A system for a gas turbine engine, comprising: an air turbine starter; a sensor configured to measure a rotational speed of the gas turbine engine; and 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 based on a measurement by the sensor; 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 based on the measurement by the sensor; a full authority digital engine control (FADEC) coupled to the valve assembly; 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, a position of at least one of the first valve or the second valve, a rotational engine speed, and a desired rotational engine 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 rotational engine speed; sending, by the FADEC, the command to at least one of the first valve control device or the second valve control device to control a pressure at the airflow outlet of the valve assembly to maintain the rotational engine speed at the desired rotational engine speed; determining a valve condition indicating a failure of at least one of the first valve or the second valve; and modulating, by the FADEC, at least one of the first valve or the second valve in response to the valve condition. an air turbine starter; a sensor configured to measure a rotational speed of the gas turbine engine; and 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 based on a measurement by the sensor; 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 based on the measurement by the sensor; a first valve; a first valve control device coupled to the first valve and configured to control the first valve based on a measurement by the sensor; 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 based on the measurement by the sensor; a full authority digital engine control (FADEC) coupled to the valve assembly; 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, a position of at least one of the first valve or the second valve, a rotational engine speed, and a desired rotational engine 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 rotational engine speed; sending, by the FADEC, the command to at least one of the first valve control device or the second valve control device to control a pressure at the airflow outlet of the valve assembly to maintain the rotational engine speed at the desired rotational engine speed; determining a valve condition indicating a failure of at least one of the first valve or the second valve; and modulating, by the FADEC, at least one of the first valve or the second valve in response to the valve condition. receiving, by the FADEC, a rotational speed measurement from the sensor; determining, by the FADEC, a position of at least one of the first valve or the second valve, a rotational engine speed, and a desired rotational engine 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 rotational engine speed; sending, by the FADEC, the command to at least one of the first valve control device or the second valve control device to control a pressure at the airflow outlet of the valve assembly to maintain the rotational engine speed at the desired rotational engine speed; determining a valve condition indicating a failure of at least one of the first valve or the second valve; and modulating, by the FADEC, at least one of the first valve or the second valve in response to the valve condition.