All about Instrument Landing Systems Antennas

2. Back course ILS approach

ILS or Instrument Landing System is a normal international civil aviation organization (ICAO) smooth landing aid. It helps to give accurate signals to aircraft while landing on the runway in any harsh or normal weather conditions.

ILS is an accurate means to navigate on the runway in harsh conditions. It gives the correct guidance on how to fly an aircraft with a precision approach. In this blog, we will talk about ILS Antenna, its components, features and validity of the antenna.

Components of ILS antenna

The different components in ILS Yagi Antenna are:

  • Glide path

This component in the antenna gives vertical guidance to the pilot during the approach. It is located at a height of 750 feet to 1250 feet down the runway from the threshold.

  • Localizer 

Localizer is the most important component in ILS antenna. It gives lateral guidance. Transmitter and antenna are placed on the centerline in the opposite end of the runway.

  • DME

Distance Measuring Equipment is generally connected with glide path and gives slant distance to the aircraft in relation to touch down point.

  • Markers

Markers are divided into outer marker and Middle marker. Outer marker is located 3 ½ to 6 NM from the threshold within 250 ft. of the extended runway centerline. It provides the pilot the flexibility to make a positive position on the localizer.

Middle Marker is located from 0.5 to 0.8 NM from the threshold on the extended runway centerline. This marker crosses the glide scope at a height of 200 to 250 ft. from the runway elevation.

  • Runway visual range or RVR

The pilot must be able to see the proper visual aids at the arrival at the decision height or the missed approach point.

  • Approach lighting system

Another important component of ILS antenna is approach lighting system. It helps the pilot to land the aircraft smoothly on the runway.

Steps to fly an ILS approach

ILS Omni Antenna located in the cockpit contains 2 needles. One needle indicates the glide slope and the second needle indicates the localizer. When the glide slop needle goes up, the pilot should pitch up as he is below the glide. On the other hand, the pilot must maneuver the aircraft to the left side. Localizer needle indicates that the aircraft is on the right side of the runway center line.

It is a bit difficult task to fly an ILS in windy atmosphere. Strong winds will remove the aircraft from the localizer. Pilots must be careful while fly an ILS antenna during the windy conditions.

Kinds of ILS approaches

The different types of ILS approaches are listed as under:

1. Localizer approach

As the name says, this approach uses the localizer component of the ILA antenna. In this approach, there is no vertical trajectory or the glide slope. Instead, the pilots must travel by cross-checking distance and altitudes. This approach is used when the glide slope for a runway is out of service.

2. Back course ILS approach

Back course ILS approach creates a localizer signal in the opposite runway. This signal is useful while flying a back course ILS. Unlike in normal ILS approach, the localizer indicator needle is reversed in a back course ILS. When the needle is on the left side, the pilot must move to the right side. On the contrary, the pilot must fly to the left side when the needle goes to the right side.

3. Offset localizer

In the case of offset localizer, the aircraft is guided on the localizer away from the runway. This localizer is useful for noise abatement as placing the localizer beam on the runway will keep incoming airplanes overhead the neighborhoods. LDA approaches are flown on the localizer up to a particular height. At the point, the pilot should identify the runway and make a turn and fly the aircraft.

4. ILS minima

The minimum for an ILS is known as the Decision Altitude (DA) for ILS CAT I approach. This altitude is a kind of barometric altitude provided by the aircraft’s altimeter. DA/DH is the point at which the pilot should have visual cues to land the aircraft. If there are no enough visuals at DA/DH, the missed approach must be tried by the pilot. DA for heavier aircraft is higher than lighter aircraft.

Final words

This is all about the instrument landing system antennas and their features, components, and approaches. ILS is further divided into several categories, such as CAT I, CAT II, CAT IIIA, and CAT IIIB.

Understanding the basics of ILS Directional Antenna is necessary for a pilot for smooth landing of aircraft on the runway. This blog explains everything related to an ILS Glide Slope Antenna and gives a better idea of how ILS antenna works in various kinds of weather conditions.

All about Instrument Landing Systems Antennas
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