C90 TRACON controller reported giving vectors to the wrong aircraft; resulting in a traffic conflict...

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.

Original NASA ASRS Text

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

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.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1695426
Time
Date	201910
Local Time Of Day	1201-1800
Place
Locale Reference	C90.TRACON
State Reference	IL
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Approach
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 2
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Published Material / Policy

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