The numerical investigation delves into the unstart process in a hypersonic inlet-isolator model subjected to Mach 5 flow. The investigation first unravels the physics of the inlet isolators operating in the “started” mode but with different inlet compression angles ( \(\theta_{i}\) ). It is facilitated by using three inlet compression angles: \(\theta_{i} \, = \,0^{\circ}\) (no inlet compression), \(\theta_{i} \, = \,6^{\circ}\) , and \(\theta_{i} \, = \,8^{\circ}\) . The study is further extended to understand the “unstart” mode dynamics by choking the inlet-isolator with an inlet angle of \(\theta_{i} \, = \,6^{\circ}\) . It is facilitated by using a instantaneous dynamic flap operation mode at discrete angles ( \(\theta_{f}\) ) varying between \(25^{\circ} \le \theta_{i} \le 28^{\circ}\) . The initial validation of the numerical solver using the experimental data of Wagner et al. and the Large Eddy Simulation (LES) numerical data of Koo and Raman suggests the solver accurately quantifies the start and unstart dynamics associated with the isolator. The unstart shock propagation speed varies linearly with the flap angle at the exit of the isolator; however, they vary in non-linearly at locations near to the inlet region of the isolator; suggesting the flap provides a strong impact around its location.