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The behavior of the disturbance waves is studied in downward adiabatic air-water annular flow in a vertical pipe with an inner diameter of 11.7 mm. The range of liquid wetting densities is 2.5–4.6 cm²/s and the range of superficial gas velocities is 22–57 m/s. The paper is focused on the downstream evolution of the main properties of individual disturbance waves at the stage of flow development along with the process of coalescence of disturbance waves. Brightness-based laser-induced fluorescence technique enabled us to obtain spatiotemporal matrices of the local instantaneous thickness of liquid film along one longitudinal section of the pipe with a length of 400 mm. Dependencies of the main characteristics of the flow on the downstream distance are analyzed. Local shear stress, base film thickness, and longitudinal size of the disturbance waves are stabilized at the distance of 150–200 mm below the inlet …