Instrument Landing System
A ground-based precision approach system that provides lateral and vertical guidance to aircraft on final approach, independent of GPS or any satellite signal.
What is ILS?
The Instrument Landing System (ILS) is a ground-based radio navigation system that guides aircraft to a runway in poor visibility conditions. It consists of two components: the localizer (providing lateral guidance to the runway centerline) and the glide slope (providing vertical descent guidance at typically 3 degrees). ILS operates on dedicated VHF/UHF frequencies entirely independent of GPS, making it immune to satellite-based interference.
Before GPS became widespread, ILS was the primary precision approach system worldwide. As aviation moved toward satellite-based navigation (RNAV/RNP approaches), some airports decommissioned ILS equipment, viewing it as legacy infrastructure. The GPS interference crisis of 2023-2025 reversed this trend dramatically. Airports in GPS-denied environments — particularly Beirut, where persistent spoofing and jamming have affected GPS approaches since 2023 — have come to rely entirely on ILS as the only viable precision approach method.
EASA and several national authorities have now reversed plans to decommission ILS at major airports, recognizing that ground-based navigation backup is essential in an era of electronic warfare. Airports without maintained ILS infrastructure face a critical vulnerability: if GPS is denied, they may have no precision approach capability at all, potentially forcing closures during interference events.
Why It Matters for Airspace Risk
ILS availability determines whether an airport can continue operations during GPS interference events. Airports with maintained ILS can accept traffic even under heavy jamming or spoofing; those without it may become effectively closed. FlySafe assesses airport resilience based partly on ground-based navigation backup — ILS availability is a key factor in determining whether GPS interference in a region will cause full operational disruption or merely degrade efficiency.
Key Facts
- •ILS operates on VHF (108-112 MHz localizer) and UHF (329-335 MHz glide slope), completely independent of GNSS satellites.
- •Beirut-Rafic Hariri International Airport has relied primarily on ILS approaches since persistent GPS interference began in 2023.
- •ILS Category III systems allow landings in near-zero visibility (as low as 50ft decision height / 200m runway visual range).
- •Several European aviation authorities reversed ILS decommissioning plans in 2024-2025 following the GPS interference surge.
Related Terms
Related Case Studies
This definition is for informational purposes. Always consult official ICAO/EASA/FAA documentation for regulatory definitions.