ZTL center controllers reported a loss of separation during a controller switch and briefing.

Attributes
ACN	1449625
Time
Date	201705
Local Time Of Day	1801-2400
Place
Locale Reference	ZTL.ARTCC
State Reference	GA
Environment
Light	Daylight
Aircraft 1
Make Model Name	Large Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Large Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Instructor Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 5
Person 2
Function	Handoff / Assist Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 21
Events
Anomaly	ATC Issue All Types Airspace Violation All Types Conflict Airborne Conflict Deviation - Procedural Clearance Deviation - Procedural FAR Inflight Event / Encounter Weather / Turbulence

Narrative:

I was relieving a controller on R06 with the intent to train an right side trainee. Aircraft landing atl were entering hold and only the far eastern edge of sector was available due to weather. The previous controller issued holding to numerous aircraft on a non-published holding pattern because weather would not allow holding at common fixes. Aircraft X was unable to hold with other aircraft because it was non RNAV. The aircraft were holding where they would need point out to the adjacent sector (37). Before I felt comfortable giving the sector to the trainee; I felt the sector needed to be cleaned up and more orderly. I issued clearances while the trainee updated the data blocks and the relieving controller slide to d-side. I issued aircraft X a descent from FL310 to FL240. I noticed flashing in the vicinity but it was with other aircraft not in my control. Without my noticing the change of two aircraft flashing due to multiple data blocks in the vicinity aircraft X and aircraft Y started flashing. Before I was able to observe and react; aircraft Y stated they were responding to a TCAS at FL290 and climbing. Seconds later aircraft X stated they were responding to a TCAS as well. Make sure the sector is safe and orderly by assuming responsibility.

Original NASA ASRS Text

Title: ZTL Center Controllers reported a loss of separation during a Controller switch and briefing.

Narrative: I was relieving a controller on R06 with the intent to train an R side trainee. Aircraft landing ATL were entering hold and only the far eastern edge of sector was available due to weather. The previous controller issued holding to numerous aircraft on a non-published holding pattern because weather would not allow holding at common fixes. Aircraft X was unable to hold with other aircraft because it was non RNAV. The aircraft were holding where they would need point out to the adjacent sector (37). Before I felt comfortable giving the sector to the trainee; I felt the sector needed to be cleaned up and more orderly. I issued clearances while the trainee updated the data blocks and the relieving controller slide to D-side. I issued Aircraft X a descent from FL310 to FL240. I noticed flashing in the vicinity but it was with other aircraft not in my control. Without my noticing the change of two aircraft flashing due to multiple data blocks in the vicinity Aircraft X and Aircraft Y started flashing. Before I was able to observe and react; Aircraft Y stated they were responding to a TCAS at FL290 and climbing. Seconds later Aircraft X stated they were responding to a TCAS as well. Make sure the sector is safe and orderly by assuming responsibility.

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.