1 0 1 2 3 5 6 9 10 8 CABIN ALT RATE B A R C O R CABIN PRESSURE CONTROL Rate selector knob Cabin altitude selector knob (selects isobaric setting) Barometric pressure correction knob Barometric pressure indicator Indicates maximum altitude before differential operation Cabin pressure  selector DECR INCR DOWN UP > 35° 28VDC < 35° Takeoff throttle switches > 35° < 35° LEFT RIGHT Mode switch Electropneumatic control valve (torque motor) Primary outflow valve Secondary outflow valve Cabin pressure test port Static port Static port AFT pressure bulkhead Slave line Altitude limiter Altitude limiter Pneumatic relay 28 VDC from battery bus Auto Manual Jet pump vacuum source 28VDC Normal Emergency depress switch Emergency 28VDC Manual regulator Cabin press relay (energized  with wow) Landing gear control unit 28VDC Up Down Cabin pressure  sense port Air pressure  regulating valve Static pressure source Cabin Atmosphere −1 0 1 3 4 5 6 7 10 9 8 2 LAG ALT x 1000 FT. BARO IN. HG 31 30 29 28 27 INCR FAULT R A B 16-30 Figure 16-52.  The pressurization control system on many small transports and business jets utilizes a combination of electronic, electric,  and pneumatic control elements.  Figure 16-51.  A pressure controller for an all pneumatic cabin  pressure control system.  Modern aircraft often combine pneumatic, electric, and  electronic control of pressurization. Cabin altitude, cabin  On many transport category aircraft, two cabin pressure  controllers, or a single controller with redundant circuitry, are  used. Located in the electronics equipment bay, they receive  electric input from the panel selector, as well as ambient  and cabin pressure input. Flight altitude and landing field  altitude information are often the crew selection choices on  the pressurization control panel. Cabin altitude, rate of climb,  and barometric setting are automatic through built-in logic  and communication with the ADC and the flight management  Using this information, the controller, which is essentially  a computer, supplies pressurization logic for various stages  of a flight. On many small transport and business jets, the  controller’s electric output signal drives a torque motor in  the primary outflow valve. This modulates pneumatic airflow  through the valve, which positions the valve to maintain the  pressurization schedule.  rate of change, and barometric setting are made on the cabin  pressure selector of the pressurization panel in the cockpit.  Electric signals are sent from the selector to the cabin pressure  controller, which functions as the pressure regulator. It is  remotely located out of sight near the cockpit but inside the  pressurized portion of the aircraft. The signals are converted  from electric to digital and are used by the controller. Cabin  pressure and ambient pressure are also input to the controller,  as well as other inputs.  [Figure 16-52]