An electronic controller for a sub-system of an air management system, the controller comprising: an area conversion module, the area conversion module comprising: an input for receiving an engine bleed output pressure set point; an input for receiving an engine bleed output pressure measurement; an input for receiving a sub-system parameter set point; an input for receiving a sub-system parameter measurement; an input for receiving a sub-system output pressure measurement, characterised by; an area set point sub-module to generate a calculated area set point output representing a restriction of flow through a sub-system, as a function of at least the engine bleed output pressure set point input, the sub-system parameter set point input, and the sub-system output pressure measurement input; and an area measurement sub-module to generate a calculated area measurement output representing a restriction of flow through a sub-system as a function of at least the engine bleed output pressure measurement input, the sub-system parameter measurement input, and the sub-system output pressure measurement input; and a sub-system area control module to generate a control output to control the sub-system, wherein the control output is a function of the area conversion module calculated area set point output and the area conversion module calculated area measurement output. an area conversion module, the area conversion module comprising: an input for receiving an engine bleed output pressure set point; an input for receiving an engine bleed output pressure measurement; an input for receiving a sub-system parameter set point; an input for receiving a sub-system parameter measurement; an input for receiving a sub-system output pressure measurement, characterised by; an area set point sub-module to generate a calculated area set point output representing a restriction of flow through a sub-system, as a function of at least the engine bleed output pressure set point input, the sub-system parameter set point input, and the sub-system output pressure measurement input; and an area measurement sub-module to generate a calculated area measurement output representing a restriction of flow through a sub-system as a function of at least the engine bleed output pressure measurement input, the sub-system parameter measurement input, and the sub-system output pressure measurement input; and an input for receiving an engine bleed output pressure set point; an input for receiving an engine bleed output pressure measurement; an input for receiving a sub-system parameter set point; an input for receiving a sub-system parameter measurement; an input for receiving a sub-system output pressure measurement, characterised by; an area set point sub-module to generate a calculated area set point output representing a restriction of flow through a sub-system, as a function of at least the engine bleed output pressure set point input, the sub-system parameter set point input, and the sub-system output pressure measurement input; and an area measurement sub-module to generate a calculated area measurement output representing a restriction of flow through a sub-system as a function of at least the engine bleed output pressure measurement input, the sub-system parameter measurement input, and the sub-system output pressure measurement input; and a sub-system area control module to generate a control output to control the sub-system, wherein the control output is a function of the area conversion module calculated area set point output and the area conversion module calculated area measurement output.