ZAU controller described a loss of separation event when he/she descended an aircraft to an occupied...

Attributes
ACN	920590
Time
Date	201011
Local Time Of Day	0001-0600
Place
Locale Reference	ZAU.ARTCC
State Reference	IL
Aircraft 1
Make Model Name	A319
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Aircraft 2
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Person 2
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 225 Flight Crew Total 15000 Flight Crew Type 7300
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Published Material / Policy

Narrative:

An A320 was direct eck at FL350 soon to exit my sector. An A319 was at FL360 inbound to mke. The sector was fairly busy as was sector 25. I was distracted by sector 25 sequencing dtw inbounds still at FL330 in my airspace; but I was not talking to any of those aircraft because there is a flash-through procedure. For whatever reason; I descended the A319 to FL340 right in the face of the A320. The A320 told me that he was descending as the conflict alert went off. He started to descend to FL340 but the two aircraft were soon clear. I told the A320 to climb back up to FL350; and I believe he only descended a few hundred feet. I then shipped him to cleveland center. I told the A319 to descend to FL340 again.

Original NASA ASRS Text

Title: ZAU Controller described a loss of separation event when he/she descended an aircraft to an occupied altitude; distracted by other sector activities.

Narrative: An A320 was direct ECK at FL350 soon to exit my sector. An A319 was at FL360 inbound to MKE. The sector was fairly busy as was Sector 25. I was distracted by Sector 25 sequencing DTW inbounds still at FL330 in my airspace; but I was not talking to any of those aircraft because there is a flash-through procedure. For whatever reason; I descended the A319 to FL340 right in the face of the A320. The A320 told me that he was descending as the Conflict Alert went off. He started to descend to FL340 but the two aircraft were soon clear. I told the A320 to climb back up to FL350; and I believe he only descended a few hundred feet. I then shipped him to Cleveland Center. I told the A319 to descend to FL340 again.

Data retrieved from NASA's ASRS site as of April 2012 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.

ZAU controller described a loss of separation event when he/she descended an aircraft to an occupied altitude; distracted by other sector activities.