Date: 201902
Local time of day: 1201-1800
Location: ZAU.ARTCC, IL
Flight conditions: Mixed
Light: Daylight
Aircraft: Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B ZZZ
ATC / advisory: Center ZZZ
Second aircraft: Large Transport
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Flight Engineer; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Situational Awareness; Fatigue; Confusion; Communication Breakdown
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft RA; Automation Aircraft TA; Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Human Factors; Procedure; Airspace Structure
Primary problem: Procedure

Narrative: On the RKCTY 1 RNAV arrival; we had leveled FL310 at HOOTA. Chicago Center gave us clearance to descend to FL200. Clearance was very clear and read back from First Officer was also very clear. I started a managed descent to FL200. I saw an aircraft on TCAS opposite direction some distance out slightly diverging track. I judged that a better rate of descent was required; so went to open descent and increased speed from 310 to 320 knots. I commented that ATC was cutting our separation pretty close (3 1/2 miles diverging) and was about to ask First Officer to query Chicago [Center] when he issued us a turn 20 degrees left. I was already in the process of reaching to do that. ATC said we were cleared to FL270. We stated we were cleared to FL200 and were very clear in our read back. Nothing further was said.We did receive a TCAS TA and complied with all procedures. We were aware of aircraft at all times. We did not receive a TCAS RA.There was a [Company aircraft] on arrival somewhere ahead of us; and in hindsight; it is possible that Chicago [Center] had intended the descent clearance for that flight but used our number. We were all very clear about the clearance in our cockpit; including the augment crew who were contributing throughout the flight as required.We had no uncertainty about the clearance in our cockpit so nothing could have been done to change that.Our read back was very clear so ATC hearing that would have trapped the error. In addition; once I realized that the crossing altitudes and diverging tracks appeared outside the norm and near the edge of the separation envelope; I should have been more aggressive in asking ATC what their plan was. Was fatigue a contributor - maybe. We had only been back on duty about 20 minutes after our break and sleep inertia always dulls the edges of our senses somewhat; though both of us felt well rested.Another contributor is the fact that these RNAV arrivals were designed to be flown; as is; in managed NAV. That seldom happens. We are always being requested to change speeds; change altitudes from published; or being vectored off/on course. Therefore; receiving a descent clearance that doesn't quite match up with the arrival is not at all unusual.




Synopsis: Air carrier Captain reported receiving an RA after ATC confused similar sounding call signs.