In aviation, a localizer (LOC) is a ground-based radio transmitter that provides lateral guidance to help pilots align their aircraft with the runway centerline during an approach and landing. It functions as a core component of the Instrument Landing System (ILS), which is critical for executing safe landings during night flights or low-visibility weather like heavy fog or rain. How It Works
Antenna Location: The antenna array sits at the departure end (the far opposite end) of the landing runway.
Dual Radio Signals: It transmits on a VHF radio frequency between 108.10 MHz and 111.95 MHz (exclusively using odd tenths, like 108.3 MHz).
Overlapping Lobes: The transmitter sends out two directional radio signals: one modulated at 90 Hz (projected to the left side of the runway) and one at 150 Hz (projected to the right side).
Cockpit Reading: The aircraft’s navigation receiver measures the difference in strength between these two signals. When both signals are perfectly equal, the cockpit’s Course Deviation Indicator (CDI) needle centers, meaning the aircraft is directly on the centerline. Signal Coverage and Sensitivity ILS: How The Instrument Landing System Works – Boldmethod
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