What are the two markers associated with an Instrument Landing System (ILS)?

The two markers associated with an Instrument Landing System (ILS) are the outer marker and the middle marker.

The outer marker is located approximately 4 to 7 miles from the runway threshold and provides pilots with an indication that they are approaching the final approach segment for landing. It is commonly represented by a blue light or a specific audio signal indicating the aircraft's position.

The middle marker, situated between the outer marker and the threshold, typically signals a point approximately 3,500 feet from the runway. It indicates that the aircraft is on the correct glide slope and is about to descend through the decision height for a decision to land. This marker is often associated with an amber light or a different audio tone.

Together, these markers are critical for providing pilots with visual and aural cues during the approach phase, ensuring they are aligned with the runway and maintaining the appropriate glide path for a safe landing.