Inner marker

{
  "id": "MLC-T-AVN-000517",
  "term": "Inner marker",
  "field": "Aviation and air traffic control",
  "definition": "A marker beacon used with an ILS (CAT II) precision approach located between the middle marker and the end of the ILS runway, transmitting a radiation pattern keyed at six dots per second and indicating to the pilot, both aurally and visually, that he/she is at the designated decision height (DH), normally 100 feet above the touchdown zone elevation, on the ILS CAT II approach. It also marks progress during a CAT III approach.",
  "abbreviation": "IM",
  "synonyms": [
    "Inner marker beacon"
  ],
  "see_also": [
    "Instrument landing system (ILS)"
  ],
  "references": [
    "AIM",
    "FAA Pilot/Controller Glossary"
  ],
  "url": "https://mlchart.com/terminology/aviation/inner-marker/"
}