𝐈𝐧𝐬𝐭𝐫𝐮𝐦𝐞𝐧𝐭 𝐋𝐚𝐧𝐝𝐢𝐧𝐠 𝐒𝐲𝐬𝐭𝐞𝐦 𝐀𝐩𝐩𝐫𝐨𝐚𝐜𝐡

Instrument Landing System

🛩️An Instrument Landing System (ILS) enables pilots to conduct an instrument approach to landing if they are unable to establish visual contact with the runway.

🛩️It is defined by the International Telecommunication Union as a service provided by a station.

🛩️The ILS works using two components, a localizer and a glideslope.

🛩️The frequencies for the localizer are between 108.1-111.95 MHz and the glide slope between 329.15-335.0 MHz.

🛩️These frequencies are the carrier waves that the modulation takes place.

🛩️A pilot is only concerned with the localizer frequency as the navigation equipment knows the paired glideslope frequency for any given localizer frequency.

🛩️The localizer antenna broadcasts two lobes down the length of the runway for a few miles (typically 18 nm).

🛩️The glideslope antenna sits around the 1000 ft touchdown zone markers on the runway, offset a little bit from the runway.

🛩️It broadcasts a its own two lobes centered around a 3 degree slope.

🛩️The glideslope is generally usable about 10 nm from the runway, but is generally not used that far out.

🛩️The equipment in the plane responsible for using this signal comes in a few parts, an antenna, a radio and a navigation instrument.

🛩️The localizer signal is received the antenna used for the normal navigation signals (VOR) and there will be an additional antenna for the glideslope signal.

🛩️These signals will first go to a nav radio, which the pilot uses to select the localizer frequency (or a VOR frequency).

🛩️If a localizer frequency is selected, the radio will also listen on a specific glideslope frequency.

🛩️The data from the radio is then sent to whatever instrument you are displaying the data on.

🛩️The most primitive instrument is the VOR head with glideslope-type of needled navigation instrument.

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