Airbus Industrie Undifferentiated or Other Model
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 4
Workload; Communication Breakdown; Training / Qualification
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Equipment / Tooling; Human Factors; Procedure
I was working R27 and R36 combined; just went through a pretty busy push with D-side training going on. I had several aircraft deviating for weather and turbulence. I had to repeat myself to at least 6 or 7 different aircraft during this session; at the time I wasn't aware that other controllers were having issues with the frequency's for both sectors. I had Aircraft X depart out of CLT [bound for Europe]; I climbed the aircraft to FL270 on initial contact; [and] then I climbed Aircraft X to FL300 to step him up reference traffic! Once the aircraft was clear I then climbed him to FL350 the requested alt; Sector 16 had traffic on J14 going to ZZZ at FL350; Sector 16 coordinated with the D-side trainee to stop Aircraft Z at FL340; the d-side then told me.  Once I was told I transmitted to Aircraft X to amend the altitude to FL340 for traffic. I was sure that the aircraft got the altitude change and he read it back; a couple other clearances went out and the soup wanted Sector 27 to get split out. I assumed everything was fine because the d-side; the trainer and myself all thought Aircraft X took the amended clearance; no one told me any different so; right before I started my relief briefing I switched the Aircraft X which I found out later the aircraft did not get the frequency change. Then I gave my relief briefing and they split out Sector 27; after I got up the trainer told me that Aircraft X got with Aircraft Y going to ZZZ on J14 around the CREWE intersection. I was not aware that Sector 16 did not have the aircraft; Aircraft X ended up still being on Sector 27's frequency after the sectors were split. Aircraft X climbed to FL350 which is the altitude the Aircraft Y was at; both aircraft got a RA or TCAS event!I missed that Aircraft X did not get the altitude change so that is my fault; but I definitely think the frequency issues at both Sectors 27 and 36 were a contributing factor in this issue.
I was on position for 5 to 10 minutes and settling in to the session. Aircraft X was a hand off to me climbing to FL350. Aircraft Y was already level entering from another sector. I requested Aircraft X to be amended to FL340 and updated accordingly while accepting radar. My flight strips were current as to which aircraft was on frequency. Aircraft X was not; but I knew this. The previous sector was opening up the low side and changing controllers. I chose to wait until they had time; trying not to distract; them to request communication. It was when Aircraft X was about two minutes into the sector I made this request. They responded they did not have the aircraft on frequency. During this same time I called the Airbus traffic to Aircraft Y at 2 o'clock and 2 miles climbing to FL340. Aircraft Y responded traffic in sight. Knowing that the sector was recently split; I called the low sector to find Aircraft X. Seconds later Aircraft Y asked if it was stopping the climb and Aircraft Y responded to a TCAS RA with a climb to FL355. I observed Aircraft X climbing to FL343. Aircraft Y then asked for a climb since Aircraft X was still not on frequency to resolve the situation. I issued the requested altitude and notified the supervisor of the TCAS event. Aircraft X checked then checked on frequency level at FL340. I feel we need to focus more on splitting out sectors and ensuring aircraft are on appropriate frequencies. It is frustrating that the traffic was not overlooked and this could have been resolved if the clearance was received. I am still new to the facility; but have been certified long enough to start developing opinions. Several times I have taken control of two sectors only to be immediately asked to split one off. This should have been done while the previous controller had the picture. I am not sure the in the order things happened in this event; but that aircraft was not on the frequency giving the clearance.
Reporters' state loss of separation between two aircraft due to main aircraft not acknowledging altitude change. Frequency problems and weather may be attributable factors.