Air carrier flight crew reported miss communication referencing visual on traffic confliction resulted in failure to follow RA and NMAC situation.
Synopsis
Air carrier flight crew reported miss communication referencing visual on traffic confliction resulted in failure to follow RA and NMAC situation.
Narrative
ATL Approach had assigned us the visual to 9R from the GNDLF2 arrival and was vectoring us onto final. Approach had also been stepping us down from 8;000 to 5; 4; and then 3. The FO was PF and I was PM. It was dusk and a bit hazy and we were having difficulty picking out the airport; so we had not reported it in sight yet. We were level either at 4;000 or 3;000 when Approach told us of unidentified VFR traffic at our 11 o'clock and below us. I searched outside for the traffic and the FO pointed out the front windshield; so I assumed that he had located the traffic. I reported traffic in sight" and could see it closing in on TCAS. A few seconds later; TCAS gave us a "Maintain Altitude" RA. The FO continued on at our current altitude. Approach reported that the VFR traffic would pass behind us and gave us another turn to intercept final. I saw the traffic visually at that point. [An] aircraft slightly below us coming down our left side but turning towards us to pass immediately behind us. TCAS issued a "climb" command; but I told the FO that I had the aircraft in sight and that it would pass behind us so he could disregard the RA and maintain altitude. The RA cleared within a couple of seconds and we continued the approach to landing without further incident. The next morning I consulted the FOM for required reports and realized that I should have called Dispatch and the Maintenance Operation Manager immediately after that flight (if we consider this a near midair incident).Cause: The primary cause of the incident was the GA traffic that was operating within Class B airspace without establishing communication with ATC. However; other contributing factors were the limited visibility (dusk; haze; and the plane didn't have landing lights on); and lack of clear communication within the flight deck. It turns out that when the FO pointed while I was talking to Approach; he was indicating that he had the field in sight; not the traffic. Consequently; I reported "traffic in sight" when we did not in fact have it in sight yet. For his part; he assumed that my "traffic in sight" call indicated that I had the traffic in sight.Suggestions: Unfortunately; we cannot control what inexperienced or careless GA pilots may do. We often brief GA traffic as a threat when going into smaller airfields; but we must remain vigilant for it even in the vicinity of larger airports. The FO was right for not interrupting me verbally during a radio call; but as soon as I stopped talking; he could have specified; "field in sight." For my part; I should have verified with him that he had the traffic in sight before I reported that to Approach. Non-verbal communication can often be misinterpreted; so it should always be followed up with standard verbal clarification."
Second reporter narrative
While intercepting the Localizer for 9R; ATC advised us of traffic off of our left a few miles out. At the same time; I was looking for ATL so I could call it in sight for the visual approach. Since this was a short flight; I felt a little rushed; and was being quick with communications so as to not 'get behind the aircraft'. I pointed to the airport; without speaking; since my captain was pm and responding to the call. We had previously been scanning for the airport; and I did not have it in sight so we had not yet verified 'Field in sight' with ATC. My captain mistook this pointing gesture for me seeing the traffic; and thusly reported traffic in sight. We then got a TCAS TA for traffic off of our left; and we began looking for it. It was dusk; so it was difficult to see. Then; we got an RA to hold altitude. Right when my captain saw the traffic; we got an RA to climb. Since my captain had traffic in sight 400 feet below I made no corrections to our course or altitude; and we continued on the approach to make an uneventful landing.Cause: Poor communication and poor visibility due to dusk. Pointing my finger instead of verbally confirming airport in sight led to confusion of traffic in sight. Once that was cleared up; dusk conditions made it difficult to spot traffic.Suggestions: In the debrief; we talked about using both language and body language (pointing) to portray a better idea of what we are trying to get across. I will also wait until PM is finished talking to ATC to confirm airport in sight or traffic in sight; as opposed to multi-tasking and getting each other confused. Additionally; taking our time in communications instead of rushing when we feel task saturated.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.