Final answer:
To enter HVR mode, the airspeed of the aircraft must be below a certain critical Mach number, which is the speed at which the airflow over certain parts of the aircraft reaches the speed of sound. The specific airspeed required to enter HVR mode depends on the aircraft and other factors. For many commercial airliners, the critical Mach number is around 0.8-0.85, corresponding to an airspeed of approximately 525-575 knots (606-663 mph, 978-1063 km/h) at cruising altitudes.
Step-by-step explanation:
In order to enter HVR (High-Velocity Regime) mode, the aircraft must be below a certain airspeed. The specific airspeed required to enter HVR mode will depend on the aircraft and other factors, but generally, it is at or above the critical Mach number. The critical Mach number is the airspeed at which the airflow over certain parts of the aircraft, such as the wings, reaches the speed of sound. When the aircraft exceeds the critical Mach number, shock waves form and cause a significant increase in drag and other aerodynamic effects.
For example, many commercial airliners have a critical Mach number around 0.8-0.85, which corresponds to an airspeed of approximately 525-575 knots (606-663 mph, 978-1063 km/h) at typical cruising altitudes. So, to enter HVR mode, the airspeed would need to be below this threshold.