Improved apparatus, systems, and methods for inspecting a structure are provided that use a probe with sled appendages and an axial braking system. The probe uses pulse echo ultrasonic signals to inspect the structure. The sled appendages permit the probe to contact and ride along the surface of the structure and are rotatably connected and curved away from the surface of the structure to compensate for contoured surfaces and inspection around holes and edges. The axial braking system, in coordination with a motion control system moving the probe, fixes the positions of the sled appendages just before the probe travels over a hole or off an edge of the structure to prevent the probe from falling through the hole or off an edge and to permit the probe to return to the surface of the structure to continue inspection of the structure.