Narrative:

I was the captain; pilot flying; and with the exception of a couple of small weather deviations around a line of thunderstorms; the flight was progressing smoothly. At least; until about half way across the country. On my audio panel; I had the cabin inter-phone volume up; and overheard the flight attendants discussing a medical issue with a passenger who was laying on the back galley floor due to low blood pressure and feeling faint. When the number 1 (flight attendant) called me; she said that they had made an announcement for a doctor on board; and there was one who was attending to the woman; and also it appeared that she would be 'okay'.I requested that they make a call to the physician on call (poc) using their wi-fi phone; and gave them the desk number. At that point; I also decided to contact dispatch and get them in the loop. We discussed using ZZZ if a medical diversion was required. Dispatch said the flight attendants were talking to the poc and agreed on our diversion choices if needed. First officer and I called up the weather; ATIS (ZZZ); reviewed the jeppesen; and calculated our landing distances. ZZZ would be right on the line. It was very fortuitous that we did all this pre-planning; because about 20 minutes later we had to put that plan into action.all of a sudden; there was a muffled bang sound; followed by a loud whirling continuous noise like an electric motor that was failing. At the same time; there was also a small vibration that reminded me of a radar antenna motor going bad; so I immediately switched the unit off. That wasn't the problem. Next; our number 1 flight attendant called and said she heard a large bang by the one right (1R) door. After she hung up; first officer and I both thought we had a possible aircraft structural problem that may cause a rapid decompression; and we asked for a lower altitude of 14;000 feet. At this point; we knew we probably weren't going to destination.now the noise was accompanied by an acrid electrical smell. I said let's get on oxygen and get into the smoke and fumes checklist. I handed the aircraft over to the first officer and said tell them we want to divert to ZZZ. The number 1 called to say she smelled smoke; however when I tried to communicate with her through the oxygen mask microphone; she could not understand what I was saying. There was a loud feedback squeal in the speaker when I transmitted; and further complicating the situation; she could not understand what was being said from the poor quality of the oxygen mask microphone. After several attempts with the speaker causing a large feedback squeal; I took the mask off long enough to tell her to prepare for a landing and do a '30 second review;' I also made a quick announcement to the passengers to return to their seats; and I turned the seatbelt sign back on. It was at this time I noticed that the smoke abated but the loud humming noise continued. With the smoke subsiding; I discontinued the smoke/fumes checklist after the first couple of steps. In hindsight; I should have continued beyond step 2 in the checklist; but the lack of communication distraction took me out of it until it was no longer needed.we removed our oxygen masks; briefed the approach; ran the emergency landing checklist; and discussed the situation and our threats to the remainder of the flight. With the situation a little better at hand; I 'all called' the flight attendants and gave them a proper briefing; and said we were expecting a normal landing and taxi to the gate. I made a better; more detailed public address to the passengers and explained that I requested EMS to be on hand so expect to see some 'flashing lights!' we agreed that we would shoot the ZZZ ILS and leave it on the autopilot; in case the smoke started back up again. Fortunately; it did not and we successfully shot the approach; and I disconnected the autopilot at 500 feet and got probably the smoothest landing.once at taxi speed I made a 'remain seated 3x public address' and we continued to [the] gate; and deplaned using the jetway uneventfully. Shortly after shut down while debriefing maintenance; the motor whirring noise got louder and the acrid electronics odor returned. Next; we got an ECAM 'avionics smoke' message. I followed the QRH 'immediate action' checklist and shortly thereafter; the noise stopped; but only after the 'av/vent extract fan'; circuit breaker (AC 4) popped. That concluded the evening's excitement!one final thought; first officer related an oxygen mask communications procedure from a previous airline; where they would put their headsets over the oxygen mask and turn the speakers off; hence no feedback problems! I use a molded ear-piece and believe that would also work. The current procedure with the microphone/speaker feedback is unsafe and completely unacceptable!

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Original NASA ASRS Text

Title: A321 Captain reported diverting due to in-flight smoke and fumes from an apparent electrical problem followed by difficulties communicating through the oxygen masks.

Narrative: I was the Captain; Pilot Flying; and with the exception of a couple of small weather deviations around a line of thunderstorms; the flight was progressing smoothly. At least; until about half way across the country. On my audio panel; I had the cabin inter-phone volume up; and overheard the Flight Attendants discussing a medical issue with a passenger who was laying on the back galley floor due to low blood pressure and feeling faint. When the number 1 (Flight Attendant) called me; she said that they had made an announcement for a doctor on board; and there was one who was attending to the woman; and also it appeared that she would be 'okay'.I requested that they make a call to the Physician on Call (POC) using their Wi-Fi phone; and gave them the desk number. At that point; I also decided to contact dispatch and get them in the loop. We discussed using ZZZ if a medical diversion was required. Dispatch said the Flight Attendants were talking to the POC and agreed on our diversion choices if needed. First Officer and I called up the weather; ATIS (ZZZ); reviewed the Jeppesen; and calculated our landing distances. ZZZ would be right on the line. It was very fortuitous that we did all this pre-planning; because about 20 minutes later we had to put that plan into action.All of a sudden; there was a muffled bang sound; followed by a loud whirling continuous noise like an electric motor that was failing. At the same time; there was also a small vibration that reminded me of a radar antenna motor going bad; so I immediately switched the unit off. That wasn't the problem. Next; our number 1 Flight Attendant called and said she heard a large bang by the one Right (1R) door. After she hung up; First Officer and I both thought we had a possible aircraft structural problem that may cause a rapid decompression; and we asked for a lower altitude of 14;000 feet. At this point; we knew we probably weren't going to destination.Now the noise was accompanied by an acrid electrical smell. I said let's get on oxygen and get into the smoke and fumes checklist. I handed the aircraft over to the First Officer and said tell them we want to divert to ZZZ. The number 1 called to say she smelled smoke; however when I tried to communicate with her through the oxygen mask microphone; she could not understand what I was saying. There was a loud feedback squeal in the speaker when I transmitted; and further complicating the situation; she could not understand what was being said from the poor quality of the oxygen mask microphone. After several attempts with the speaker causing a large feedback squeal; I took the mask off long enough to tell her to prepare for a landing and do a '30 second review;' I also made a quick announcement to the passengers to return to their seats; and I turned the seatbelt sign back on. It was at this time I noticed that the smoke abated but the loud humming noise continued. With the smoke subsiding; I discontinued the Smoke/Fumes Checklist after the first couple of steps. In hindsight; I should have continued beyond step 2 in the checklist; but the lack of communication distraction took me out of it until it was no longer needed.We removed our oxygen masks; briefed the approach; ran the Emergency Landing Checklist; and discussed the situation and our threats to the remainder of the flight. With the situation a little better at hand; I 'all called' the Flight Attendants and gave them a proper briefing; and said we were expecting a normal landing and taxi to the gate. I made a better; more detailed Public Address to the passengers and explained that I requested EMS to be on hand so expect to see some 'flashing lights!' We agreed that we would shoot the ZZZ ILS and leave it on the autopilot; in case the smoke started back up again. Fortunately; it did not and we successfully shot the approach; and I disconnected the Autopilot at 500 feet and got probably the smoothest landing.Once at taxi speed I made a 'remain seated 3x Public Address' and we continued to [the] gate; and deplaned using the Jetway uneventfully. Shortly after shut down while debriefing maintenance; the motor whirring noise got louder and the acrid electronics odor returned. Next; we got an ECAM 'AVIONICS SMOKE' message. I followed the QRH 'IMMEDIATE ACTION' checklist and shortly thereafter; the noise stopped; but only after the 'AV/VENT EXTRACT FAN'; circuit breaker (AC 4) popped. That concluded the evening's excitement!One final thought; First Officer related an Oxygen Mask communications procedure from a previous airline; where they would put their headsets over the oxygen mask and turn the speakers off; hence no feedback problems! I use a molded ear-piece and believe that would also work. The current procedure with the microphone/speaker feedback is unsafe and completely unacceptable!

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.