Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (mon) 8
Confusion; Communication Breakdown
ATC Issue All Types; Airspace Violation All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance
Procedure; Company Policy
I was working the R-side on Sector XX. I had an Air Carrier X and Air Carrier Y both on frequency at the same time; both landing at LAS. I was not aware of the similar sounding call signs. I gave Air Carrier X a decent clearance to cross an intersection at FL160 250 KTS. Air Carrier Y took the clearance and began descending from FL310. I did not catch this until I saw Air Carrier Y about a mile inside my airspace descending out of FL298. I instructed Air Carrier Y to maintain FL290 and reissued the descent clearance to Air Carrier X. I believe Air Carrier Y began its descent while he was still in another centers airspace.I recommend that the airlines adjust their call signs so they are not so similar or space out these flights numbers so that they are not in the same area at the same time.
Similar sounding call signs caused the wrong aircraft to begin a descent in another Centers airspace.