Date: 201508
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Light: Daylight
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Second aircraft: Regional Jet 900 (CRJ900)
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Workload; Troubleshooting; Communication Breakdown
Second reporter function: Enroute
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Detector: Automation Aircraft RA; Automation Aircraft TA; Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Contributing factors: Aircraft; Procedure; Human Factors
Primary problem: Human Factors

Narrative: Aircraft Y was handed off to me from the low sector climbing to FL230. I climbed Aircraft Y to his requested altitude of FL360. I left him on his filed route. I initiated the handoff and subsequently transferred radio communications after receipt of the handoff. I accepted the handoff on Aircraft X around the same time. Aircraft X checked in at FL370 deviating right of course. I believe I issued the weather in the vicinity of ZZZ. I noticed that the other sector ha[d] authorized Aircraft Y to deviate for ZZZ1 Airport. I did not yet apply merging target procedures as the aircraft targets did not appear to be merging even though they were deviating. As soon as I noticed Aircraft Y Leave FL360 for FL363 I issued the traffic to Aircraft X. I was informed by Aircraft X that he was already in a left turn do to an RA he had received. After the aircraft passed each other; Aircraft X returned to his normal course and continued to deviate. The pilot of Aircraft X queried me as to what had happened. I told him a CRJ900 (no numbers given) had exceeded his assigned altitude. The pilot then asked me for Aircraft Y numbers. I told him I couldn't give that over the radio. He asked for and was provided a phone number to call the facility. I don't [know] why it happened. Aircraft Y read back his altitude assignment of FL360. I was told he checked in with Sector XX climbing to FL360. Either the pilot was responding to a TCAS climb; he just made a mistake and kept climbing on his own or he took someone else's climb. The TCAS climb doesn't make sense though as there was no aircraft below him in his vicinity.


Second narrative: Aircraft X was level at FL370 and had been switched to [next] sector. Aircraft Y was climbing to assigned altitude of 360 and was cleared to deviate right of course when able ZZZ1. At XA:54 I observed Aircraft Y mode-C showing FL363 with Aircraft X at 12:30 [position] and about 5.5 miles opposite direction slightly to the right. Because he was right under a B737 (at 390) I thought it was a mode-c swap. I asked Aircraft Y to verify he was level at FL360. There was no response. The next hit showed a mode-C of FL367 and Aircraft X was at 1 o-clock and about 3 miles. I again asked Aircraft Y to verify he was level at FL360. Again there was no response. The next hit was at FL369 with Aircraft X at 3 o-clock and less than 2 miles. When Aircraft Y got back to FL365 I again called the aircraft. This time as the plane was leveling at FL360 the pilot responded that they 'were trying to avoid an RA.' When questioned the pilot said that they had gotten a descent RA at about FL357 and then got a climb RA and that was why they went above FL360.


Synopsis: With twelve o'clock traffic an A320 at FL370; a CRJ900 climbing to FL360 responded to a TCAS RA 'DESCEND' annunciation which changed to 'CLIMB' as the descent began. The A320 responded to the TCAS RA from the climbing CRJ900. The CRJ900 TCAS did not display the A320 until the RA activated.