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Disturbance waves are complex three-dimensional large-scale structures appearing on liquid films under strong gas shear. They strongly intensify heat, mass and momentum interchange between the phases, thus affecting the efficiency of industrial equipment. Here we analyze inception and three-dimensional spatiotemporal evolution of disturbance waves on a gas-sheared liquid film flowing along the bottom of a wide horizontal duct. The experiments are carried out using Brightness-Based Laser-Induced Fluorescence technique in a large region of interrogation with length of 380 mm and width of 166 mm (equal to the width of the duct). The range of gas superficial velocities is from 6 to 24 m/s with a step of 2 m/s; the range of liquid wetting densities is from 1 to 8 cm²/s with a step of 1 cm²/s. Three working liquids with different viscosity and surface tension are employed. Transition from small-scale 3D-waves to …