What is the spacing between the parallel lines in ILS holding position markings?

The spacing between the parallel lines in Instrument Landing System (ILS) holding position markings is established to ensure clear visual guidance for pilots and ground personnel. The correct spacing of 4 feet is designed to be unambiguous and consistent with the standard markings used at airports, which helps in the safe navigation of aircraft near runways and taxiways. This distance facilitates better visibility and demarcation of critical areas, ensuring that pilots adhere to operational procedures while waiting for clearance to enter active runways. Having a standardized spacing like this is crucial for maintaining safety and operational integrity at busy airports such as O’Hare.