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How the Instrument Landing System Works?

An Instrument landing system (ILS) is equipment that utilizes an instrument-based navigation technique based on two radio beams that guide an aircraft landing on or approaching a runway. This combination of radio signals facilitate safe landings for pilots even during low-visibility conditions. As such, the ILS is an important part of keeping aircrew and passengers safe while on aircraft. With this in mind, this blog will cover how the ILS works, special features, and its importance.

The ILS provides aircraft with a recommended path to follow so that it maintains its horizontal position at the center of the runway while keeping an optimal vertical position necessary for smooth landing. As a result, the instrument landing system assembly consists of two subsystems.

The first is called the localizer (LOC) which provides lateral guidance, enabling the approaching aircraft to shift laterally into the recommended path. The second is called the glide slope (GS) or glide path, which prevents vertical deviation from the recommended path of descent. Guidance is provided to the ILS by way of a series of aerial signals from both a lateral and vertical direction. The LOC aerials transmit two intersecting beams on either side of the runway. The GS aerials are positioned on the aerodrome and transmit two intersecting beams; one below the vertical profile and one just above it. When an aircraft deviates from the recommended paths, a differential signal is produced, informing the pilot to adjust the aircraft’s position accordingly.

In some instances, the instrument landing system is aided by marker beacons and high intensity runway lights. If marker beacons are provided, they will likely be positioned on the ILS approach track at specified distances from landing. There are typically three markers, each at varying distances. The inner marker is located at the runway threshold, the middle marker is about 3500 feet from the threshold, and the outer marker is about 5 miles from the runway. Moreover, marker beacons are calibrated at 75 MHz, indicating both decision height points for approach and the distance to the threshold of the runway.

The ILS is not the only guidance system currently being used for aircraft operations. Another alternative is the microwave landing system (MLS), an all-weather precision radio guidance system that provides position and ground to air data. This information consists of an azimuth angle measurement, an elevation measurement, and a range measurement. In a MLS, lateral and vertical guidance is displayed on conventional course deviation indicators or presented on the multipurpose cockpit displays.

Beyond the need for landing systems, another important part of standard aircraft operations consists of landing gear support. Landing gear is typically attached to the wing spars or other structural surfaces on the aircraft. For example, retractable gear is firmly attached to the aircraft with enough grace so that it may be able to move into a recess or well when stowed. A trunnion arrangement is most common in this instance. The trunnion is a structural extension of the upper strut cylinder. It consists of bearing surfaces that allow the gear to move from the standard vertical position for landing and move to a stowed position necessary during flight. The trunnion alone cannot support the aircraft, and as such, a drag brace is used to limit how much the trunnion pivots. On some aircraft, the function of the drag brace is supplemented by the hydraulic cylinder which supports the aircraft during ground maneuvers.

As can be seen, landing systems are an integral part of standard aircraft safety operations. For this reason, it is critical to ensure that these systems are working properly. There are various components that work hand-in-hand with landing systems that, in some instances, need to be repaired or replaced. When you find yourself in need of such components, rely on NSN Gamut for all your operational needs. NSN Gamut is a leading distributor of NSN parts, aviation components, electrical connectors, and more. When you choose NSN Gamut as your sourcing solution, you get access to an unparalleled inventory of over 2 billion new, used, obsolete, and hard-to-find parts from global manufacturers we trust. Peruse our expansive catalogs, fill out and submit an RFQ form, and an account manager can draft a quote for your comparisons in 15 minutes or less. We are available to our customers 24/7x365.


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