Enroute controller described a loss of separation event during holding procedures when an aircraft e...

Narrative:

I assumed my sector; which already had a d-side staffed in the hand off position due to equipment issues. I was briefed that a major airport was shut off due to weather and we were already holding. The supervisor made the outgoing r-side relieve the existing d-side to remain and help. We were told we would be holding for about an hour or so. I believe we had between 5 and 7 aircraft in holding along with some overflights. The numbers grew fairly quickly within what seemed like minutes. I accepted the closed airport arrival hand offs from the neighboring center; along with multiple overflights from other sectors. Frequency congestion became a factor as aircraft began inquiring about the delay and alternates. My d-side did a great job coordinating altitudes with adjacent sectors. As aircraft would check on; I would evaluate if they were a factor for my holding stacks. This seemed to be working. When an A320 checked on; it took a few more seconds than usual to locate him. When I did; he was already within the lateral confines of my holding stack at the intersection. As I noticed this; I quickly scanned for traffic. I concluded that he was okay. It seemed like only minutes went by when the controller on the adjacent sector commented; at the same time I saw it. Within seconds; and as I began turning both aircraft; the conflict alert went off. Not more than seconds after I issued vectors; both aircraft responded to TCAS. I stopped issuing any instructions after that and told both aircraft to let me know when they were done responding. After they were separated; the A320 was cleared direct to the VOR; and the MD80 was eventually put back in holding. I don't know if there is anything outside of my own self evaluation of how I scanned my overflights that could have helped. This was my error. I wasn't able to scan my overflights until they checked in. I should have seen; if some one's check in was delayed; so would their traffic search [be delayed]. I don't think there were any bad procedures; plans or configurations in place.

Original NASA ASRS Text

Title: Enroute Controller described a loss of separation event during holding procedures when an aircraft entered the holding pattern at an occupied altitude shortly after hand off; listing only a lack of vigilance as a causal factor.

Narrative: I assumed my sector; which already had a D-Side staffed in the hand off position due to equipment issues. I was briefed that a major airport was shut off due to weather and we were already holding. The Supervisor made the outgoing R-Side relieve the existing D-Side to remain and help. We were told we would be holding for about an hour or so. I believe we had between 5 and 7 aircraft in holding along with some overflights. The numbers grew fairly quickly within what seemed like minutes. I accepted the closed airport arrival hand offs from the neighboring Center; along with multiple overflights from other sectors. Frequency congestion became a factor as aircraft began inquiring about the delay and alternates. My D-Side did a great job coordinating altitudes with adjacent sectors. As aircraft would check on; I would evaluate if they were a factor for my holding stacks. This seemed to be working. When an A320 checked on; it took a few more seconds than usual to locate him. When I did; he was already within the lateral confines of my holding stack at the intersection. As I noticed this; I quickly scanned for traffic. I concluded that he was okay. It seemed like only minutes went by when the controller on the adjacent sector commented; at the same time I saw it. Within seconds; and as I began turning both aircraft; the Conflict Alert went off. Not more than seconds after I issued vectors; both aircraft responded to TCAS. I stopped issuing any instructions after that and told both aircraft to let me know when they were done responding. After they were separated; the A320 was cleared direct to the VOR; and the MD80 was eventually put back in holding. I don't know if there is anything outside of my own self evaluation of how I scanned my overflights that could have helped. This was my error. I wasn't able to scan my overflights until they checked in. I should have seen; if some one's check in was delayed; so would their traffic search [be delayed]. I don't think there were any bad procedures; plans or configurations in place.

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.

Attributes
ACN	955336
Time
Date	201106
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Aircraft 1
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
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
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Published Material / Policy

Enroute controller described a loss of separation event during holding procedures when an aircraft entered the holding pattern at an occupied altitude shortly after hand off; listing only a lack of vigilance as a causal factor.