ATX X DSCNT THROUGH OCCUPIED ALT WHILE ON RADAR VECTOR HAD LTSS FROM ACFT Y. SYS ERROR.

Narrative

ATX X RECEIVED A CLRNC TO 4000 FT; WITH ASSIGNED HDG 220 DEGS. WHILE DSNDING THROUGH 5000 FT; MY CLRNC WAS AMENDED TO DSND AND MAINTAIN 3000 FT. I WAS THEN ASKED IF I COULD EXPEDITE MY DSCNT. SINCE 500 FPM IS NORMALLY THE MAX DSCNT RATE IN AN UNPRESSURIZED ACFT WITH PAX; I TOLD THE CTLR I WOULD BE UNABLE TO EXPEDITE THE DSCNT. I WAS THEN ASSIGNED A HDG OF 180 DEGS; AND AT THIS POINT WAS PASSING THROUGH APPROX 4300 FT. BEFORE I COULD COMPLETE THIS TURN; I WAS TOLD TO TURN FURTHER L TO A HDG OF 160 DEGS. I WAS THEN INFORMED ACFT Y AT MY 2 O'CLOCK AND 2 MI; SEBOUND; ALT 4000 FT AND WAS TOLD TO EXPEDITE MY DSCNT. SINCE I WAS ALSO APCHING 4000 FT AT THIS TIME; AND SINCE THE TURN PUT THE OTHER ACFT Y IN THE BLIND SPOT UNDER MY WING; I WAS FORCED TO INCREASE TO 1000 FPM DSCNT BRIEFLY TO AVOID THE CONFLICT. THIS SITUATION PROBABLY COULD HAVE BEEN AVOIDED HAD THE APCH CTLR HALTED MY DSCNT TEMPORARILY UNTIL I WAS CLR OF ACFT Y; GIVEN ME AN EARLIER VECTOR TO CLR THE TFC WHILE CONTINUING MY DSCNT; OR INFORMED ME OF THE TFC EARLIER; WHEN I COULD HAVE SEEN IT. I THINK PART OF THE PROBLEM IS ALSO THAT SOME CTLRS ARE NOT AWARE OF OR DO NOT UNDERSTAND PERFORMANCE LIMITATIONS OF UNPRESSURIZED ACFT AND BLIND SPOTS THAT ALL ACFT HAVE.