We examine the ionospheric effects of the X3.9 class solar flare occurred in the active region AR13664 of the Sun at 06:54 UT on May 10, 2024. In the course of the solar flare the X-ray and ultraviolet radiation leads to the electron density increase in D-, E-, and F region of the ionosphere causing the sudden ionospheric disturbances (SID). One of the main SID type is a short-wave fadeout (SWF). Changes in electron concentration cause alterations in ionospheric parameters and radio wave propagation conditions. We performed a detailed analysis of the behavior of the ionospheric and radio wave propagation features during SWF induced by the X3.9 class solar flare on May 10, 2024. It was found that, during SWF, an increase in the minimum frequencies fmin on vertical ionospheric sounding ionograms was observed. According to oblique ionospheric sounding data from a network of radio paths, an increase in the lowest observable frequencies and a decrease in the number of radio signal propagation modes were observed, indicating an increase in radio wave absorption. The distinctive feature of the considered event is a prolonged blackout observed by vertical and oblique ionospheric sounders.