Which control switch regulates the position of the bi-level control and shutoff valve?

The correct answer involves the "Bleed air inflow" control switch, which is responsible for regulating the position of the bi-level control and shutoff valve. In the T-6B aircraft, the bleed air system is essential for managing various environmental and pneumatic functions. The flow of bleed air is utilized for cabin pressurization, temperature control, and other vital systems.

By controlling the bleed air inflow, the pilot can effectively manage how air is supplied to the environmental control system and ensure that the valve positions are appropriate for maintaining the desired cabin conditions. The bi-level control valve is specifically designed to regulate this airflow and maintain the required temperature and pressure levels within the cockpit and cabin.

Other options relate to separate functions: the pressurization switch manages the overall cabin pressure but not directly the bi-level control valve; the ram air flow pertains primarily to outside airflow entering the aircraft, affecting different systems; and the air conditioner switch controls the functionality of the air conditioning unit but does not directly influence the positioning of the bi-level control valve. Understanding these distinctions is key to grasping the integrated nature of the aircraft's systems.