How are fly-by-wire flight control laws designed and validated?

Flight control law design achieves desired handling qualities while ensuring stability and protection. Process: Define handling qualities requirements (MIL-STD-1797, Cooper-Harper ratings), Develop mathematical model of aircraft dynamics, Design control laws using classical (PID), modern (H-infinity, LQR), or robust control methods, Implement envelope protections (AOA limiting, load factor, speed). Modes: Normal law (full protection), Alternate law (reduced protection), and Direct law (basic control). Validation: Piloted simulation (handling qualities assessment), Non-real-time simulation (coverage of flight envelope), Robustness analysis (stability margins across uncertainties), and Flight test (envelope expansion, pilot evaluation). Certification requires demonstrating stability, controllability, and protection throughout flight envelope with single/multiple failures. Extensive failure mode testing in simulation and flight.