What visibility measurement indicates conditions that affect ILS critical area access?

Visibility measurement of less than 2 miles indicates conditions that affect access to the Instrument Landing System (ILS) critical area. ILS critical areas are specific zones that must be clear of obstructions and activity to ensure the accurate operation of the ILS, particularly during low visibility situations.

When visibility drops below 2 miles, it can impact the ability of pilots and aircraft to safely navigate within the vicinity of the runway and the ILS approach. As a result, air traffic control may implement restrictions on aircraft operations within these areas to maintain safety and ensure the correct functioning of the ILS guidance. This might involve holding aircraft in a safe location or adjusting landing sequences to prevent interference with the system.

In contrast, visibility conditions of 2 miles or greater are generally considered to be more favorable for operations, allowing for smoother access to the ILS critical area without heightened risk. Therefore, the measurement of visibility being less than 2 miles specifically alerts controllers to the need for caution regarding ILS critical area access.