The implications of binder melting and flowing on the burning surface of a heterogeneous propellant are examined phenomenologically, in the context of plateau burning behavior of certain AP composite propellants with special formulations. The effect of different diisocyanate curing agents on the melting characteristics of HTPB is observed. The effect of ambient pressure on the binder melt layer is explored by burning pure binder sandwiches. There is a qualitative indication of increased binder melt flow (a) at higher pressures, and (b) more with DDI cured HTPB than with IPDI cured HTPB. A scenario for plateau burning is presented. Increased melt flow at higher pressures causes quenching of the fine AP - binder matrix regions in the propellant via increased coverage of the fine AP particles by molten binder. The absence of the matrix flame at higher pressures dictates a reduced interaction and concomitant heat feedback by the leading edges of the diffusion flames existing over adjacent coarse AP particles, resulting in a plateau. The necessity of special propellant formulations that exhibit plateau behavior is argued based on this mechanistic hypothesis. © by S. R. Chakravarthy. E. W. Price and R. K. Sigman Published by the Americian Institute of Aeronautics and Astronautics Inc.