Date: 201905
Local time of day: 1801-2400
Location: DFW.Tower, TX
Flight conditions: VMC
Light: Dusk
Aircraft: A321
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B DFW
ATC / advisory: Tower DFW
Aircraft component: Autothrottle/Speed Control
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Communication Breakdown; Situational Awareness
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Overcame Equipment Problem; Flight Crew Regained Aircraft Control
Contributing factors: Human Factors; Aircraft
Primary problem: Aircraft

Narrative: I was hand flying an A321. The auto pilot and auto thrust were turned off on base- visual approach to DFW 18R; good weather light winds.Completely configured; about 1500 ft agl; DFW tower called out traffic less than two miles; a helicopter has you in sight will be crossing left to right below you. We looked but did not see the traffic initially.At about 1000 ft the TCAS said; 'Monitor vertical speed.' At that time I saw the helicopter below us and slightly to my left as it crossed our final. (It would later cross directly underneath us). We turned off the flight directors as this is the first step in reacting to an RA; but there were no further warnings or alerts from the TCAS. On the airbus; TCAS alerts are inhibited below 900 ft.With no RA to follow and having seen the helicopter emerge soon our right side I elected to continue the visual approach. We then received a master caution (approx 500 ft) for something about auto thrust. For the remainder of the approach and landing we kept receiving master caution lights about the thrust system. As I was hand flying with auto thrust off; to me it seemed like some kind of a nuisance caution light. But then I realized the thrust levers were not behaving normally; they were not controlling the engines as expected. I would move the levers all the way up to the climb detent and the thrust would remain low. Just before landing (this entire episode didn't take very long) my very sharp FO (First Officer) said 'The auto thrust is back on; it's controlling the thrust; that's why we keep getting the caution lights.'The landing was uneventful. We were aware the aircraft had the AP/FD TCAS modification. Part of this modification is that during an alert; the auto thrust becomes armed or active; depending on the thrust levers position. This; coupled with the TCAS RA being inhibited immediately after alerting us created an unusual situation for the final 900 ft of our approach. Current procedure is to fly TCAS events on aircraft with this [modification] the same as aircraft without. Shut off the AP and flight directors and fly the aircraft out of the situation. I had never considered this particular situation before and I believe my fellow pilots could learn from it.Also; I don't know what was so important about the helicopter's flight (perhaps it was transporting someone to the hospital) that required it to fly so close to us on short final while we had almost 200 souls on board; but I believe the tower could have found a safer course of action here. Some acts cause unintended consequences. I'm glad this one ended safely.


Second narrative: [Report narrative contained no additional information.]


Synopsis: A321 flight crew reported an auto thrust issue following a traffic conflict on final approach.