Date: 201901
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
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: A320
Aircraft component: Traffic Collision Avoidance System (TCAS)
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude
Detector: Automation Aircraft TA; Automation Aircraft RA; Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: The aircraft was in cruise at FL360 in clear conditions. I noticed a message on the ND (Navigation Display) that said 'decrease range TCAS.' When I decreased the range on the ND the TCAS showed a TA in yellow. The aircraft was at our altitude climbing very slowly. The target changed to a descend RA. The FO (First Officer) and I followed SOP and complied with the RA. I notified Center that we were deviating from our clearance due to an RA. We descended about 200 feet when I visually acquired the aircraft flying over us. At this point the target was 1000 feet above us according to the TCAS display. When we were clear of conflict; we climbed back to our previously assigned clearance and notified ATC. There were no aural warnings at all from the TCAS system. When we arrived [at our destination]; we wrote up the TCAS. Maintenance repaired the system and it tested good with the 'TCAS system test OK' aural message.


Second narrative: We were level at FL360; approximately 30-40nm SE of ZZZ VOR; on a direct course [along our route]. Aircraft Y received a clearance to climb to FL370. I am unsure of their starting altitude. The CA (Captain) first saw the TCAS icon indicating a RA (red square) on the ND (Navigation Display) and brought it to my attention. It showed Aircraft Y level at FL360; head on with our track at our altitude. Unbeknownst to us; a TCAS circuit breaker had tripped prior to this event; causing it to not generate any aural warnings for traffic. It took both of us a moment or two to process what was happening due to no aural alerts. I immediately executed the TCAS RA escape maneuver and initiated a shallow descent per the green VSI indications. We descended approximately 200 feet and Aircraft Y executed a rapid climb. We cleared each other by 1100 feet as we crossed each other. The controller implied that Aircraft Y had overly delayed their climb to FL370. I queried ATC about the clearance Aircraft Y had and received no response; as if the incident never happened. Once at the gate; we called MX (maintenance) and they noticed the circuit breaker that tripped after we left [our departure airport].


Synopsis: A320 flight crew reported a TCAS malfunction during an airborne conflict situation.