How are Instrument Landing System (ILS) critical areas marked?

Instrument Landing System (ILS) critical areas are marked with red markings. This is essential for maintaining the integrity of the ILS signals, which guide aircraft during the final approach and landing phases. The red markings indicate areas that must remain clear to ensure that the precise signals used for navigation are not disrupted by vehicles or personnel.

By using red markings, the area is easily recognizable to pilots and ground personnel, emphasizing the importance of these zones in airport operations. This helps prevent any interference that could affect the safety and precision of an aircraft landing, particularly in low visibility conditions when the ILS is most critical.

The other options, such as yellow markings, blue lights, and green surfaces, are used in different contexts throughout airport operations, but they do not indicate ILS critical areas specifically. Yellow markings are often associated with taxiway boundaries, blue lights are typically used for identifying service roads and safety areas, while green surfaces may denote taxiways or other operational areas, but none of these serve to highlight the critical nature of ILS zones.