Improved apparatus, systems, and methods for inspecting a structure are provided that use a probe having two ultrasonic transducer arrays. This enables simultaneous testing using two different test frequencies. The probe uses pulse echo ultrasonic signals at different frequencies to inspect the structure. The probe includes a support body having a fluid conduit formed therein. The fluid conduit provides flow paths for a couplant (such as water) that is used to couple the ultrasonic signals between the structure under test and the arrays. The fluid conduit is configured to quickly eject couplant and bubbles contained in the couplant.