A319
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 1.7
Time Pressure; Human-Machine Interface; Situational Awareness; Distraction; Confusion; Communication Breakdown
ATC Issue All Types; Airspace Violation All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Equipment / Tooling; Procedure; Human Factors
I was R-side sector 16. Aircraft X; had checked on just after I took the position at FL380. About 6 minutes later I gave Aircraft X 'descend and maintain 240'. As I issued the instruction I put 240T380 in the Data block and handed off to Sector 9; which was the sector below me where the aircraft would be worked until reaching Approach. The aircraft however never read back the instruction. I tried to reach the aircraft numerous; probably 5 planes on my frequency and made a call on guard to return to 135.45. Again; the aircraft never read back descent to FL240. I then saw that Sector 9 had taken the hand off and put 110T380 in the data block. At that moment I called Sector 9 and asked if they were talking to him; which they replied 'affirmative'. I then determined that either Aircraft X went to the next frequency without reading back an instruction or being told to change frequencies; or he checked on level with Sector 9 and they gave him a descent through my airspace. I then requested to go listen to the tapes. After doing so; found out that Aircraft X left my frequency and went to Approach; who then reached out to Sector 9 asking what frequency he should be on. Sector 9 gave them their frequency. Aircraft X then checked on saying 'Center; this is Aircraft X; we got lost somewhere with Center in there'. Sector 9 then gave a descent to 110 without verifying Aircraft X's altitude; thus descending them from FL380; since they never received the descent to FL240 and never read it back. It is implied from the data block that that clearance was given; but the instruction was never read back; and had never been verified by Sector 9; no control was released from me on sector 16; and no verification was done with the aircraft.
Seattle Center Controller reported an airspace violation when an aircraft left their frequency and called another sector; which then descended the aircraft without permission.