What is the purpose of marker beacon systems and what are OM, MM, IM?

• A. They measure air pressure to determine altitude.
• B. They provide approach-position cues including Outer Marker, Middle Marker, and Inner Marker with audio/visual cues.
• C. They monitor cabin air quality during flight.
• D. They transmit weather data to the cockpit.

Answer: (B)

Marker beacon systems provide approach-position cues along an ILS, giving you a precise sense of where you are on the final approach through both sound and light indicators. As you fly the approach, you may pass three marker positions: the Outer Marker, the Middle Marker, and the Inner Marker. Each has its own distinctive cue to tell you where you are along the approach path.

The Outer Marker sits farther out on the final approach and is associated with a blue cockpit light and a specific audio tone. It signals that you’ve intercepted and are established on the published approach path, typically well before you reach the runway area. The Middle Marker is placed closer to the runway and uses an amber light with a different tone, giving you a mid-approach reference. The Inner Marker, used mainly for very low-visibility precision approaches, is located near the threshold or decision point and uses a white light with yet another tone, marking the final portion of the approach.

Each marker’s tone and light combination helps you identify exactly which marker you’re crossing, providing a redundant, easy-to-interpret cue in instrument conditions. Marker beacons operate at a fixed frequency and are part of traditional ILS guidance, though many newer systems rely more on other navigation aids; their role is to give clear, immediate situational awareness about position relative to the runway.