Abstract: The instant system describes a heading and attitude reference system for an aircraft in which slaving of the directional gyro to the magnetic compass and roll erection of the vertical gyro is cut off during turns which exceed a predetermined rate. A unique feature of the system is the manner in which the turn rate cutoff rate signal is generated from the directional gyro without incorporating either rate gyros or rate generators. The turn rate cutoff signal is generated from the directional gyro heading signal by converting the heading signal electrically into a signal proportional to turn rate. In one embodiment, the heading signal from the directional gyro which is representative of the heading shaft angle (.theta.) is converted into a plurality of signals proportional to the sine and cosine of shaft angle .theta.. These signals are first differentiated and then vector summed to produce a signal directly proportional to the rate of shaft rotation (d.theta.