An apparatus for detecting defects in a railway rail includes a search unit and preferably a roller search unit (“RSU”) mounted on a test vehicle and in rolling contact with the running surface of the rails to inspect each rail. The RSU includes a tire filled with a liquid and a transducer assembly mounted within the tire. The transducer assembly includes one or more arrays of ultrasonic transducers directed toward the running surface of the rail. A laser profiler mounted on the test vehicle in combination with a linear encoder provide profile data which is communicated to a system controller to dynamically adjust the focal laws for the one or more arrays of transducers to dynamically steer the transmitted beams to produce the ideal inspection beam sets while the test vehicle is in motion.