Conventionally, part lives of aircraft engine components are determined by empirical and statistical analyses based on fracture mechanics or fatigue crack propagation. Advanced engine design for energy efficiency and improved performance have dictated stringent quality control of components. Small flaws can be critical to the flight safety and service life of those components. It is thus extremely important to characterize the flaw and monitor its growth for better part life management. Eddy current and fluorescent penetrant nondestructive evaluation (NDE) techniques are limited to the detection and sizing of surface cracks. Ultrasonic methods are most commonly used for detection and characterization of subsurface defects; however, some newly developed ultrasonic techniques are gaining popularity for surface flaw detection and sizing.