What is the Aircraft Instrument Landing System (ILS)?

The aircraft instrument landing systems (ILS) are pilot aid systems that help with the approach and landing of an aircraft during the final stages of a flight operation. During standard weather conditions, the aircraft landing system helps a pilot execute a precision landing by providing both lateral and vertical guidance across a number of technologies. By working together with the destination air traffic controller, the aircraft can utilize a landing course with the ILS. In this blog, we will discuss the various instruments that make up the aircraft instrument landing system that pilots rely on.

The aircraft instrument landing systems include a variety of components including a localizer, glide path, marker beacons, distance measuring equipment, an approach lighting system, and runway visual range. The localizer is an antenna that is typically located at the end of a runway and allows for an aircraft to be guided on the right landing approach. Localizer antenna emit two broadcasts at both 90 Hz and 150 Hz in an overlap so that the ILS can pair with the localizer and glide slope frequencies to approach a correct glide path. For a pilot to be able to use the localizer, there must both be a receiver in the aircraft, as well as ILS facilities at the designated airport.

Aerial marker beacons are a very important part of the ILS system for approaching aircraft. Each signal is placed a certain distance from the runway and emits a VHF signal upwards for passing aircraft. As an aircraft passes over an aerial marker beacon, a small visual light begins to blink on their dashboard with the corresponding beacon letter. The first marker is the outer marker, located about four to seven nautical miles from the runway. When the aircraft detects this 400 Hz tone, they know that they are on their final approach. The middle marker is then found about half of a nautical mile away from the runway, emitting a signal at a frequency of 1,300 Hz. The last marker before the aircraft reaches the runway is the inner aerial marker, emitting a 3,000 Hz frequency at a location 200 to 1,500 feet away from the runway. Marker beacons have been heavily used since the 1930’s, but as GPS becomes more developed and available, markers have begun to be phased out due to being considered obsolete.

Another technology that may be used to supplement or replace marker beacons is distance measuring equipment (DME). DME is radio navigation technology that allows for a pilot to gauge their slant range from the ground station in nautical miles. With DME technology, equipment does not need to be set up outside of the runway such as markers do. If an airport utilizes distance measuring equipment in lieu of markers, approaching aircraft must have a working DME unit or an IFR GPS system.

As compared to much of the other ILS equipment, the approach lighting system helps the pilot line up their approach to the runway with visuals.The approach lighting system is composed of a chain of lightbars and strobe lights that line the runway approach to help pilots adjust their landing path as needed. Different airports and lighting systems may feature a variety of designs or complexity. The runway visual range (RVR) is another system that aids with a pilot’s visuals, determining the ability that a pilot has to see the runway surface markings. While this system used to be determined by humans, scatterometer devices are now placed on the runway which help determine visual range.

When flying, it is always important to have ILS systems that you can trust to bring you to touchdown safely and efficiently. At NSN Supplies, owned and operated by ASAP Semiconductor, we can help you find distance measuring equipment and aircraft instrument landing systems (ILS) parts you need, new or obsolete. As a premier supplier of parts for the aerospace, civil aviation, and defense industries, we're always available and ready to help you find all the parts and equipment you need, 24/7x365. ASAP Semiconductor is an FAA 0056B accredited and AS9120B, ISO 9001:2015 certified enterprise. For a quick and competitive quote, email us at sales@nsn-supplies.com or call us at +1-714-705-4780.


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