LESS THAN STANDARD SEPARATION BETWEEN COMMUTER AND A GA-TWIN. OPERATIONAL ERROR.

Narrative

WE WERE COMMUTER X ON V260 (HPW-RIC). AT ABOUT 4 NM FROM THE RIC VOR WE WERE ISSUED A DSCNT CLRNC TO 8000'. I INITIATED THE DSCNT; BUT THE PNF MISSED THE CALL AND WAS SLOW TO RESPOND. WITHIN 15 SECS THE CTLR RE-ISSUED THE DSCNT CLRNC; ACCOMPANIED BY THE ADVICE THAT 'YOU MIGHT SEE GA TWIN Y AT 11 O'CLOCK; 3 MI AT 9000'.' THE F/O AND I BOTH LOOKED IN THIS DIRECTION BUT SAW NO TFC. JUST PRIOR TO REACHING THE RIC VOR; WHERE WE WOULD TURN NBOUND ONTO V376; WE BOTH SAW THE GA TWIN IN OUR 1 O'CLOCK POS AT APPROX 9000' (WE WERE DSNDING THROUGH 8800' AT THIS TIME) AND A MILE OR LESS AWAY. ACFT Y WAS ALREADY ESTABLISHED ON V376. I CONSIDERED THIS A CLOSE ENCOUNTER AND QUERIED THE RIC APCH CTLR AS TO WHETHER GA ACFT Y WAS ON AN IFR PLAN AND WHETHER HE WAS UNDER THIS CTLR'S GUIDANCE. THE CTLR REPLIED AFFIRMATIVELY TO BOTH QUESTIONS AND APOLOGIZED FOR THE 'LATE CALL.' THIS IS THE FIFTH CLOSE CALL I HAVE HAD IN THE LAST 12 MONTHS; BUT THE FIRST ONE CAUSED BY CTLR ERROR. I DON'T KNOW WHY ACFT Y AND WE WERE BOTH PROGRAMMED TO CROSS RIC AT 9000' AT THE SAME TIME (ACFT Y WAS ALSO ON AN IFR PLAN TO DCA) BUT AT LEAST THE CTLR CAUGHT THE ERROR BEFORE WE WOULD HAVE COLLIDED OVER RIC. THE PLAIN FACT IS THAT IN SOME PARTS OF THE COUNTRY THERE ARE TOO MANY AIRPLANES. SEE AND AVOID IS SIMPLY UNREALISTIC AT THE SPDS OF MODERN ACFT. MANDATORY TCA'S ARE OVERDUE FOR OPS IN BUSY PARTS OF OUR AIRSPACE.