What is indicated by the CP flag on the EHSI?

The CP flag on the Electronic Horizontal Situation Indicator (EHSI) indicates a course setting failure, which means that the selected course in the navigation system is not valid or there is an issue with the way the course has been inputted into the system. This could occur due to incorrect data entry or an internal system failure that prevents the EHSI from recognizing the selected course.

In the context of flight operations, understanding the CP flag is crucial for ensuring accurate navigation. When this flag is displayed, it alerts the pilot that the navigation information may not be reliable, prompting them to verify the course settings or switch to an alternate mode to ensure accurate navigation. This helps maintain situational awareness and safety during flight.

The other options describe different indicators or functions unrelated to course setting failures. For example, course deviation pertains to the aircraft's actual track relative to the planned route, while visibility issues would relate more to weather conditions impacting instrument readings, and navigation mode inactive indicates that the navigation system is not actively providing guidance. Each of these scenarios represents different states of navigation or system performance that do not align with the function indicated by the CP flag.