The effect of inclination angle of the downward facing flat plate on the interfacial wavy motion is investigated utilizing the water quenching test apparatus downward ebullient laminar transition apparatus flat surface (DELTA-FS) in a quasi-steady state. Film boiling heat transfer coefficients are obtained on the relatively long surface in the flow direction. Interfacial velocities at the various inclination angles and wall superheat conditions are determined through the analysis of the visualized continuous snapshots with 1000 fps. Visualization of the vapor film reveals that the interfacial wavelength increases and the interfacial velocity decreases as the flat plate moves from the vertical to downward facing locations. A new semi-empirical correlation is developed from the measured heat transfer coefficients and interfacial velocities. The correlation shows good agreement with the previous water test results on vertical plates. In the case of the previous other fluid experimental results on the vertical plates, the correlation overpredicts the film boiling heat transfer coefficients at the experimental condition.