In this video, we will be looking at what is the Instrument Landing System and why is it useful for an aircraft.

What is an Instrument Landing System? An Instrument Landing System or ILS is a precision runway approach navigation system which provides guidance to aircraft during approach and landing. The ILS is a short-range guidance system which is used by aircraft to land safely on the runway, especially in bad weather or in low visibility conditions.

Let's look at how an ILS works.

How does an ILS work? An ILS provides horizontal and vertical guidance information to an aircraft for approaching a runway. The horizontal guidance information is used to guide an aircraft towards the center line of the runway. The vertical guidance information is used to allow an aircraft to descend smoothly towards the runway. Horizontal guidance is provided by a localizer and the vertical guidance is provided by a glide slope. In addition to the localizer and the glide slope, marker beacons and runway lights may be included as a need to the Instrument Landing System.

Let's look at the horizontal and vertical guidance information in more detail.

The Horizontal Guidance: The horizontal guidance or localizer guides an aircraft to track the center line of the runway. The localizer aerial is located at the end of the runway. It transmits two intersecting beams, one towards the left and the other towards the right of the runway. The beams intersect exactly over the center line of the runway. Depending on the location of the aircraft, there are different indications given in the cockpit. These indications are used to fly towards the right or towards the left to reach the center line of the runway.

The Vertical Guidance: The vertical guidance or glide slope is used to allow the aircraft to descend smoothly towards the runway. The glide slope antenna also transmits two intersecting beams, one beam above the required descent trajectory and the other beam below the required trajectory. Where the beams intersect represents the optimum path for descending towards the runway. So depending on the location of the aircraft, indications are provided in the cockpit to descend or to climb towards the required descent path and maintain this path.

Localizer and Glide Slope: By combining the signals from the localizer and the glide slope, the aircraft can descend safely towards the center line of the runway. These signals are undisturbed by the weather conditions or the time of day, which makes it very useful for an aircraft to descend and land safely in any condition. On modern aircraft having the autopilot system, the aircraft will automatically use the localizer and glide slope signals to approach a runway.

Additions to the ILS: The localizer and the glide slope are the primary requirements for an ILS. Marker beacons may be installed at specific distances along the approach path towards the runway. The outer marker beacon would be at five nautical miles from touchdown and the middle marker would be one nautical mile from touchdown. Nowadays, instead of marker beacons, Distance Measuring Equipment or DME may be installed to provide distance information. High intensity runway lights may also be used to improve the visibility of the runway in all operating conditions. Normally, even if the ILS signals are captured and followed, a certain amount of visibility of the runway should be available in order to continue with the approach and land on the runway. The runway lighting system improves the visibility of the runway.

The Instrument Landing System with localizer and glide slope signals is called a precision approach system. So that's all for my video on the ILS.