Airplanes have come a long way since the development of the Wright Flyer in 1903. They are now made with advanced materials like aerospace-grade aluminum and composites. Modern airplanes also boast advanced avionics, such as instrument landing systems. With an ILS, pilots no longer have to rely on visual sight when landing. What is an ILS exactly, and how does it work?
The Basics of an ILS
An ILS is an aviation system that uses radio waves to help pilots land in low-visibility conditions. It provides precise horizontal and vertical guidance. With this information, pilots can safely land in heavy fog, rain, snow or other low-visibility conditions.
How an ILS Works
Not all ILSs are the same, but most work in a similar manner. Airports are affixed with ground-based radio antennas near the runway. These antennas transmit radio signals, which are received by approaching airplanes. They provide pilots with guidance information so that they can stay aligned with the center of the runway and achieve a safe landing.
There are three main parts of a typical ILS:
- Localizer: Found at the end of the runway, the localizer is a radio antenna that sends out horizontal guidance to airplanes. It essentially tells airplanes whether they are left or right of the centerline.
- Glide slope: Found to the side of the runway, the glide slope is a radio antenna that sends out vertical guidance to airplanes. It essentially tells airplanes whether they are too high or too low.
- Distance Guidance: As the name suggests, distance guidance sends out distance information to airplanes. It tells airplanes how far away they are from the runway. For distance guidance, some airports use marker beacons — outer, middle and inner beacons — whereas others are integrated distance measuring equipment.
ILS Categories
ILSs are often categorized according to their minimum decision height. The minimum decision height is the lowest altitude at which the pilot must decide whether to land the airplane or perform a go around.
Category I ILSs have a minimum decision height of 200 feet. Category II ILSs have a minimum decision height of 100 feet. Category III ILSs have the lowest minimum decision height, with some versions allowing landings with no decision height.
In Conclusion
An ILS is a critical part of landing operations in modern airplanes. It allows pilots to approach and land safely — even when visibility is poor or nearly nonexistent. By using radio signals transmitted from antennas near the runway, ILS provides the real-time horizontal and vertical guidance needed to align with the runway and descend at the proper angle.
