What is the ICAO definition of "established on course"?

The correct choice, "within one dot for a LOC and within 5 degrees for an NDB," aligns with the ICAO (International Civil Aviation Organization) definition of being "established on course." This definition provides specific tolerances for different types of navigation aids which are crucial for pilots to accurately determine their position and course alignment during flight.

For a Localizer (LOC), being within one dot indicates that the aircraft is accurately tracking the course line defined by the localizer signal, ensuring precision for approaches. Similarly, for a Non-Directional Beacon (NDB), the tolerance of being within five degrees allows for a reasonable margin of error as aircraft can still effectively navigate towards the beacon while accounting for varying conditions such as wind drift and equipment limitations.

The other choices imply wider tolerances, which do not match the ICAO standards. For instance, a wider tolerance for a LOC or NDB could lead to improper course tracking, affecting flight safety and navigation accuracy, which is why the selected answer is the most precise and appropriate in this context.