Medium Large Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Workload
Aircraft Equipment Problem Less Severe; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Executed Go Around / Missed Approach; Flight Crew Took Evasive Action
Aircraft; Human Factors
We had 3 runway changes as we were getting closer to BOS. FO was flying. I told the FO at all 3 times that he would continue flying the plane (since the first change we were descending via the arrival and I wanted him to pay attention to the VNAV and all speed restrictions). As we passed PROVI; we were given a left turn. The controller gave us a runway change to 4R from 22L. I again told the FO; I would do the all the FMS changes and would brief the ILS. When we switched to the final controller; he gave us 4L visual approach. I again did the FMS changes. The FO told me that he had never done the visual approach to 4L. I explained to him that there was an FMS RNAV but we did not have that approach on the EFB; however; we could use it as a backup to the visual approach. I also told him [not] to worry that I would walk him through it.During all these changes; we were told to look for traffic to follow. I was dividing my attention between being heads down reprogramming the FMS and looking outside at night for traffic to follow (which was the plane that would be parallel to us on a visual to RWY 4R). ATC told us to slow to 190 knots and a descent to 4;000 feet. Once we had the traffic in-sight; the controller gave us the visual approach; a turn towards the airport; told us to maintain 170 knots to 5 mile final; cross the 10 DME at or above 3;000 feet; and to contact tower at 128.8. I was trying to make all the appropriate FMS changes for intercept the course; keep the airplane on 4R in-sight; make all the configuration changes that the FO was calling for (gear; flaps; speed and altitude on the guidance panel and to draw a 10 mile ring on the moving map to identify the 10 DME/3000 feet restriction).The frequency was extremely busy since we had been with BOS Center since they were giving everyone basically S-turns because of the runway changes and with approach as they were getting saturated funneling everyone with the runway changes. As we were on the final phase of intercepting the 10 mile ring; the final controller told us that he needed us going directly to the runway. I told him that we were and that we were turning through a heading of 070 already. As we started the final descent; I told the FO to disconnect the autopilot and to hand flying it and to use the VNAV glide path as reference and that I would give him a 3 degree descent angle to cross-reference his descent.When the autopilot disconnected; we received a very loud 'autopilot' continuous disconnect aural warning. As I have been a CA/FO on this model of aircraft for many years; I knew that the continuous aural warning is related to the trim system when the autopilot is flying. We both again pressed our respective autopilot discount buttons to try to silence the warning; but it did not stop. At the same time; we received a TCAS RA with the traffic off to our right. I believe the TCAS detected that we were both descending; with a closure rate but it cannot distinguished that we were on a very closed parallel approach. I told the FO 'My aircraft' and simply called for a go around. I manually overrode the autopilot. I called for flaps 2 and gear up as I initiated a climb. The tower noticed that we were going around and called us. I simply clicked the mike and said; 'standby'. I prioritized flying with newer FO; letting catch up with what was going on as we still trying to speak to each other on a busy frequency; with a continuous loud aural warning and reconfiguring the aircraft. A few seconds later; the tower told us to turn to the left; that if able to maintain 3;000 feet and to let him know if we needed any assistance. We complied with his instructions and told him that we had an autopilot issue and we needed to run a checklist.I called for the FO to run the QRH procedure for the autopilot aural warning. The FO successfully ran the QRH and the aural message stopped. I transfer control of the aircraft back to the FO and we were vectored back around for a normal landing. I should have turned down the visual approach for a number of reasons. A very late third change of runway; flying with not a very experienced FO; at night; how close we were to the airport and the complexity of reprogramming the FMS and doing a so-close parallel approach. I have done this approach a number of times in the daytime; but cannot recall the last time I had to do it at night. ATC was trying to keep us parallel to the traffic as we both descended. I think the TCAS sense the closure rate and that was the reason for the RA.
Air carrier Captain reported he received a TCAS RA while on a night visual parallel approach to Runway 4L at BOS; performed a go-around; and eventually was vectored around for a normal landing.