Which statement accurately describes the relationship between the cabin pressure controller and the altitude regulator?

• A. The cabin pressure controller varies cabin altitude; the altitude regulator limits the maximum altitude.
• B. The altitude regulator varies cabin altitude; the cabin pressure controller limits the maximum altitude.
• C. Both regulate the same parameter.
• D. Neither has any effect.

Answer: (A)

In the Beechjet 400A pressurization system, the cabin pressure controller actively maintains the cabin altitude by modulating the outflow valve to reach and hold the commanded setpoint from the altitude selector. The altitude regulator, meanwhile, acts as a safety limit, preventing the cabin altitude (and thus the differential pressure) from exceeding a maximum value. So the controller is responsible for varying cabin altitude, while the altitude regulator provides a ceiling to how high the cabin altitude can climb. The other descriptions don’t fit because the regulator’s role is not to vary cabin altitude, and the two components do not regulate the same parameter.