Mumbai University > Civil Engineering > Sem 6 > Transportation Engineering 2

Topic : Air Traffic Control

Difficulty : High

Instrumental Landing System (ILS):

• Now-a-days most of the major airports are equipped with the instrument landing system. This system is also termed as ‘Blind Landing System.’
• With the help of this system, the aircraft is brought to rest upon the ground by radio beam facilities which are installed on the airport.
• In short, the operator or pilot of the aircraft is directed by the radio beams installed on the airport so as to bring the aircraft on the ground i.e. on runways in a smooth manner.
• Thus instrument landing system gives lateral as well as vertical guidance to the aircraft during landing operation.

Significance of ILS:-

• When the weather conditions are bad or poor due to fog and when there is a poor visibility, then in such case with the help of ILS, the operator or pilot can able to make a safe landing of aircraft without viewing or seeing runway.
• ILS guides the pilot with safety on the optimum approach path for a safe landing
• If ILS facility is not installed at a particular airport, then the aircraft may be divided due to poor visibility to the adjoining airport having proper visibility. Hence it is more essential to have the facility of ILS on the airport so as to have the overall control over the aircraft for its safe landing.

Components of ILS:

1. Glide slope antenna
2. Localizer antenna
3. Outer and middle markers

These signals combine to form an invisible path along which the aircraft can approach and land.

1. Glide slope antenna :
   • This type of antenna emits a radio beam signal in the vertical plane at an angle of 2º to 3º from the horizontal
   • Glide slope antenna is a radio transmitter of very high frequency omni-directional range.
   • It indicates to the pilot the correct angle of descent to the runway or the ideal descent slope for the approach.
2. Localizer antenna :
   • It is a radio transmitter having a very high frequency of an omni-directional range (VOR)
   • Antenna transmits a radio beam signal in the vertical plane and this indicate the correct alignment to the pilot for approach to the runway. In other words, due to emission of such signal, a pilot can able to know whether he is to either left or right of the correct alignment for the approach to the runway.
   • It is situated along the extended center-line of runway end. Distance of location is about 300m form the far end of the runway.

3. Outer and middle markers :

   • This type of markers are small radio transmitters. It serve as position of reporting points.

     • Outer markers :-

       It is a small radio transmitter located at a distance of about 7000m or 7km ahead of the runway. Outer markers are also called as radio beacon which emits a purple light on the instrument panel in the cockpit of the aircraft.

     • Middle markers :-

       It is also a small radio transmitter located at a distance of about 1000m or 1km ahead of the runway threshold. It emits a amber light on the instrument panel in the cockpit of the aircraft.

   When pilot passes over these markers, the signals lights from the outer marker and middle marker falls on the instrument panel in the cockpit one after the other, he received a high pitched steady tone which indicate that he is on right approach.