Date: 201909
Local time of day: 0601-1200
Location: ZTL.ARTCC, GA
Aircraft: Citationjet (C525/C526) - CJ I / II / III / IV
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZTL
ATC / advisory: Center ZTL
Second aircraft: Citation V/Ultra/Encore (C560)
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Situational Awareness; Communication Breakdown; Confusion; Troubleshooting; Training / Qualification; Distraction
Second reporter function: Enroute
Anomaly: ATC Issue All Types; Conflict NMAC; Deviation / Discrepancy - Procedural Other / Unknown
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Air Traffic Control Separated Traffic
Contributing factors: Company Policy; ATC Equipment / Nav Facility / Buildings
Primary problem: ATC Equipment / Nav Facility / Buildings

Narrative: I was working the Radar position at a Low sector. The sector above my sector had an extremely loud test tone on [frequency] that was placed in the speaker. The sector then experienced a complete frequency failure. The area workload frequency was assigned to my sector. I quickly looked at the high sector and asked an air carrier to communicate on the high sector frequency for all aircraft to transfer to my frequency. I noticed that Aircraft X was still climbing into Aircraft Y and the two aircraft were on a collision course. I asked Aircraft Z to transmit a traffic alert on frequency for Aircraft X to turn right immediately. Aircraft X turned right and Aircraft Y climbed about a minute before collision. This near collision was caused by a catastrophic loss of communications. Communications testing was being conducted during an extremely busy period. The frequencies have been not working properly for quite some time. Test and repair frequencies during the mid-shift when the sector is not so busy.


Second narrative: I was working a D side (Radar Assist) and we were very busy. The sector was showing 25 aircraft on frequency and was red. We suddenly got a very painful sharp tone in our headsets and all of our frequencies failed simultaneously. The BUEC (Back Up Emergency Communications) had already been released to Maintenance. The standby radios failed when we tried to use them; they were un-selectable. We resorted to using guard frequency to try to climb Aircraft X above the traffic as they were merging. Another sector gave us their backup frequency as a new primary though this took a moment. We continued to use guard as the aircraft converged. Another sector contacted Aircraft Z tell all aircraft to come up on our new frequency. As this continued the sector relayed a traffic alert through an Air Carrier and turned Aircraft X via traffic alert. We continued to fight for communications with all aircraft though. This led to a NORDO military aircraft. We eventually resettled the sector. This is not the first time we have had communication failure issues in this sector. We have been reporting it the whole time I've been at this Center.


Synopsis: ZTL ARTCC Controllers reported a loss of communications on primary and backup frequencies; resulting in an NMAC.