If the EHSI course indication cannot be changed, what indication might confirm this issue?

The CP flag, or Course Pointer flag, is an indication that alerts the pilot to an issue with the course setting on the Electronic Horizontal Situation Indicator (EHSI). When this flag is displayed, it typically means that the course indication cannot be changed or is invalid. This scenario might arise due to a malfunction in the navigation systems, indicating that the system is not receiving valid data or that there is a failure in computing the necessary information to adjust the course pointer.

In the context of other flags, each serves different functions related to navigation and aircraft positioning. The HDG flag alerts the pilot to a problem with the heading indicator; the ILS flag refers to issues with the Instrument Landing System, and the DME flag indicates a failure in the Distance Measuring Equipment. While these flags provide critical information regarding their respective systems, the CP flag specifically signifies a fault concerning the course indication of the EHSI, making it the correct indication to confirm the issue of an unchangeable course indication.