The flooding phenomenon limits the stability and the flow of a liquid film falling along the walls of a tube in which a gas is flowing upwards. As is known, the entrainment effect can completely prevent the liquid fall from achieving its natural flow. Tube inclination angle has a dramatic effect on flooding velocity. The present work deals with air-water experiments carried out with a transparent circular duct test section with the aim of evaluating the influence of slight deviations from the vertical position on flooding parameters in the presence of obstructions in the channel. An improvement of the Taitel et al model for the prediction of the onset of flooding in inclined pipes is proposed.