The localizer guides lateral alignment
Antennas beyond the far end of the runway transmit a signal that lets the aircraft determine whether it is left or right of the centerline. Pilots or autopilot systems follow that course toward touchdown.
The glide slope provides vertical guidance
A separate transmitter creates the descent path, typically around three degrees. The aircraft intercepts it from below and follows it while descending toward the runway.
Approach categories define how low the operation can continue
Category I, II and III procedures correspond to progressively lower decision heights and visibility requirements. Lower categories need more capable airport and aircraft systems.
Critical areas around the antennas must be protected
Vehicles or aircraft near the ILS transmitters can distort the signal. In low visibility, airports use special procedures to keep those areas clear.
Autoland is possible but not universal
Approved aircraft can couple autopilot systems to the ILS and perform automatic flare and rollout under certain conditions. Many ILS approaches are still hand-flown or disconnected before landing.
ILS has limitations despite its precision
Terrain, signal interference, runway geometry and maintenance requirements can constrain installation. Satellite-based approaches increasingly complement ILS rather than making it instantly obsolete.
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