A320
Air Traffic Control Fully Certified
Communication Breakdown; Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Inflight Event / Encounter Other / Unknown
General None Reported / Taken
Human Factors; Procedure
I was working Air Carrier X into Denver Approach Control and he had been issued a descend via clearance on the Kipper STAR I believe. The descend via clearance had Air Carrier X crossing Landr in the block FL200-220 and continuing his descent as per the STAR after Landr. Approach then called us up and APREQed Citation Jet entering our airspace from approach at FL210; which was landing at SNY an airport inside of my airspace. My D-Side then 'unabled' them because of the traffic and said that FL190 was approved and that we would have Air Carrier X cross Landr at and maintain FL200 at 250 KTS. Everything appeared to be completed. Air Carrier X was shipped to approach and I think that Citation Jet was on my frequency. Both aircraft were inside of approaches airspace. Next thing I know the two aircraft are flashing and Air Carrier X was losing altitude and is directly above Citation Jet. I noticed about a 500 feet vertical separation at its worst point. Not sure what Approach was thinking! This is a rare situation but this is going to be a problem with the new RNAV STAR's and there needs to be some kind of procedure in place. Either Approach needs to take this aircraft out of the departure gate next time or they need to hand the SNY arrival off to Denver Center Sector 15 at or below the altitude restriction for the first fix inside of Approaches airspace.
ZDV Controller described a conflict involving traffic handed off to Denver TRACON and traffic entering his/her sector; noting the separation instructions were forwarded but apparently not followed.