How does a stability augmentation system (SAS) work?

SAS uses sensors (rate gyros, accelerometers) and control laws to automatically deflect control surfaces, improving stability and damping. Components: Sensors measure motion rates and accelerations, Computer processes signals through control laws (proportional, integral, derivative), Servo actuators move surfaces through authority-limited channels. Common applications: Yaw damper (reduces Dutch roll), Pitch damper (increases short period damping), Roll damper (reduces roll oscillations), and Mach trim (compensates for tuck). SAS typically has limited authority (10-15% of surface travel) and can be disconnected. It is inner-loop, automatic, while pilot provides outer-loop guidance. Essential for aircraft with marginal bare-airframe handling qualities.