Date: 201606
Local time of day: 1201-1800
Location: ZDV.ARTCC, CO
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 ZDV
ATC / advisory: Center ZDV
Second aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Distraction; Situational Awareness; Communication Breakdown
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Automation Aircraft RA; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew FLC complied w / Automation / Advisory
Contributing factors: Environment - Non Weather Related; Human Factors
Primary problem: Environment - Non Weather Related

Narrative: It was near the end of my shift; I was being told by the Controller In Charge (CIC) that the sector would be going red for about 20 minutes and was being asked if I wanted to keep a D-side (Assist Controller) or split out the upper portion of my airspace. About the same time; Aircraft X was checking on climbing out of Denver. I issued Aircraft X a clearance to 37000 feet after doing a quick scan. I then responded to the CIC that I would rather just keep a D-side. My D-side then brought my attention to the fact that Aircraft X was in conflict with Aircraft Y level at 34000 feet but had several minutes to fix the conflict.I issued an amended clearance to Aircraft X to maintain 33000 feet. About the same time I was being asked if I wanted a break. I told the CIC that I would rather stay on position until I was no longer needed in the area. Several more people were coming in and there was a lot of distractions with my D-side being relieved and also general discussion in the area about the new break board and how to work it. Aircraft X was observed climbing through his assigned altitude and creating a CA with Aircraft Y. I issued a 20 degree left turn to Aircraft X; told him to maintain 33000 feet and issued a traffic call. Aircraft X read back the clearance but reported they were at 34000 feet and would descend back down to 33000 feet. I then told Aircraft Y to turn 20 degrees left. About 5 seconds later; Aircraft X reported they were responding to an RA and they were in a climb. I asked Aircraft X to report when they were done with the RA. Aircraft X reported level at FL350 right at 5 miles from Aircraft Y and I then issued both aircraft clearances back on route.I believe that I was being asked to make several decisions at once while also trying to work traffic and with the line change with a new crew coming in; there were too many distractions that caused me to miss a readback from Aircraft X.




Synopsis: ZDV Controller missed an incorrect altitude readback from an aircraft due to distractions in the work area. The aircraft climbed into a conflict with opposite direction traffic.