Aircraft environmental control system including valve built-in-test without position feedback

An aircraft environmental control system (ECS) comprising:

• a first valve that is adjustable between a plurality of first positions to open or shut-off a bleed air flow that flows from an inlet of the first valve to an outlet of the first valve;
• a second valve including an inlet of the second valve in fluid communication with the outlet of the first valve, the second valve adjustable between a plurality of second positions to throttle the bleed air that flows from the inlet of the second valve to an outlet of the second valve;
• a valve position sensor coupled to the second valve and configured to output a position signal indicative of a measured position among the plurality of second positions;
• and
• an electronic hardware controller in signal communication with the valve position sensor, the controller configured to determine a primary effective area of the second valve based on the measured position, and to diagnose operation of the first valve based on the primary effective area.