Disclosed is an apparatus for ultrasonic inspection of a multi-layered, ML, plate with a stiffener attached on a first surface of the ML plate. The apparatus includes a transmitter directing a first ultrasonic beam along a first guiding medium to the ML plate, along a first axis at an angle to the first surface, the first axis being within a transmission angle with respect to a first normal perpendicular to the first surface, and a receiver for receiving a transmitted ultrasonic beam originating from the first beam after passing through the ML plate along a second axis of a second guiding medium for directing the transmitted beam. The apparatus is configured for setting the transmission angle of the first axis of the first beam to let the second axis pass through a location beneath the stiffener beneath the first surface to which the stiffener is attached.