What happens when you pass VMO/MMO?

Passing VMO (Maximum Operating Velocity) or MMO (Mach Maximum Operating Limit) indicates that the aircraft is exceeding its maximum airspeed or Mach number limits. When this limit is breached, an overspeed condition occurs, which may lead to structural damage or failure if not managed properly. The overspeed clacker—a warning sound—alerts the flight crew that the aircraft is outside of its safe operational parameters. This auditory warning is crucial for prompting immediate corrective action to return the aircraft to a safe operating speed.

In contrast, the other choices relate to different scenarios that do not directly correlate with exceeding VMO/MMO. For example, an autopilot disengagement typically occurs when the system detects manual control input or if certain flight conditions are met, not directly due to an overspeed. An aircraft entering a stall condition is related to exceeding angle of attack limits rather than airspeed. Similarly, the deployment of emergency oxygen masks is triggered by cabin pressurization failures, not by overspeed situations. Thus, the logic behind the overspeed clacker sounding serves as a clear and critical warning for pilots to address potential airspeed-related hazards.