Air Traffic Control Fully Certified
Communication Breakdown
ATC Issue All Types; Airspace Violation All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance
Human Factors; Procedure
[We had] Air Carrier XXXX en route to Wyoming; and Air Carrier XYXX en route to Colorado both on frequency at the same time. Air Carrier XYXX handed off to Sector 1 for descent clearance to FL340 as per the FOP for aircraft landing Colorado. Air Carrier XYXX given the frequency change to Sector 1; Air Carrier XXXX answered the frequency change instead and the read back was missed. Air Carrier XXXX checked in at Sector 1 at FL380 and the Sector 1 Controller acknowledged Air Carrier XXXX and issued a descent clearance to FL340. Air Carrier XXXX inquired about rides at FL340; the Controller at Sector 1 then called Air Carrier XXXX; Air Carrier XYXX and issued a frequency change to Sector 3 and told the pilot to inquire about rides there. Air Carrier XXXX accepted the descent clearance and frequency change where it was noticed that the incorrect aircraft was descending to FL340 and violating the airspace of Sector 4. Appropriate action was taken to correct the descent and Air Carrier XXXX was climbed back up to FL380 and Air Carrier XYXX was descended to FL340 and shipped to the appropriate frequency. Have this Air Carrier change similar sounding call signs if they anticipate the aircraft being in the same sector at the same time.
[Narrative #2 had no additional information.]
Enroute Controller described an unauthorized descend and airspace incursion when a same company aircraft with a similar sounding flight number initiated a descent issued to another company aircraft.