ZDV controller reports of a loss of separation due to a slow descent rate of the lower aircraft.

Narrative:

The southwest arrival gate was shut-off due to weather. Their arrivals were routed tower-en-route via publication..brk..fqf..kden. This took all the southwest arrivals head-on with all the south departures (as they were coming out via spazz/stakr/publication due to weather). Towards the tail end of the arrival push; aircraft X was approximately 5 miles in front of aircraft Y a apa arrival deviating. R2601 was active FL349 and below complicating matters. After aircraft Y was no longer deviating north (toward R2601); I assigned present heading. At this time; both aircraft X and aircraft Y were descending 170. Aircraft X had been a few thousand feet lower the entire time. I turned aircraft X direct brk thinking aircraft Y would stay behind still. I slowed aircraft Y to 250kt. The turn to brk was enough to where I was going to loose lateral separation. At this time; aircraft Y was descending through FL230 and aircraft X was leaving FL220. I stopped aircraft Y at FL220; and expedited aircraft X to 170. I believe aircraft X did not descend at a rate quickly enough to keep separation. I noticed while aircraft Y was on the edge of the bubble; aircraft X was leaving FL212 and aircraft Y was leveling off at FL220. There was also an ALS arrival; and an ALS departure while all of this was going on. I should have used vertical separation until I was sure lateral would work.

Original NASA ASRS Text

Title: ZDV Controller reports of a loss of separation due to a slow descent rate of the lower aircraft.

Narrative: The southwest arrival gate was shut-off due to weather. Their arrivals were routed tower-en-route via PUB..BRK..FQF..KDEN. This took all the southwest arrivals head-on with all the south departures (as they were coming out via SPAZZ/STAKR/PUB due to weather). Towards the tail end of the arrival push; Aircraft X was approximately 5 miles in front of Aircraft Y a APA arrival deviating. R2601 was active FL349 and below complicating matters. After Aircraft Y was no longer deviating north (toward R2601); I assigned present heading. At this time; both Aircraft X and Aircraft Y were descending 170. Aircraft X had been a few thousand feet lower the entire time. I turned Aircraft X direct BRK thinking Aircraft Y would stay behind still. I slowed Aircraft Y to 250kt. The turn to BRK was enough to where I was going to loose lateral separation. At this time; Aircraft Y was descending through FL230 and Aircraft X was leaving FL220. I stopped Aircraft Y at FL220; and expedited Aircraft X to 170. I believe Aircraft X did not descend at a rate quickly enough to keep separation. I noticed while Aircraft Y was on the edge of the bubble; Aircraft X was leaving FL212 and Aircraft Y was leveling off at FL220. There was also an ALS arrival; and an ALS departure while all of this was going on. I should have used vertical separation until I was sure lateral would work.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1198237
Time
Date	201408
Local Time Of Day	1801-2400
Place
Locale Reference	DEN.Airport
State Reference	CO
Environment
Light	Night
Aircraft 1
Make Model Name	Large Transport
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Aircraft 2
Make Model Name	Light Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 1.5
Events
Anomaly	Conflict Airborne Conflict Deviation - Procedural Published Material / Policy Inflight Event / Encounter Weather / Turbulence