Narrative:

I took over the position from another controller. A B737 was a hobby departure climbing northbound and I was briefed he was climbing to his requested altitude of FL390. At some point I thought I switched the B737 to ZFW paxto sector who had the hand off so I had slant zeroed the data block. After reviewing the tape it appears I did not ever issue a frequency change. I took the hand off on a LR45 a few minutes later and he checked on. A few minutes more and the conflict alert activated on the B737 and the LR45. I even joked to the guy next to me working low altitude that I hoped paxto had stopped that B737 at 370 but I didn't call as false alerts are very; very common between our two sectors because of LOA procedures and complexity. It's not unusual for ZFW to take the hand off on traffic that will be in conflict with traffic in their airspace without issuing a restriction and just take care of it themselves. I assumed that was the case here as well. I suppressed the ca and dropped the data block on the B737 as he was leaving my airspace. A little bit later paxto called me on the shout line and said something like 'I assume the B737 is stopped at FL370?' my response was 'who?' then I realized who they were probably talking about and I brought up the data block again. The B737 was about 15 miles in front of the LR45 head on climbing through FL363. I said 'no he was climbing to FL390'. The paxto controller then said 'well we're not talking to him.' I quickly punched off the line and radioed the B737. He answered. I told him to amend altitude maintain FL370 and then issued a traffic alert. He said he was probably going to go through it but he would go back down. They never went about FL371 and leveled in time to maintain separation. While I still think it's impractical to always call another controller to make sure a potential conflict is taken care of; it's very dangerous to assume and if there is any doubt at all I should make sure it's been handled. At the very least I could have checked just to make sure the B737 was not on my frequency and then would have discovered he was and was therefore still climbing into the traffic. Paxto called me because they weren't talking to the B737; 15 miles into their airspace; and climbing head-on into traffic. The very first thing they should have told me was they weren't talking to him and stop him at 370; not passively saying they assumed he was stopped at 370! I was probably not as focused as I should have been which is how I mistakenly thought I had switched the B737. I might have slant zeroed his data block by accident while issuing a frequency change to another aircraft. I clearly remembered switching the B737 and getting an acknowledgment until I listened to the tape!

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Original NASA ASRS Text

Title: ZHU Controller described a near loss of separation event when failing to note an aircraft was not frequency transferred to the receiving controller as a conflict was developing.

Narrative: I took over the position from another Controller. A B737 was a Hobby departure climbing northbound and I was briefed he was climbing to his requested altitude of FL390. At some point I thought I switched the B737 to ZFW PAXTO Sector who had the hand off so I had slant zeroed the data block. After reviewing the tape it appears I did not ever issue a frequency change. I took the hand off on a LR45 a few minutes later and he checked on. A few minutes more and the Conflict Alert activated on the B737 and the LR45. I even joked to the guy next to me working low altitude that I hoped PAXTO had stopped that B737 at 370 but I didn't call as false alerts are very; very common between our two sectors because of LOA procedures and complexity. It's not unusual for ZFW to take the hand off on traffic that will be in conflict with traffic in their airspace without issuing a restriction and just take care of it themselves. I assumed that was the case here as well. I suppressed the CA and dropped the Data Block on the B737 as he was leaving my airspace. A little bit later PAXTO called me on the shout line and said something like 'I assume the B737 is stopped at FL370?' My response was 'Who?' Then I realized who they were probably talking about and I brought up the data block again. The B737 was about 15 miles in front of the LR45 head on climbing through FL363. I said 'No he was climbing to FL390'. The PAXTO Controller then said 'Well we're not talking to him.' I quickly punched off the line and radioed the B737. He answered. I told him to amend altitude maintain FL370 and then issued a traffic alert. He said he was probably going to go through it but he would go back down. They never went about FL371 and leveled in time to maintain separation. While I still think it's impractical to always call another controller to make sure a potential conflict is taken care of; it's very dangerous to assume and if there is any doubt at all I should make sure it's been handled. At the very least I could have checked just to make sure the B737 was not on my frequency and then would have discovered he was and was therefore still climbing into the traffic. PAXTO called me because they weren't talking to the B737; 15 miles into their airspace; and climbing head-on into traffic. The very first thing they should have told me was they weren't talking to him and stop him at 370; not passively saying they assumed he was stopped at 370! I was probably not as focused as I should have been which is how I mistakenly thought I had switched the B737. I might have slant zeroed his data block by accident while issuing a frequency change to another aircraft. I clearly remembered switching the B737 and getting an acknowledgment until I listened to the tape!

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.