Ultrasonic systems and methods for inspecting a channel member through a skin or panel are provided. The channel member may be a stiffener for an aircraft component such as a trapezoidal stringer attached to a skin of an aircraft fuselage. Transducers of the system are disposed on a side of the skin opposite the channel member. Ultrasonic waves generated on a first side of a skin propagate through the skin, across a channel member attached to a second side of the skin, and through the skin again to be received on the first side of the skin. Times of flight are measured for the collection of time-gated data. A two dimensional C-scan is generated for identifying flaws and irregularities in a structure by way of single-side ultrasonic non-destructive inspection (NDI).