Date: 201901
Local time of day: 1801-2400
Location: ZOB.ARTCC, OH
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Cruise
Airspace: Class A ZOB
ATC / advisory: Center ZOB
Second aircraft: Regional Jet 200 ER/LR (CRJ200)
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Communication Breakdown
Second reporter function: Enroute
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Provided Assistance
Contributing factors: ATC Equipment / Nav Facility / Buildings
Primary problem: ATC Equipment / Nav Facility / Buildings

Narrative: I was working a combined sector at HUD/DET. I had reports from ZAU that aircraft couldn't hear me/I couldn't hear them; so I was moving from Mains to Standby then finally to BUEC [Back Up Emergency Communications] in attempt to be able to communicate better with the aircraft. We cannot cross-couple at this sector because the western frequency is not usable on the far east side; and we don't like to use 135.72 as an alternate in case we don't switch them early enough and thus lose the aircraft.Additionally; rides had begun to deteriorate and I needed to get all aircraft at FL280 or below (I own from FL240-FL330) or up above FL340. There was a lot of changing altitudes occurring at this time. The sector beneath me (WINDSOR/DRESDEN) was helping me out by climbing aircraft from below and missing my traffic while I attempted to resolve the frequencies after I had reported issues to my supervisor.I switched an aircraft - Aircraft Y - to the next sector (RAV) right on the boundary after a call for them to accept the handoff. There was interference on the frequency during the response; but upon reviewing the tapes apparently Aircraft X took the switch for Aircraft Y. I did not hear it; and had not made the aircraft aware of similar sounding call signs ahead of time. The next sector must have missed the incorrect call sign. They descended Aircraft Y (who was not on their frequency yet; though we didn't know it) from FL260 to FL240. The sector below me had climbed Aircraft Z to FL250 beneath Aircraft X with my approval. We saw FL257 in the datablock. I immediately told Aircraft X to maintain FL260 for traffic with no response. I called again. I attempted to reach Aircraft X several times on frequency with no response.In the meantime; the sector below me stopped the climb of Aircraft Z and turned him 30 degrees left with my approval. I called a safety alert to Aircraft X and told him to turn left and climb if he could hear me. Aircraft Z responded to a TCAS RA.The controller at the sector below me and I were operating under the assumption that Aircraft X was experiencing an emergency and expedited the descent of another aircraft that might have been a problem in the future.I received a call after the traffic was no longer a factor from the sector that had Aircraft X on their frequency to tell me that he'd taken the switch for Aircraft Y. Until that point; I had no idea that there'd been a readback error.Better working frequencies; better communication with foreign aircraft and an attempt by airlines to not have such similar sounding call signs on such similar routes at such similar times. (This is a frequent problem for us with GGN) It would have also helped if either I or the controller at the RAV sector had heard the mistaken call sign of Aircraft X instead of Aircraft Y.


Second narrative: I was the radar position at the low sectors of Windsor and Dresden at ZOB. I worked a departure out of Detroit; Aircraft Z. The controller at the high sector where Aircraft Z was climbing into was having frequency issues along with congestion due to poor rides; so I decided to keep Aircraft Z on my frequency to assist the other controller. Aircraft Z was climbing to maintain FL250; because traffic Aircraft X was level at FL260. I then viewed Aircraft X depart FL260 to descend; in conflict with Aircraft Z at FL250. I issued a descent clearance to FL240 and a turn of 30 degrees right to Aircraft Z to ensure the aircraft would not merge; while not knowing what Aircraft X was descending to; as Aircraft Z was just passing FL240; I thought it best to send the aircraft back down to ensure I kept Aircraft Z below the randomly descending Aircraft X. After control instructions were given; Aircraft Z informed me he got an RA. After I ensured the aircraft was finished with his RA; I gave him follow up control instructions. It turns out Aircraft X had company Aircraft Y on frequency with the high sector. Aircraft X took Aircraft Y frequency switch and descent clearance on the next frequency; leading to the loss of separation and the RA.I think it would benefit the NAS greatly if we did something about our frequencies. We have been having trouble with the same frequencies for years now; along with proof in writing of when there are issues with them. Also; companies should not have aircraft with such similar sounding call signs depart the same airport; with the same route of flight; within minutes of each other. This creates entirely too much confusion for not only the pilots; but the controllers as well. We both have a lot going on in and out of the cockpit and I think a lot of these errors would be drastically reduced if call signs were not so similar in such a fashion.


Synopsis: Cleveland Center controllers reported radio problems along with similar sounding call signs led to and unsafe situation.