Working of ILS and different categories and circuit patterns..

 ILS stands for instrument landing system is a ground based radio navigation system guide the pilot about vertical and lateral distance to watch the runway land the aircraft safely. As they are in instrument meteorological condition.

                         

Flying any aircraft for an ILS approach we have to know the standard approach chart( as I mentioned above chart it is of Mumbai airport runway-14) for particular runway.

2. ILS frequency and identifier Code.

3. glide slope angle and final approach point.

4. minimum descent altitude and ILS categories.

5. And go around pocedure/ missed approach procedure.

Let's talk more about the ground based equipment for better understanding of you guys seen this equipment at the end of the runway.

                       

This are nothing but a lcalizer antennas which transmits the radio waves to either side of the Runways. Like this 

90 hz frequency to the left hand side and 150 hz on the right hand side of the Runway this frequency range is upto 8 to 15 nm.

Ok now imagine the 90 hz frequency be in a yellow light and 150hz be in a blue light if our aircraft is flying in the blue zone of light then they should realize that we are right of the runway centerline we have to divert to the left hand side to allign to runway centerline which is blue in colour like this below diagram.

And also be displayed in the flight display unit by the diamond indicator. This localizer have frequency of 108 to 118 mz and it is same throughout the word to avoide the mismatch with other frequency and also have a specific _sos_.. codes. Localizer provides the lateral guidance to the aircraft.

2. Glide slope antenna- 

Provides the vertical guidance to the aircraft. glide slope angle to the runway in most cases is 3 degrees if we are above an below that then this will be considered as a false glide slope or steeper glide in most of the cases pilots carry out missed approach procedure or it can be manged by deployment of flaps and slats or by extraction of landing gear. This can be known to the pilot by flight display unit and diamond marker as I mentioned above. Like this below.

By showing too high or too low.

3. Marker beacons-

 This is for the how far  away we're from the runway center line or runway threshold.

This are further subdivided as

1. Outer marker

2. Middle marker 

3. Inner marker.

1. Outer marker- when we are flying under outer marker the blue light indicator activated. Like this

That means we are passing the outer marker same for the middle marker by yellow light and for inner marker by green lights.

4. DME- distance measuring equipment which gives the slant range towards the runway. by our aircraft position the standard instrument approach chart as mentioned above has to be fitted with DME as per ICAO. The standard localizer has to be fitted within ranges below for an DME upto.

The ILS has it's various different categories

In India we have upto cat-IIIB 

But the another countries like USA, Dubai have cat-IIIC even though they can land the aircraft in any situation bad wx, or by poor visibility the different categories will be discussed later.