Narrative:

During climbout on the departure from ZZZ at about 22;000 feet we received the master caution light/chime in addition to numerous EICAS messages. The autopilot disengaged as well as the auto-throttles. Since I was the pilot flying my first reaction was to inform the pm (pilot monitoring) that 'I had the airplane' and we silenced the autopilot and auto-throttle warnings as well as the chiming. I transferred controls to the first officer (first officer) while I performed the QRH procedure associated with the main EICAS message 'avnx mau 3A fail.' there were numerous other EICAS messages associated with the failure that were highlighted in the QRH; such as inoperative multifunction spoilers; speed brakes; APU; rh aileron indication; FMS 2 etc. The QRH directed the crew to land as soon as practical. Since we were close to ZZZ and the weather was great it made the most suitable airport and we decided to return. We [requested priority handling] with ATC and requested vectors back to ZZZ to join the ILS runway xxl and for [crash fire rescue equipment] on standby. Due to the busy nature of the situation and because were now being descended and vectored back to ZZZ I asked ATC to inform compass as I did not have time to call them on [handheld] radio or arinc. I also sent a brief message to dispatch to let them know we were returning. We were unaware to what degree of control we would have due to the inoperative spoilers; speed brakes; brake fault; and other system degradations so we requested a wider base pattern and slowed earlier to ensure a stable flaps full approach as directed by the QRH. Due to a brake fault message; among other issues; we decided it would be safest to come to a stop on the runway and be towed off. We shut down the engines for the tow off the runway and due to the inoperative APU associated with the mau 3A fail we were only on battery power to the gate.once we had arrived at the gate and the passengers were safely deplaned into the terminal there was rush of people. [Company] mechanics was already there in addition to numerous customer service agents and ramp agents. It was then that I called dispatch to carry forward with the process and talk to maintenance and the on-duty chief pilot.instead of transferring me to the on-duty chief pilot; dispatch instead started to question my PIC decision to do an air return as the safest option. Dispatch asked me how far was I into the flight distance wise and started telling me their interpretation of the QRH procedure. I informed the dispatcher that I would not be arguing with him on my decision to do an air return and demanded to speak with the on duty chief pilot.I was handed over the chief pilot and informed him of the issue that caused the return. The chief pilot asked me a few short questions and requested a crew report. Simultaneously to all this my first officer had grabbed my bags due [company] maintenance and ramp operations wanting to get the aircraft off the gate and towed to hanger because they wanted the gate space for an inbound flight. During this busy time I was distracted and was not able to write up the deferral in the maintenance logbook. After talking to maintenance on the phone after the fact; I was able to tell them the issue and I was told the discrepancy had been written up and a work order had been generated.the dispatcher was attacking and questioning my decision based on his own interpretation. I did not feel that dispatch was putting safety as the priority.2

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Original NASA ASRS Text

Title: EMB-175 flight crew reported loss of MAU-3 on climbout; requiring an air turn back and a priority landing.

Narrative: During climbout on the departure from ZZZ at about 22;000 feet we received the master caution light/chime in addition to numerous EICAS messages. The autopilot disengaged as well as the auto-throttles. Since I was the pilot flying my first reaction was to inform the PM (Pilot Monitoring) that 'I had the airplane' and we silenced the autopilot and auto-throttle warnings as well as the chiming. I transferred controls to the FO (First Officer) while I performed the QRH procedure associated with the main EICAS message 'AVNX MAU 3A FAIL.' There were numerous other EICAS messages associated with the failure that were highlighted in the QRH; such as inoperative multifunction spoilers; speed brakes; APU; RH aileron indication; FMS 2 etc. The QRH directed the crew to land as soon as practical. Since we were close to ZZZ and the weather was great it made the most suitable airport and we decided to return. We [Requested Priority Handling] with ATC and requested vectors back to ZZZ to join the ILS Runway XXL and for [Crash Fire Rescue Equipment] on standby. Due to the busy nature of the situation and because were now being descended and vectored back to ZZZ I asked ATC to inform compass as I did not have time to call them on [Handheld] radio or ARINC. I also sent a brief message to Dispatch to let them know we were returning. We were unaware to what degree of control we would have due to the inoperative spoilers; speed brakes; brake fault; and other system degradations so we requested a wider base pattern and slowed earlier to ensure a stable flaps full approach as directed by the QRH. Due to a brake fault message; among other issues; we decided it would be safest to come to a stop on the runway and be towed off. We shut down the engines for the tow off the runway and due to the inoperative APU associated with the MAU 3A fail we were only on battery power to the gate.Once we had arrived at the gate and the passengers were safely deplaned into the terminal there was rush of people. [Company] Mechanics was already there in addition to numerous customer service agents and ramp agents. It was then that I called Dispatch to carry forward with the process and talk to Maintenance and the on-duty Chief Pilot.Instead of transferring me to the on-duty Chief Pilot; Dispatch instead started to question my PIC decision to do an air return as the safest option. Dispatch asked me how far was I into the flight distance wise and started telling me their interpretation of the QRH procedure. I informed the Dispatcher that I would not be arguing with him on my decision to do an air return and demanded to speak with the on duty Chief Pilot.I was handed over the Chief Pilot and informed him of the issue that caused the return. The Chief Pilot asked me a few short questions and requested a crew report. Simultaneously to all this my First Officer had grabbed my bags due [Company] Maintenance and ramp operations wanting to get the aircraft off the gate and towed to hanger because they wanted the gate space for an inbound flight. During this busy time I was distracted and was not able to write up the deferral in the maintenance logbook. After talking to Maintenance on the phone after the fact; I was able to tell them the issue and I was told the discrepancy had been written up and a work order had been generated.The Dispatcher was attacking and questioning my decision based on his own interpretation. I did not feel that Dispatch was putting safety as the priority.2

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.