The article presents test results related to the detectability of flat discontinuities depending on their orientation in relation to the axis of an ultrasonic wave beam. A flat discontinuity used in the tests was the skew surface of a DGS standard, being an infinite reflector for an ultrasonic wave. The tests were performed using a phased array transducer and a defectoscope with a Phased Array imaging package enabling the determination of echo amplitude for various beam insertion angle values. As a result, it was possible to obtain the characteristics of a decibel echo drop depending on a beam angle of incidence on a reflector in a range from the optimum to a disadvantageous value. The article also contains the analysis of the effect of a determined characteristic on the detectability of flat discontinuities in conventional ultrasonic tests as well as discusses manners making it possible to increase the detectability of flat discontinuities. First of all, the article is addressed at NDT personnel, particularly at persons dealing with ultrasonic tests of welded joints.