Abstract: A search unit for detecting internal flaws in the web of a railroad rail includes a plastic polymer shoe having a base surface contoured to conform generally to the web surface and of sufficient width to extend substantially across the width of the web. A plurality of dual ultrasonic transducers, each transducer including a transmitter and a spaced receiver, form a linear array across the width of the shoe and are angled with respect to each other. A couplant fluid is injected between the shoe and the rail web through fluid inlets in the shoe as the unit is slid along the rail.