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What is VOR/MB in Aviation? (Vor Marker Beacon)

Updated: March 13, 2024

What is a VOR Marker Beacon (VOR/MB)?
A VOR Marker Beacon (VOR/MB) is a navigation aid used in aviation to provide pilots with accurate position information during instrument approaches. It is a ground-based radio transmitter that emits signals that can be received by aircraft equipped with the necessary VOR/MB receivers. The VOR/MB system consists of three different types of beacons, each providing a specific type of information to the pilots.

VOR/MB Types
There are three types of VOR/MB beacons: the Outer Marker (OM), the Middle Marker (MM), and the Inner Marker (IM). Each marker beacon is located at a specific distance from the runway threshold and provides different indications to the pilot, helping them determine their position during an instrument approach.

Outer Marker (OM)
The Outer Marker (OM) is the first marker beacon encountered by an aircraft during an instrument approach. It is typically located 4 to 7 nautical miles from the runway threshold. When the aircraft approaches the OM, the VOR/MB receiver on board detects the signal and alerts the pilot. The OM is identified by a blue light on the aircraft's instrument panel and an aural tone in the cockpit. This indication tells the pilot that they are approximately 1 to 3 nautical miles from the runway threshold.

The Outer Marker is a crucial point during an instrument approach as it serves as a reference to begin the descent towards the runway. At this point, the pilot should have established the required descent profile and be prepared to transition from instrument flight to visual flight when the runway is in sight. The OM provides an additional layer of safety by ensuring that the aircraft is at the correct altitude and position before continuing the approach.

Middle Marker (MM)
The Middle Marker (MM) is the second marker beacon encountered by the aircraft during an instrument approach. It is typically located 0.5 to 0.9 nautical miles from the runway threshold. Similar to the Outer Marker, the MM emits a specific signal that triggers the VOR/MB receiver on board the aircraft.

When the MM signal is received, the VOR/MB receiver activates an aural tone and illuminates an amber light on the instrument panel. This indication informs the pilot that they are approximately 0.2 to 0.4 nautical miles from the runway threshold, providing a final check before the aircraft reaches the decision height (DH) or minimum descent altitude (MDA).

The Middle Marker is a critical point during an instrument approach as it serves as the final check for the pilot before transitioning to a visual landing. It ensures that the aircraft is at the correct altitude and position for a safe descent and landing.

Inner Marker (IM)
The Inner Marker (IM) is the last marker beacon encountered during an instrument approach. It is typically located around 0.1 nautical miles from the runway threshold. Like the Outer and Middle Markers, the IM emits a specific signal that triggers the VOR/MB receiver on board the aircraft.

When the IM signal is received, the VOR/MB receiver activates a different aural tone and illuminates a white light on the instrument panel. This indication informs the pilot that they are approximately 0.05 nautical miles from the runway threshold, providing the final confirmation before touchdown.

The Inner Marker is a crucial point during an instrument approach as it serves as the last reference for the pilot before touchdown. It ensures that the aircraft is at the correct altitude and position for a safe landing. Once the Inner Marker is crossed, the pilot can discontinue relying solely on instruments and transition to visual cues for a smooth touchdown.

In conclusion, VOR Marker Beacons (VOR/MBs) play a vital role in aviation by providing pilots with accurate position information during instrument approaches. The Outer, Middle, and Inner Markers serve as reference points, helping pilots determine their position relative to the runway threshold. These marker beacons enhance safety and situational awareness, allowing for precise navigation and smooth landings. Pilots rely on the indications provided by the VOR/MB system to ensure a safe and successful instrument approach.

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