This Technical Note calls attention to the fact that observed initiation of stall in an axial flow compressor can be explained by the pressure pulses reflecting between the stator and rotor blades. The phenomenon of reflection of pressure pulses between the rotor and stator blades of turbines was first observed in in 1965 and reported in 1966. It can occur in turbines and axial- flow compressors. Subsequently the reflecting pressure pulses were able to explain turbine and axial- flow compressor blade vibrations.