From where does the pressurization controller normally use landing elevation QNH?

The pressurization controller on the A320 typically utilizes the landing elevation QNH information from the Flight Management and Guidance Computer (FMGC). The FMGC serves as the central point for managing flight data, including navigation and performance parameters, which encompasses the handling of pressure settings for cabin pressurization.

The reason this is the correct choice is that the FMGC is programmed to accept data regarding the airport's elevation and corresponding QNH settings, which are critical for accurately adjusting the cabin pressure before landing. This allows the airplane to maintain a safe environment for passengers and crew, as it prepares for descent and landing.

While other components such as the ADIRUs and the captain's barometric altimeter provide important data, they are not primarily responsible for the pressurization control system's functions. The LDG ELEV Selector, on the other hand, is specifically for the selection of landing elevation, but it does not itself provide the QNH data that the FMGC processes for pressurization control.