ILSs

Instruction Landing Systems (ILSs) are ground‑based radio navigation aids used in aviation to provide precision guidance to aircraft during the final approach phase to an airport runway. Each ILS consists of two main components: the localizer, which supplies lateral guidance by transmitting a signal that represents the aircraft’s position relative to the centerline of the runway, and the glideslope transmitter, which provides vertical guidance by indicating the optimal descent angle. Together, these signals allow pilots to align their aircraft with the runway and maintain the correct glide path, even in low‑visibility conditions.

ILSs are classified by the recommendations of the International Civil Aviation Organization (ICAO). Types are designated as A, B, C, or D based on the required instrument approach category (i.e., the minimum visibility levels and glide angle). Category I allows a decision height of 200 feet and a runway visual range (RVR) of at least 550 meters. Category II requires a decision height of 100 feet and an RVR of 300 meters, while Category III permits landings with no decision height or even zero visibility, depending on the sub‑category (IIIa, IIIb, IIIc).

Instrumentation groups, which are installed and maintained by the state aviation authority, are responsible for ensuring the reliability and accuracy of ILSs. Routine calibration checks, component replacements, and performance monitoring are essential for maintaining safety standards. Modern aircraft are equipped with multicore navigation displays that automatically select the most appropriate ILS approach based on aircraft type and runway configuration. Although newer satellite‑based augmentation systems can provide comparable precision, ILSs remain a critical infrastructure for worldwide approach and landing procedures.