Date: 202101
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Weather elements / visibility: Turbulence
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb; Cruise; Descent
Airspace: Class A ZZZ; Class E ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Interphone System
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Time Pressure; Communication Breakdown; Confusion; Distraction
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Attendant
When detected: In-flight
Result: General Maintenance Action
Contributing factors: Procedure; Weather; Aircraft
Primary problem: Aircraft

Narrative: We departed on time for a XX minute flight. Climbing through 10;000 feet I chimed the flight attendants and we continued our climb to 21;000 feet. Center was telling me to expect bad rides all the way to our destination. So when we leveled off at 21;000 feet. I made an announcement stating that the ride was going to be rough and that I would keep the seat belt sign of the entire flight. I also asked the flight attendants to remain seated for the duration of the flight as well or so I thought. The ride was not good. Continuous light occasionally moderate turbulence. The arrival is challenging on a good day and today was no exception. We were dealing with a complex arrival; turbulence; icing and multiple changes to speed and altitude. We were cleared to descend via the arrival with no speed restrictions with about a 90 knot tailwind.We would be early. Around the time that we started our descent I noticed that someone was trying to use the door code to gain access to the cockpit. I immediately declined it and made sure door was locked. The Pilot Flying and I both thought that was strange so I tried calling back to a Flight Attendant to see what was going on. That was the first indication something was wrong. When I turned on the speaker for the cabin I could hear an audible cycling noise. When I tried to chime the flight attendants I couldn't hear the chime and I could not hear any voices on the interphone. I tried to make a quick announcement but nothing was coming out back in the cabin. As the Pilot Flying and I were extremely busy managing the descent and approach we heard a knock at the door and could faintly hear a voice. Pilot Flying turned around and saw a note on the ground that said INTERPHONE INOP.I wanted to get up and grab the note to try and write something back but we were too busy. A few minutes passed. The cockpit door lock code was entered again and I denied it a second time. I tried to yell as loud as I could that we got the message. I think they must have heard that time because they stopped knocking on the door. We landed and began our taxi to the gate. After clearing the active runways I had Pilot Flying call maintenance and inform them that our Cabin Interphone and Public Address system was inoperative. We taxied to the gate and shutdown. After the shutdown checklist was complete and before the forward door was opened I got up to check on the A Flight Attendant and see if everything was OK. He was visibly upset. After the passengers got off the other two Flight Attendant's joined us up in first class to discuss what had happened. A Flight Attendant said that it was the scariest flight of his life. He said that after we had hit a rough patch of turbulence the cabin lights in the plane started to cycle on and off. They were still doing it after I went back to talk to them. He then had tried to call me to see if everything was OK but couldn't reach me. He thought that maybe we had lost pressurization and that we might have been incapacitated. He tried the door code to maybe get a peek inside to see if we were OK. He left a note under the door in hopes that we would grab it and write back. Only after the last time that he tried the door lock and I denied it did he hear me yell through the door. The other two flight attendants were also upset that they couldn't communicate with me. I spent at least 15 minutes with them trying to explain why I couldn't respond to them even though I wanted to.Trying to unlock the cockpit door without my authorization put me on high alert. This is not something I expected. If this had been a different flight with more time I would have taken their note and responded to it and sent it back. That would have been the best way. I tried yelling through the door; but it is loud in the cockpit and only on the second time did they hear me. If we had lost pressurization the masks in the back would have dropped and they would have felt it in their ears. The first time I denied his access to the cockpit door he should have known we were OK. I cannot just open the cockpit door without knowing who is behind it. My first priority is to fly the aircraft. I just didn't have enough time to respond to them the way they wanted me to.I tried to address all of their concerns and I did understand that they were upset. I wrote up the Public Address system as well as the Interphone system with their input to give the mechanics all they needed to fix the system. Maintenance came on board and reset the system. I tested the PA and both forward and aft intercoms with the Flight Attendants and in front of maintenance to make sure everything worked. Maintenance signed off the system and we than headed back. After our initial conversation about what had transpired I thought all Flight Attendants were OK just a little rattled but good enough to continue. If I had known they still had reservations about what had happened I would have immediately responded to them. My crew always comes first.


Second narrative: During our descent on the arrival we heard a knock on the cockpit door. We turned around and saw a note that was slid under the door stating that the interphone was inoperative and there were lights flashing in the cabin. We heard the Flight Attendant said that he was trying to get a hold of us. We never heard him prior to that as this was a 30 minutes or so flight and we were busy from wheels up. The Captain told him we were landing soon. When we landed Maintenance was contacted. Upon arrival at the gate the Captain met with the flight attendants to discuss the event. I went to do the walkaround. The mechanic came and fixed the problem. The interphone and Public Address system was tested before we left the gate and they worked.


Synopsis: A319 flight crew reported while experiencing turbulence they were initially unaware their PA System and interphone warnings to the cabin were not heard due to the system malfunctioning resulting in frightened and angry flight attendants.