Narrative:

End of shift; supervisor was combining sectors into the midnight configuration. I had just assumed the adjacent super high sector. I was now working sectors 38 and 39. These sectors have a base altitude of FL330. After a while the supervisor came around and told me; 'you have it all.' I took that to mean I was also assuming the intermediate highs ( fl 240-FL320). I looked down to the controller who was at that sector and saw that he/she was turned away from the scope and talking to a trainee. I believed I then indeed had that airspace. A minute later I descended air carrier X from my base to fl 290 to meet the LOA for boston center. Immediately upon descent the conflict alert went off with an aircraft at FL320. I then saw the controller react and then realized he/she was indeed still open. I heard him/her turn her aircraft left. I turned my aircraft 60 degrees north. Loss of separation occurred with 3 miles and 300 feet. Recommendation; its hard to say since the error occurred due to my perceived 'sectorization.' this is a routine that is followed every night and a lack of specific awareness as to who was still open led to my error. From the supervisor's standpoint; to announce from behind me that I 'had it all' was vague and led me to assume that which was not true. However; that does not release me from the fact I still had clues that the sector was open below me; i.e. I had not assumed the frequencies. This is simply an awareness issue that demonstrates complacency and attention to detail can lead to this type of error.

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Original NASA ASRS Text

Title: ZOB Controller experienced loss of separation event when he/she assumed adjacent airspace was combined and descended traffic; resulting in a confliction. Corrective action was too late.

Narrative: End of shift; Supervisor was combining sectors into the midnight configuration. I had just assumed the adjacent super high sector. I was now working sectors 38 and 39. These sectors have a base altitude of FL330. After a while the Supervisor came around and told me; 'you have it all.' I took that to mean I was also assuming the intermediate highs ( FL 240-FL320). I looked down to the Controller who was at that sector and saw that he/she was turned away from the scope and talking to a trainee. I believed I then indeed had that airspace. A minute later I descended Air Carrier X from my base to FL 290 to meet the LOA for Boston Center. Immediately upon descent the conflict alert went off with an aircraft at FL320. I then saw the Controller react and then realized he/she was indeed still open. I heard him/her turn her aircraft left. I turned my aircraft 60 degrees north. Loss of separation occurred with 3 miles and 300 feet. Recommendation; its hard to say since the error occurred due to my perceived 'sectorization.' This is a routine that is followed every night and a lack of specific awareness as to who was still open led to my error. From the Supervisor's standpoint; to announce from behind me that I 'had it all' was vague and led me to assume that which was not true. However; that does not release me from the fact I still had clues that the sector was open below me; i.e. I had not assumed the frequencies. This is simply an awareness issue that demonstrates complacency and attention to detail can lead to this type of error.

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.