ILS

ILS (Instrument Landing System) is a precision radio navigation system that provides aircraft with horizontal and vertical guidance during approach and landing. It is the most widely used precision approach system in the world.

The ILS consists of two primary components:

• Localizer (LOC): Provides lateral (left/right) guidance, aligned with the runway centerline. Operates on frequencies between 108.10 and 111.95 MHz.
• Glide Slope (GS): Provides vertical (up/down) guidance, typically at a 3-degree descent angle. Operates on UHF frequencies paired with the localizer.

ILS approaches are categorized by precision level:

• CAT I: Decision height of 200 ft, visibility 550m (1,800 ft)
• CAT II: Decision height of 100 ft, visibility 300m (1,000 ft)
• CAT III: Decision height below 100 ft (or none), with varying visibility minima down to zero

ILS is being gradually supplemented by satellite-based systems like GLS (GBAS Landing System), but remains the global standard for precision approaches.