The ILS identification is preceded by the letter “I” (two dots).
Each localizer facility is audibly identified by a three-letter designator transmitted at frequent regular intervals. The localizer course width is defined as the angular displacement at any point along the course between a full “fly-left” (CDI needle fully deflected to the left) and a full “fly-right” indication (CDI needle fully deflected to the right).
The localizer provides course guidance, transmitted at 108.1 to 111.95 MHz (odd tenths only), throughout the descent path to the runway threshold from a distance of 18 NM from the antenna to an altitude of 4,500 feet above the elevation of the antenna site. These are called the front and back courses, respectively. This unit radiates a field pattern, which develops a course down the centerline of the runway toward the middle markers (MMs) and outer markers (OMs) and a similar course along the runway centerline in the opposite direction.
LocalizerThe localizer (LOC) ground antenna array is located on the extended centerline of the instrument runway of an airport, located at the departure end of the runway to prevent it from being a collision hazard. For example, the compass locator may be used with NDB approaches.
These facilities may be used as a part of the ILS system, as well as part of another approach. ILS Components Ground ComponentsThe ILS uses a number of different ground facilities.
