Commercial Fixed Wing
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 26
Communication Breakdown; Situational Awareness; Confusion
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Requested ATC Assistance / Clarification
Airspace Structure; Human Factors
I was working a radar sector and a D Side (Radar Assist) had just sat down next to me to help. Aircraft X checked on level at 37;000 feet. I scanned my scope and didn't see a data block with that aircraft. I displayed a route using the call sign and noticed it was coming from west of my airspace; but it was off my screen. I told Aircraft X to go back to his previous frequency. Because he sounded a little confused I expanded my radar screen and saw his data block approximately 50 miles west of the Center boundary. His data block showed FL370 descending to FL350; but he checked on level at 37;000 feet. I immediately told him to stay on the frequency. His data block started to flash with Aircraft Y also level 37;000 feet. My D Side began to call the adjacent sector to advise them we were going to descend Aircraft X to 35;000 feet. I was able to descend Aircraft X to keep separation. Remember Aircraft X was transferred to my frequency without a handoff.
ZMP Center Controller reported that the adjacent Center ZDV transferred an aircraft to their frequency without a proper handoff; resulting in an airborne conflict.