A method of determining an operational state of a navigation system comprising: testing at least a portion of hardware in the navigation system (208, 324); receiving measurements of at least one navigation variable from an inertial sensor; receiving measurements of another navigation variable from an aiding source (112, 204); converting the measurements received from the inertial sensor to navigation variables equivalent to the navigation variables received from the aiding source (112, 204); combining the converted navigation variables with the navigation variables received from the aiding source (112, 204) by subtraction to determine a measurement difference value; providing the measurement difference value to a blending filter to determine a plurality of residuals for the measurement of at least one navigation variable and the measurement of another navigation variable; estimating an error for the measurement of at least one navigation variable based on the plurality of residuals; predicting an error for the measurement of at least one navigation variable while the navigation system is en route; determining whether the navigation system meets operational standards based on testing at least a portion of hardware, estimating an error for the measurement of at least one navigation variable, and predicting an error for the measurement of at least one navigation variable; and outputting one of a first state and a second state of the navigation system, the first state indicating that the navigation system does meet operational standards and the second state indicating that the navigation system does not meet operational standards. testing at least a portion of hardware in the navigation system (208, 324); receiving measurements of at least one navigation variable from an inertial sensor; receiving measurements of another navigation variable from an aiding source (112, 204); converting the measurements received from the inertial sensor to navigation variables equivalent to the navigation variables received from the aiding source (112, 204); combining the converted navigation variables with the navigation variables received from the aiding source (112, 204) by subtraction to determine a measurement difference value; providing the measurement difference value to a blending filter to determine a plurality of residuals for the measurement of at least one navigation variable and the measurement of another navigation variable; estimating an error for the measurement of at least one navigation variable based on the plurality of residuals; predicting an error for the measurement of at least one navigation variable while the navigation system is en route; determining whether the navigation system meets operational standards based on testing at least a portion of hardware, estimating an error for the measurement of at least one navigation variable, and predicting an error for the measurement of at least one navigation variable; and outputting one of a first state and a second state of the navigation system, the first state indicating that the navigation system does meet operational standards and the second state indicating that the navigation system does not meet operational standards.