Narrative:

[There were] several crossing/conflicting traffic situations. Aircraft Y was handed off via automation to and communications transferred to sunol sector. I had taken radar contact via automation on aircraft X inbound to mhr from sunol. Aircraft X had not checked in on my frequency. I last noticed aircraft X descending through 16000 ft. Standard operating procedure is 'descending to 14000 or lower filed altitude'. I was resolving other conflicts when the collision avoidance (ca) alarm sounded. Aircraft X was descending through 11800 and was within 5 miles of aircraft Y on a converging course. I broadcasted to aircraft X to stop descent and climb immediately to 12000 ft and issued the traffic (aircraft Y). Aircraft X was on frequency; responded and complied. Recommendation; comply with the SOP and 7110.65. Transfer communication prior to entering the receiving controller's airspace.

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Original NASA ASRS Text

Title: NCT Controllers described a loss of separation event when late night airspace configurations were not clearly understood leading to confused coordination and the error.

Narrative: [There were] several crossing/conflicting traffic situations. Aircraft Y was handed off via automation to and communications transferred to Sunol Sector. I had taken RADAR contact via automation on Aircraft X inbound to MHR from Sunol. Aircraft X had not checked in on my frequency. I last noticed Aircraft X descending through 16000 FT. Standard Operating Procedure is 'Descending to 14000 or lower filed altitude'. I was resolving other conflicts when the Collision Avoidance (CA) alarm sounded. Aircraft X was descending through 11800 and was within 5 miles of Aircraft Y on a converging course. I broadcasted to Aircraft X to stop descent and climb immediately to 12000 FT and issued the traffic (Aircraft Y). Aircraft X was on frequency; responded and complied. Recommendation; comply with the SOP and 7110.65. Transfer communication prior to entering the receiving Controller's airspace.

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.