Date: 201606
Local time of day: 1801-2400
Location: ZLA.ARTCC, CA
Light: Daylight
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZLA
ATC / advisory: Center ZLA
Reporter organization: Government
Reporter function: Instructor; Enroute
Reporter qualification: Air Traffic Control Fully Certified
Second reporter function: Trainee; Enroute
Anomaly: ATC Issue All Types; Airspace Violation All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic
Contributing factors: Airspace Structure; Procedure
Primary problem: Procedure

Narrative: I was training a developmental. We had a radar assist with little experience. The radar controller at sector 33 has very little experience and they were training on his assist side at d-33. Sec 32's airspace starts at 34000 feet. D-33 flashes Aircraft X to us out of 150 climbing and somehow either my developmental or our d-side takes the handoff that early. After a couple minutes the radar controller at sector 33 says he would just keep Aircraft X because he was climbing so slow and we just accepted a point out climbing to 35000 feet. We never flashed Aircraft X back to sector 33. Sector 33 climbs Aircraft X to 35000 feet and after a few minutes ships him to ZLC 44 because he thought they had radar contact with him. Neither me; my trainee; nor assist controller realized we still had control of the data block. Aircraft X then starts to conflict alert flash with a LAS arrival coming from ZLC 44 at 32000 feet. Aircraft X was still climbing out of 28000 feet and the data block still reflected he was climbing to 35000 feet right into the LAS arrival. Not I; the developmental; or the assist questioned the radar controller at sector 33; because we all assumed that sector 33 was taking care of it. After Aircraft X was 4 miles into ZLC 44's airspace and still climbing out of 29000 feet; ZLC 44 called our assist and said that they were talking to Aircraft X and they stopped him below the LAS arrival. There were a lot of things that went wrong in this situation. Lack of experience has a lot to do with this. I should have realized that we still had control of the data block and had my developmental either handoff back to sector 33 or handoff to ZLC 44. I was always trained not to assume anything in this job. I assumed that sector 33 was taking care of traffic in their airspace without questioning. The auto handoff flash must not have worked to ZLC 44 or this wouldn't have happened. ZLC 44 should have called sector 33 when Aircraft X checked on their frequency or sent him back to sector 33 and none of this would have happened. There was a lack of teamwork everywhere and it all could have been avoided.


Second narrative: [Report narrative contained no additional information.]


Synopsis: ZLA controllers reported believing they had handed off an aircraft to the adjacent ARTCC; but the handoff had not been completed. The adjacent Center Controller had to restrict the aircraft's climb for opposite direction traffic.