ZID ARTCC controller reported the wrong aircraft acknowledged for a new altitude assignment and the ...

Attributes
ACN	1703425
Time
Date	201911
Local Time Of Day	1201-1800
Place
Locale Reference	ZID.ARTCC
State Reference	IN
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 14.0
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

Narrative:

I climbed air carrier X flight abbb to 36;000 feet. I believe air carrier X flight aabb took the clearance and I did not realize it. I also believe that they both took the clearance but I'm not sure. Moments later I switched flight aabb frequency via cpdlc. While flight abbb was climbing into my sector I noticed that flight aabb started descending. I was not talking to flight aabb. I verbally coordinated with the sector which is located next to me that I'm stopping flight abbb at 35;000 feet and turning south and then I issued the instruction to the pilot. Then the sector I gave flight aabb to called and said that flight aabb was returning to 38;000 feet. When traffic was no longer a factor I climbed flight abbb to 36;000 feet and turned them on course. I never realized how close the call signs were until it was too late. Be more aware of similar call signs.

Original NASA ASRS Text

Title: ZID ARTCC Controller reported the wrong aircraft acknowledged for a new altitude assignment and the Controller did not detect it due to similar sounding call signs.

Narrative: I climbed Air Carrier X Flight ABBB to 36;000 feet. I believe Air Carrier X Flight AABB took the clearance and I did not realize it. I also believe that they both took the clearance but I'm not sure. Moments later I switched Flight AABB frequency via CPDLC. While Flight ABBB was climbing into my sector I noticed that Flight AABB started descending. I was not talking to Flight AABB. I verbally coordinated with the sector which is located next to me that I'm stopping Flight ABBB at 35;000 feet and turning south and then I issued the instruction to the pilot. Then the sector I gave Flight AABB to called and said that Flight AABB was returning to 38;000 feet. When traffic was no longer a factor I climbed Flight ABBB to 36;000 feet and turned them on course. I never realized how close the call signs were until it was too late. Be more aware of similar call signs.

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.

ZID ARTCC controller reported the wrong aircraft acknowledged for a new altitude assignment and the controller did not detect it due to similar sounding call signs.