Definition
A precision approach system that guides an aircraft to a runway using two radio signals: one for lateral alignment (the localizer) and one for vertical descent path (the glide slope). Together these signals define a narrow path in space that leads the aircraft from the final approach segment down to a point near the runway threshold, allowing landings in low visibility conditions. An ILS is typically supplemented by approach lighting, marker beacons or DME for distance information, and published minimums that depend on the equipment category (CAT I, II, or III).
Plain English
A radio-based landing aid that gives the pilot two guidance signals — left/right and up/down — so the aircraft can be flown down to the runway when the pilot cannot see it until close in.
Context Anchor
Seen in instrument approach procedures, instrument training, and cockpit navigation when flying an approach to a runway in clouds or poor visibility.
Derivation
Instrument refers to flying by reference to cockpit instruments rather than outside visual cues. Landing System describes its purpose: a coordinated set of radio aids that work together to deliver the aircraft to a specific landing runway.
Why Pilots Care
It allows safe landings when weather hides the runway from view.
Grounding Statement
Picture two invisible radio beams crossing in space just above the runway: one keeps you lined up with the centerline, the other keeps you on the correct descent angle. Fly where the beams intersect and you arrive at the runway.
Intuition Check
ILS guidance does not land the aircraft by itself. It provides precise guidance; the pilot or approved aircraft equipment must still fly the approach correctly.
Example Sentence 1
Cleared for the ILS Runway 27 approach, the pilot intercepted the localizer first, then captured the glide slope and began the descent.
Example Sentence 2
With the ILS needles centered, the aircraft descended steadily toward the runway threshold.