVEL CHANGE SELECTED. ATC WAS VECTORING TOWARD LOC INTERCEPT AND REQUESTED 'RPT ESTABLISHED.' FO ADDED PWR; REQUESTED 'FLAPS 5 DEGS' AND ANNOUNCED 'AUTOPLT COMING OFF.' ACFT WAS HAND FLOWN DOWN TO 4000 FT AND ACCELERATED TO 210 KTS. YELLOW BOX AROUND ALTIMETER INDICATOR WINDOW DISAPPEARED AND AFTER APPROX 60 SECONDS; AUTOPLT RE-ENGAGED (SELECTED) AND ACFT RESUMED NORMAL SPD AND ALT (GS TRACKING) CTL. LESS ATTN TO SITUATIONAL AWARENESS OR AN INCREASED DISTR LEVEL COULD HAVE RESULTED IN A MISHAP.