Critical Mach number and slow down as it travels around the aircraft's structure. When the aircraft's airspeed reaches the critical Mach number, the speed of the airflow in some areas near the airframe reaches the speed of sound, even though the aircraft itself has an airspeed lower than Mach 1.0. This creates a weak shock wave. As the aircraft exceeds the critical Mach number, its drag coefficient increases suddenly, causing dramatically increased drag, and, in an aircraft not designed for transonic or supersonic speeds, changes to the airflow over the flight control surfaces lead to deterioration in control of the aircraft. In aircraft
Ford Mustang Mach 1 a cold air "snorkel" and a partial Ram Air at speed. 2004 saw only minor cosmetic changes to the Mach 1. 2004 Mach 1s can be identified by bare aluminium finished valve covers, as opposed to the 2003's black finished covers. Outside, 2004 Mach 1's wear 40th anniversary tags ahead of the doors while the 2003 has the traditional Mustang Running Pony and Tri-Color bar. The lone interior change was the deletion of the overhead "cargo net" mounted on the headliner. Despite pre-production rumors, the horsepower and torque ratings were not increased in 2004. Power rating was and . With