FLC OF MLG FAILED TO REDUCE SPD PER ATC CTLR INSTRUCTIONS DUE TO THE FACT THAT THEY WERE UNABLE TO EXTEND MORE FLAPS AT THAT MOMENT.

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ON ILS 32 APCH INTO PIT APCH CTL WAS BUSY WITH NUMEROUS ACFT INBOUND AND WE WERE SEQUENCED BEHIND; I BELIEVE IT WAS A BEECH 1900 AND WERE INSTRUCTED TO SLOW TO 210 KTS; 190 KTS AND LATER 160 KTS AT MARKER. AT THAT TIME WE EXTENDED FLAPS AND GEAR TO SLOW OUR MANEUVERING SPD AND FLAPS WOULD NOT EXTEND BEYOND FLAPS 5. AT OUR LNDG WT WE COULD NOT SLOW TO ASSIGNED SPD. WHILE CAPT WAS CHKING CIRCUIT BREAKERS I WAS TRYING TO CALL APCH CTL (ABOUT 3 CALLS WERE BLOCKED BY OTHER ACFT). A DIFFERENT CTLR CAME ON (SUPVR?) AND GAVE TURN CLB AND CANCELED APCH CLRNC. AND AT THAT TIME I ADVISED HIM WE HAD A FLAP PROB AND REQUESTED A VECTOR TO SW OF ARPT BECAUSE TCASII DID NOT SHOW ANY OTHER TFC IN THAT AREA. AT FIRST HE WAS GOING TO GIVE US A HOLD AT AGC VOR BUT WE TOLD HIM ALL WE NEEDED WAS A VECTOR OUT FOR ILS 28 AND 15-20 MI FINAL. WE COMPLETED ALL CHKLISTS AND LANDED WITHOUT INCIDENT. HE ASKED IF WE NEEDED CRASH/FIRE/RESCUE AND WE DECLINED. THEY NEEDED SOB AND FUEL FOR THEIR RPTS. REST OF FLT WAS NORMAL EXCEPT FOR FLAP PROB.