CPR Y HAD LESS THAN STANDARD SEPARATION DURING DSCNT FROM SMT X. SYS ERROR. CPR Y DSCNT THROUGH ASSIGNED ALT. PLTDEV.

Narrative

SMT X WAS ON FREQ DSNDING TO FL180. CPR Y; CHKED ON DSNDING TO FL280. I OBSERVED SMT X LEAVING FL270; AND ISSUED A DSCNT CLRNC TO FL270 TO CPR Y. SINCE SMT X WAS DSNDING AT A SLOWER RATE THAN THE TFC ABOVE; I AMENDED HIS DSCNT CLRNC TO INCLUDE A MIN RATE OF DSCNT OF AT LEAST 1000 FPM UNTIL HE DEPARTED FL260. THIS CLRNC WAS ACCEPTED; WITH A QUESTION; BY CPR Y; WHO RESPONDED AS USE OF AN INCOMPLETE (AND INCONSISTENT) CALL SIGN. THE ACKNOWLEDGEMENT OF THE CLARIFIED INSTRUCTION WAS ACCOMPLISHED WITHOUT A CALLSIGN. I NOTICED CPR Y DSNDING THROUGH FL270 AND ASKED HIM TO VERIFY LEVEL. WHEN HE RESPONDED THAT HE WAS GOING THROUGH FL260; I INSTRUCTED HIM TO 'STOP DSCNT'; THIS WAS TO PRESERVE ANY VERT SEPARATION THAT I STILL HAD. I THEN REASSIGNED FL260 TO CPR Y AND INSURED THAT SMT X WAS UNDER THAT ALT. I FEEL THAT THE FOLLOWING FACTORS WERE CONTRIBUTORY TO THE INCIDENT: USE OF INCOMPLETE CALL SIGNS BY THE PLT AND MYSELF. NO CALL SIGN USED ON FINAL AMENDED CLRNC AND ACKNOWLEDGEMENT. CALL SIGN GIVEN OUT OF ORDER DURING THE MIDDLE OF A READBACK QUESTION. STAFFING AT THE FACILITY WAS SHORT ENOUGH TO PREVENT A RADAR ASSOCIATE BEING USED.