Unstart
![Schlieren flow visualization showing unstart of axisymmetric inlet at Mach 2. Unstarted shock structure evident on left, started inlet on right.](/Images/godic/202502/19/Inlet_shock_waves_at_Mach_21749.jpg")
In supersonic aerodynamics, unstart refers to a generally violent breakdown of the supersonic airflow. The phenomenon occurs when mass flow rate changes significantly within a duct. Avoiding unstarts is a key objective in design of the engine air intakes of supersonic aircraft.