Date: 201304
Local time of day: 1201-1800
Location: ZDV.ARTCC, CO
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class A ZDV
ATC / advisory: Center ZDV
Second aircraft: Dash 8 Series Undifferentiated or Other Model
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Second reporter function: Enroute
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
Result: General None Reported / Taken
Contributing factors: Procedure; Human Factors
Primary problem: Procedure

Narrative: I was training on the 13 D-Side. A Dash 8 was descending out of FL190 to cross TOMSN at 17;000 and 250 KTS on the TOMSN6 star into DEN. A B737 was direct TOMSN on the FRNCH1 RNAV STAR into DEN. The B737 was originally stopped at FL230 for overflight traffic. When the B737 cleared the overflight traffic he was given a descend via the FRNCH1 STAR into DEN. The Dash 8 was leveling at 17;000 underneath the B737 at the time. I advised 13 RADAR of the Dash 8 traffic. The 13 RADAR Controller then shipped the B737 to DEN Approach and told the B737 to advise them he was 'descending via'. In my view the 13 RADAR Controller was counting on DEN Approach Controller having enough time to initiate some form of separation. About a minute after both aircraft passed TOMSN; the DEN Approach Controller called over the land line and said he wasn't talking to either aircraft. Then again over the land line the Approach Controller said never mind. I told the 13 RADAR Controller to try them both again anyway. The Dash 8 was still on our frequency. I don't know if he got shipped to DEN Approach and didn't change frequency or did not get shipped at all. With both aircraft checking in late with DEN Approach there was no time for the DEN Approach Controller to save the loss of separation. There are procedures in place via LOA between DEN Center and DEN Approach to stop jet aircraft on RNAV STARs at the lowest altitudes available in the block restrictions at the 'gate fix' on the RNAV STAR when there is traffic below them over the same fix. In this instance this was not done. In general I think that the procedures in place for RNAV STARS into DEN Approach are not safe; given there is no positive separation with the possible converging of the old 'Legacy STARs' and the new RNAV STARS. To accommodate for the loss of positive separation the DEN Approach LOA states that the arrivals shall be shipped five miles from the gate fixes which is inside DEN Centers boundaries. The thinking behind it that the approach controller can initiate separation before it becomes a loss of separation. The legacy stars are mostly used for prop aircraft. This is especially true when you are landing via the short side RNAV STARs at DEN Approach from the southwest side. This is not where this event happened but I think it much more likely to be able to happen again there even following the LOA procedures. These procedures seem to go against what I have learned about positive separation since becoming a controller. Personally; I stop the RNAV arrivals on top of the props on either side of the parallel arrivals into DEN Approach; but most do not; and I am told you are not required to do so. I think these procedures led the 13 RADAR Controller in this event to think that there was no real difference in this situation in giving up positive separation.


Second narrative: [Narrative 2 contained no additional information.]


Synopsis: A ZDV Controller described a loss of separation when traffic inbound to D01; one via a new RNAV STAR and another on a 'Legacy' STAR conflicted.