These regimes are subsonic, transonic, supersonic, hypersonic, and hypervelocity flow. Transonic, supersonic, and hypersonic flows are all compressible flows. All transonic and supersonic aircraft experience Mach tuck. It also solves the issue of fluid compressibility at transonic and supersonic speeds. Aircraft designed to operate at transonic or supersonic speeds will incorporate a machmeter. The information regarding unfavourable transonic/subsonic flight behavior for some of the tested projectiles is important. The area rule concept is now used in designing all transonic and supersonic aircraft. In transonic flight, wave drag is commonly referred to as transonic compressibility drag. Most modern jet powered aircraft are engineered to operate at transonic air speeds. Severe instability can occur at transonic speeds. Aircraft flying at transonic speed often incur wave drag through the normal course of operation. This makes accurately predicting the ballistic behavior of projectiles in the transonic region very difficult. It is mission-critical for aircraft that fly through transonic Mach numbers. This is a powerful form of drag that begins at transonic speeds (around Mach 0.88). At even higher speeds (transonic), wave drag enters the picture.