Which function does the outflow valve primarily serve in AUTO mode?

The outflow valve primarily serves the critical function of controlling cabin differential pressure in AUTO mode. This valve is essential for maintaining a safe and comfortable environment inside the aircraft by regulating the pressure difference between the cabin and the outside atmosphere as the aircraft ascends and descends.

When operating in AUTO mode, the outflow valve automatically adjusts its position to achieve the desired cabin pressure in accordance with the flight profile. It plays a pivotal role in managing the cabin altitude, ensuring that it remains within the limits for passenger and crew comfort and safety. This automatic regulation adjusts the outflow of air from the cabin to match the inflow of air, thereby stabilizing differential pressure.

While other options might relate to relevant systems within the aircraft's pressurization setup, they do not perform the primary function of managing the cabin's pressure. The safety valve is not adjusted by the outflow valve, nor do inlet and extract valves directly interact with the outflow valve's main duty of pressure control.