Description (AMM 21-31-00)

 

A- The pressure controller is an electronic unit which receives inputs from the pressurization control panel, airplane ambient pressure and cabin pressure, then positions the outflow valve to maintain proper differential pressure.

 

B- Two completely independent pressure control system networks are contained within the pressure controller. The automatic system operates as a function of destination landing field altitude and cruise altitude while the standby system operates according to the selected cabin altitude and selected rate of cabin pressure change.

 

C- Inputs to the pressure controller for the automatic and standby systems are shown schematically on a block diagram.

 

D- All outputs from the pressure controller operate the cabin pressurization outflow valve. The controller will operate either under the automatic system or the standby system, but never the two systems simultaneously.

 

The FLT-GRD switch is used to modify the two outputs for cabin pressurization control on the ground. When the switch is moved to FLT position with the mode selector in AUTO the valve will move to a position which will cause cabin pressure to rise slightly above (approximately 0.1 psi) that of the takeoff field. With the selector in STBY the valve will be positioned to control the pressure to the selected standby cabin altitude.

 

With mode selector switch in either AUTO or STBY and FLT-GRD switch is moved to GRD (airplane on ground), the outflow valve will move to the full open position at the rate necessary to completely depressurize the airplane at rate limit.

 

E- On the front of the controller, there are test points under a cover which are used for trouble-shooting the pressurization control system. On the rear of the controller, the upper connection is used only for bench test.

 

F- The pressure controller is installed in the electronic equipment compartment on the forward top shelf. There is a delta P module installed adjacent to the pressure controller, which supplies a maximum of 7.45 psi with the pressurization mode selector in AUTO and 28,000 ft or below selected with the FLT ALT selector. A 7.80 À P is supplied when FLT ALT above 28,000 ft is selected with the pressurization mode selector in AUTO. STANDBY maximum pressure differential is 7.8 psi.