Which of the following is NOT an instrument commonly used with a pressurization controller?

The landing gear indicator is not an instrument typically associated with the pressurization controller system in an aircraft. The pressurization system primarily focuses on regulating and monitoring the cabin environment to maintain comfort and safety during flight.

In contrast, the cabin altitude gauge is crucial as it displays the altitude of the aircraft's cabin, allowing monitoring of the pressurization level. The rate of climb indicator provides information on how quickly the aircraft is ascending or descending, which is important for managing cabin pressurization during changes in altitude. The cabin differential pressure gauge measures the difference between the cabin pressure and the outside atmospheric pressure, assisting flight engineers in ensuring that the cabin is properly pressurized throughout the flight.

The landing gear indicator, however, is unrelated to cabin pressurization; it serves to inform the flight crew about the status of the landing gear and is primarily connected to the aircraft's landing and taxi operations. Therefore, it does not play any role in the pressurization control system.