System and method for controlling dual starter air valve

A system for a gas turbine engine, comprising:

• an air turbine starter operatively coupled to the gas turbine engine and configured to rotate the gas turbine engine during a startup condition;
• a valve assembly having an airflow outlet in fluid communication with the air turbine starter, the valve assembly including:
• a first valve,
• a first valve control device coupled to the first valve and configured to control the first valve, wherein the first valve comprises a first piston, and wherein a position of the first piston is configured to control a pressure at the airflow outlet of the valve assembly;
• a second valve in fluidic series with the first valve, and
• a second valve control device coupled to the second valve and configured to control the second valve;
• a full authority digital engine control (FADEC) coupled to the valve assembly;
• a sensor configured to measure a rotational speed of the gas turbine engine;
• and
• a tangible, non-transitory memory configured to communicate with the FADEC, the tangible, non-transitory memory having instructions stored thereon that, in response to execution by the FADEC, cause the FADEC to perform operations comprising:
• receiving, by the FADEC, a rotational speed measurement from the sensor;
• determining, by the FADEC, an engine speed adjustment based on the rotational speed measurement, a position of at least one of the first valve or the second valve, and a desired speed;
• generating, by the FADEC, a command for at least one of the first valve control device or the second valve control device based on the engine speed adjustment and the desired speed;
• sending, by the FADEC, the command to at least one of the first valve control device or the second valve control device and, in response, controlling the pressure at the airflow outlet of the valve assembly to maintain the rotational speed measurement at the desired speed;
• determining, by the FADEC, a valve condition;
• and
• modulating, by the FADEC, at least one of the first valve or the second valve in response to the valve condition using pulse width modulated control to regulate the airflow through the valve assembly.