Date: 201902
Local time of day: 1801-2400
Location: DFW.Airport, TX
Flight conditions: VMC
Light: Night
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Climb
Airspace: Class B DFW
ATC / advisory: TRACON D10
Aircraft component: Traffic Collision Avoidance System (TCAS)
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: On climbout from ZZZ passing thru approximately 6;000 feet; ATC called out traffic at our 1:00 above us and descending. I thought I had the traffic visually; but wasn't sure; so I responded 'searching.' I looked at the TCAS (Traffic Collision Avoidance System) display; but there wasn't a target where I thought the traffic should be. At approximately 7;000 feet; we got a Resolution Advisory telling us to descend; followed by another telling us to increase descent rate. The FO (First Officer) complied with the RA (Resolution Advisory) and performed the descending maneuver. The TCAS display showed an aircraft right on our nose within 100 feet vertically. I called ATC and informed them we were descending in response to an RA. We descended approximately 1;000 feet during which time the TCAS continued to command a descent. After that 1;000 feet; the TCAS commanded Climb/Climb Now. The FO complied with the climb RA command. The target on the display continued to show an aircraft on our nose within 100 feet; and we began to realize that our TCAS system was more than likely malfunctioning. I switched the transponder XPNDR and ALT SOURCE both to '1' (they had been both in '2') and the displays returned to normal. I informed ATC that it was likely an aircraft malfunction we were responding to; and he confirmed that he did not observe any traffic in our immediate vicinity and altitude. We continued the flight in system 1 with no other issues.


Second narrative: Climbing via the AKUNA7 departure; ATC called out arrival traffic to us; and those aircraft were visible on the ND (Navigation Display). Several seconds later; a new target appeared; followed by a 'traffic; traffic' TA (Traffic Advisory) and then a descend RA (Resolution Advisory) immediately afterward. Captain advised ATC we were responding to RA. I descended the aircraft according to PFD (Primary Flight Display) indications; and continued to receive guidance to increase rate of descent. Thrust was at idle with speed brakes deployed; aircraft exceeded 250 kias below 10;000. After several seconds; TCAS commanded a 'climb; climb now' reversal; which I complied with. After several more seconds; the captain and I realized the target on the ND was stationary on our nose and continually indicating our altitude. ATC advised no targets in our vicinity. Captain and I discussed that we may have a TCAS malfunction; and he switched transponder to Number 1. All TA/RA indications disappeared. Switching back to Number 2 caused an immediate false RA. Advised ATC of equipment malfunction and returned to clearance in coordination with ATC. Discrepancy written up in aircraft logbook.Faulty TCAS indication when Number 2 transponder selected.


Synopsis: B737-800 flight crew experienced erroneous TCAS alerts during climbout due to apparent equipment malfunction.