Date: 201910
Local time of day: 1201-1800
Location: C90.TRACON, IL
Flight conditions: VMC
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ORD
ATC / advisory: TRACON C90
Second aircraft: Commercial Fixed Wing
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Workload; Confusion; Communication Breakdown
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Became Reoriented
Contributing factors: Aircraft; Company Policy; Human Factors
Primary problem: Company Policy

Narrative: Air Carrier X Flight ABCD was next to turn base behind Air Carrier Y Flight EDEC. Air Carrier X Flight ABCF was behind Air Carrier X Flight ABCD. Seconds before I could turn Air Carrier X Flight ABCD base; a pilot checked on as Air Carrier Z Flight GHCC leveling at 7;000 feet. Air Carrier Z Flight GHCC was just entering the descent area so I descended him to 5;000 feet. During the read back; the pilot stated the altitude to descend to and his call sign as Air Carrier Z Flight CEDG. Air Carrier Z Flight CEDG was the aircraft behind Air Carrier Z Flight GHCC and would have descended in to the departures had he descended to 5;000 feet. I corrected the altitude for Air Carrier Z Flight CEDG to maintain and received the correct read back. The situation I had to work through caused by Air Carrier Z Flight CEDG checking in as the aircraft in front of him caused me to be late turning base. I glanced down at my flight progress strip and read off an instruction to Air Carrier X Flight ABCF to turn right heading 020. As I was clearing Air Carrier Y Flight EDEC for the approach I noticed the wrong Air Carrier X aircraft was turning base. I issued an immediate turn to Air Carrier X Flight ABCF. He did not respond the first time; so I re-issued the immediate turn and issued traffic. Air Carrier X Flight ABCF turned to avoid and reported the aircraft on approach in sight. I could not descend the Air Carrier X aircraft or climb him due to traffic at 4;000 feet landing a parallel runway and traffic descending through 6;000 feet to the other parallel runway. I vectored Air Carrier X Flight ABCF back to the approach without further incident.What started this even was the two Air Carrier X aircraft with almost identical callsigns. If they were different I do not believe I would have turned the incorrect aircraft. Also; the Air Carrier X pilot who checked on using the callsign of the aircraft in front of him caused confusion and required immediate action by me to ensure that he would not descend into departure traffic. Ultimately; I did not take the time to ensure that I had turned the correct aircraft; especially knowing that the call signs were almost identical.




Synopsis: C90 TRACON Controller reported giving vectors to the wrong aircraft; resulting in a traffic conflict. Similar callsigns were cited as a contributing factor.