Ultrasonic guided waves are used for the detection of hidden corrosion in such aircraft components as helicopter blades, landing gears, multi-layer components, tear strap and lap splice joints, helicopter transmission beams, and skin to core debonding in honeycomb structures. A new technique of phase velocity and frequency tuning is introduced for optimizing the defect detection process. Key Words: Ultrasonics, guided waves, corrosion detection, aircraft inspection, nondestructive evaluation