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Aviation glossary

ILS

Instrument Landing System · Also: instrument landing system, ILS approach

Airports

Ground-based radio guidance system that leads an aircraft both laterally and vertically to the runway, allowing landings in very poor visibility.

What it is

The ILS combines two radio beams. The localiser, whose antennas stand beyond the far end of the runway, shows whether the aircraft is left or right of the centreline. The glideslope, located beside the touchdown zone, defines a descending path that is typically 3 degrees. Many installations are complemented by distance measuring equipment (DME) or marker beacons that identify fixed points on the approach.

Cockpit instruments display the deviation from both beams, and the autopilot can follow them very precisely. It is a precision approach: the pilot descends to a decision height and continues only if the runway's visual references are in sight. Depending on airport equipment, aircraft certification and crew training, ILS operations are divided into categories that allow aircraft to descend lower before seeing the runway.

Related terms

ILS categoriesClassification of ILS approaches by minimum decision height and visibility, from CAT I to CAT III, which allows aircraft to land in dense fog. ApproachThe phase of flight in which the aircraft lines up with the runway and descends along a defined path to the point where the crew decides to land or go around. VORGround-based radio aid transmitting on VHF that lets an aircraft determine which radial, or magnetic bearing from the station, it is on. AutopilotSystem that holds or changes an aircraft's flight path, altitude, heading and vertical speed according to values selected by the crew. LandingThe final phase of flight in which the aircraft crosses the runway threshold, touches down on its main gear and slows to taxi speed.
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This page was last updated on October 9, 2026

APA

Vuelopedia. (2026, October 9). ILS. Retrieved October 17, 2026, from https://vuelopedia.org/en/glossary/ils

MLA

“ILS.” Vuelopedia, Fundación Poderia, 9 Oct. 2026, vuelopedia.org/en/glossary/ils. Accessed 17 Oct. 2026.

Chicago

Vuelopedia. “ILS.” Fundación Poderia. Last modified October 9, 2026. https://vuelopedia.org/en/glossary/ils.

Harvard

Vuelopedia (2026) ILS. Available at: https://vuelopedia.org/en/glossary/ils (Accessed: 17 October 2026).

BibTeX

@misc{vuelopedia_en_glossary_ils,
  author       = {{Vuelopedia}},
  title        = {{ILS}},
  publisher    = {Fundación Poderia},
  year         = {2026},
  date         = {2026-10-09},
  url          = {https://vuelopedia.org/en/glossary/ils},
  howpublished = {\url{https://vuelopedia.org/en/glossary/ils}},
  urldate      = {2026-10-17},
  note         = {Accessed 2026-10-17}
}

Wikipedia

{{cite web |url=https://vuelopedia.org/en/glossary/ils |title=ILS |website=Vuelopedia |publisher=Fundación Poderia |date=2026-10-09 |access-date=2026-10-17 |language=en}}

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