Final answer:
Being established on course in aviation means that an aircraft is correctly aligned with a specific navigational signal or course line, meeting precision criteria such as within plus or minus 5 degrees for VOR/TACAN/RNAV/GPS courses, steady bearing for NDB, half-scale deflection for localizer-based courses, and often quarter-scale deflection for ICAO standards.
Step-by-step explanation:
Being "established on course" refers to the condition where an aircraft is aligned with a specific navigational signal and is tracking towards or away from a navigational aid. For a VOR/TACAN/RNAV/GPS course, this typically means the aircraft is within a prescribed number of degrees from the course centerline, usually interpreted as being within plus or minus 5 degrees of the desired track.
For an NDB (Non-Directional Beacon), being established implies keeping a steady bearing to or from the NDB station, which often requires constant adjustments due to wind and other factors. For a localizer-based course, such as that used in an ILS (Instrument Landing System), being established means being aligned with the localizer signal, generally within half-scale deflection for full precision approaches. For ICAO (International Civil Aviation Organization) standards regarding localizer-based approaches, the parameters for being established are usually tighter, often within a quarter-scale deflection to assure precise alignment with the runway centerline.