Under what condition are Category II approaches prohibited?

Category II approaches are typically used when pilots need to land in low visibility conditions, so the criteria surrounding their use are quite specific. The condition that prohibits Category II approaches is when the braking action is reported as less than MEDIUM. This is crucial because low braking action can severely impact the safety of the landing, especially in poor weather conditions that Category II approaches are designed to handle.

If the braking action is less than MEDIUM, it indicates that the runway conditions could significantly impair the aircraft's ability to decelerate after landing. This poses a risk for runway overruns or difficulties maneuvering the aircraft on the runway, thereby making the approach unsafe regardless of other factors like visibility or equipment capabilities.

The other conditions listed, such as visibility being below minimums or the aircraft lacking autoland capability, could also restrict certain types of approaches but do not specifically relate to the safety concerns associated with runway braking conditions during a Category II landing.