Also found in: Acronyms.
outer marker[′au̇d·ər ′mär·kər]
That instrument landing system (ILS) marker farthest from the approach end of the instrument runway; the marker is located 4.5 miles ± 1000 feet (7240 ± 305 meters) from the end of the runway and not more than 250 feet (75 meters) from the extended center line of the runway.
An ILS (instrument landing system) navigational facility in the terminal area navigation system located at 4 to 7 miles (6 to 11 km) from the runway edge on the extended centerline. It transmits a 75-MHz fan-shaped radiation pattern, modulated at 400 Hz (fan markers and station markers radiate at 3000 Hz, whereas middle markers do so at 1300 Hz), keyed at two dashes per second, and received by compatible airborne equipment. It indicates to the pilot, both aurally and visually, that he or she is passing over the facility and can begin the final approach. See instrument landing system.