Subsonic flow occurs when the speed of the fluid (typically air) is less than the speed of sound—that is, it has a Mach number less than 1. In subsonic conditions, compressibility effects are usually minimal, especially at lower speeds (below Mach 0.3), and the flow tends to behave smoothly. Changes in pressure, temperature, and density occur gradually. This type of flow is typical for most commercial aircraft and general aviation planes. Supersonic flow, on the other hand, happens when the fluid moves faster than the speed of sound, meaning the Mach number is greater than 1. At these speeds, compressibility effects become very significant. Supersonic flow involves sudden changes in flow properties such as pressure and temperature, often marked by the presence of shock waves. These are abrupt transitions in the flow caused by the inability of pressure disturbances to travel upstream. Supersonic flow is typical of fighter jets, missiles, and high-speed aerospace vehicles