JOURNAL OF CRITICAL REVIEWS ISSN- 2394-5125 VOL 7, ISSUE 14, 2020 INSTRUMENT LANDING SYSTEM AND ITS REQUIREMENT IN INDIA Shivendra Shrivastava1, Rahul Kumar Verma2, Gp Capt M Shrivastava3 1,2Amity University, Noida 3Air Force [email protected], [email protected], [email protected] Abstract: The ILS is a navigational aid invented in the forties it helps aircrafts in landing. The pilots still consider the ILS as one of the most reliable means of guidance it continues to be used around the world. This paper examines what is an ILS its categories, components and the relevance of ILS in India. Since all Indian airports do not have ILS it causes disruption of flights, passenger discomfort and loss of business. The ILS has been compared with other advance systems of navigation in the market. Considering seamless movement of flights a necessity for business and development of India, the paper proposes ILS/GAGAN installation at all Indian airports. Key words - ILS, Localizer, Glide slope, Yagi antenna. BACKGROUND The development of an instrument landing system (ILS) began during World War I in the twenties but it was not until the thirties that some substantial research was carried out. The airports used to fire flares to guide the commercial airliners. There was a lot of research work carried out by USA and UK from 1930 to 1947 in developing a system in order to land aircrafts safely in low visibility conditions. This was a direct outcome of World War 2 since during the war the USAF bombers could not carry out bombing over Europe in foggy weather conditions. They found that the aircrafts could take off when visibility was low but on returning back from missions they could not land back on the runways due to poor visibility created by fog. Also during the war there used to be 'Black outs' where in the lights in the cities and airports were kept off to save them from enemy aircrafts bombing raids. The military aircrafts could not land at night in total darkness they wanted a system which would guide them on the correct path to the runway. These studies were done by the US Air Force in USA and by Royal Aircraft Establishment(RAE) in UK simultaneously they were also being done in France. The use of directional antennas using VHF & UHF band were being explored. There were various papers and patents published during that time in all these countries. The ILS came up as a result of the military research and development by these establishments. The first known trial of ILS took place in USA it was named Signal Corps System 51. The SCS51 can be called as the prototype of the current Instrument Landing System (ILS). [1] INSTRUMENT LANDING SYSTEM (ILS) This is a landing aid used by aircrafts it provides precision azimuth and descent guidance signals to the aircrafts in air coming in for arriving on a runway under typical or antagonistic climate conditions. At the point when all segments of the ILS framework the ground based and aircraft based are available the pilot can approach and land. The use of ILS by commercial airliners was started after it was accepted by the International Civil Aviation Organisation (ICAO) in 1945 as standard landing system. [2] Figure 1. Basic figure of ILS INSTRUMENT LANDING SYSTEM (ILS) IN INDIA The pilot of an aircraft has to establish visual contact with the runway in order to land at any airport, they need a minimum visibility of 5 Kms in VFR (Visual Flight Rules). In the winter season our country experiences fog in northern parts of the country over states like Punjab, Rajasthan, Delhi, UP , Uttrakhand, Bihar and West Bengal. Fog is caused by 1337 JOURNAL OF CRITICAL REVIEWS ISSN- 2394-5125 VOL 7, ISSUE 14, 2020 differential cooling between the rivers, lakes, water bodies and the land. The winds carry warm humid air towards the cool land surface causing in a dense fog(Fig-2). The dense fog over the airfield reduces the visibility to as low as 50 -100 meters as a result the pilots cannot see the airport runway due to poor visibility conditions. The pilots try to spot the runway and make attempts to land if they are unable to see the runway they go around again in consultation with the ATC control tower. If the attempts to land do not materialize and the visibility remains poor, planes divert go to other airports. The fog renders the airport unusable due to poor visibility. Figure 2. Fog in winter season Fog sends airports into a spin as aircrafts divert to other places. This disrupts flight schedules and causes delays for hours with passengers waiting for the fog to lift. The passengers get delayed and put to discomfort. Many times the airports have to be shut down due to low visibility. Every year numerous flights are delayed. The passengers miss their flights. They have to wait in the aircrafts or at the airports. This type of interruption costs airlines massive losses as their planes are not able to fly. An instrument landing system (ILS) works on the radio waves principle. The aircraft intercept the radio waves and use them as a guide to reach the runway. It provides lateral and vertical guidance to the pilot it uses a combination of radio signals to facilitate a safe landing. ILS has two components one is ground-based and the other aircraft based instruments. An instrument approach procedure is done during bad weather. An ILS approach chart provides pilots with information needed to fly an ILS approach for each airfield. The chart has the radio frequencies of the ILS, navigational aids and other requirements of the airfield. CATEGORIES OF INSTRUMENT LANDING SYSTEM The ILS system has been categorized into three types based on the accuracy of the equipment available on the ground at the airport. Similarly depending on precision of the compatible equipment on board the aircraft gives it the ability to use the corresponding facility on ground. The ICAO standardization of the categories is internationally accepted. The categorization is based on the decision height and the runway visibility (also called RVR runway visual range). Decision Height This height is very important for a pilot. In poor visibility when a pilot approaches the runway he has to carry out ILS landing. It is the height at which the pilot should decide whether to continue the approach or initiate missed approach if he does not spot the runway visually. The unit of measurement is meter/feet. The ILS categories are given below:- [2] (i) CAT I OPERATION. In this category directional information is provided up till the aircraft reaches an altitude of 60 meters or 200 ft. The Runway Visual Range should not be less than 550m (ii) CAT II OPERATION. In this category directional information is provided up till the aircraft reaches an altitude of 30 meters or 100ft. The Runway Visual Range should not be less than 350m. (iii) CAT III OPERATION. This category of ILS provides the guidance information up to the surface of the runway. The CAT III ILS operation are further subdivided into:- (a) CAT IIIA OPERATION. A ILS landing with :- a) the decision height lower than 30m (100ft),or no decision height. b) The runway visual range not less than 200m. 1338 JOURNAL OF CRITICAL REVIEWS ISSN- 2394-5125 VOL 7, ISSUE 14, 2020 (b) CAT IIIB OPERATION: A instrument approach and landing with :- a) the decision height lower than 15m (50ft), or no decision height b) the runway visual range less than 200 m not less than 50m. (c) CAT III C OPERATION: This approach is right up to the runway with no limitations. The categories can be represented with respect to Decision height in tabular form(Table-1) as follows:- Category Decision height RVR I 200ft /60mtr 550 mtr/ 1800 ft 350mtr/1200ft II 100-200ft /30-60mtr III A 100ft /30mtr 200mtr/700ft 50-200m /150-700ft III B 50ft /15mtr III C no limit None Table-1 Figure 3. The Airports that facilitate ILS in India 1339 JOURNAL OF CRITICAL REVIEWS ISSN- 2394-5125 VOL 7, ISSUE 14, 2020 CAT I & II airports CAT III Amritsar,Chandigarh,Delhi, Jaipur,Lucknow,Kolkata Airports Authority of India looks after the airports in India. It has installed CAT I and CAT II ILS system at 52 airports in the country they have been shown on the map(Fig-3). The CAT III B ILS system which is the latest and the most precise system has been installed at only six airports in India.(Fig-3) The small aircrafts and the older generation aircrafts are normally equipped with CAT I ILS or CAT II ILS systems because of space and weight constraints. Smaller aircrafts have lesser space on board carry less weight. The CAT III ILS is mounted on large aircrafts connected to the radio altimeter which gives the exact height of the aircraft to the pilot to determine decision height. WORKING OF INSTRUMENT LANDING SYSTEM In the system basically there are two important functioning blocks the transmitter element which is ground based and the receiver element which is aircraft based. GROUND BASED EQUIPMENT : TRANSMITTERS The ILS has ground based equipment consisting of Localizer and Glide slope, it is placed on the runway near the touchdown point. The antennas give vertical and horizontal guidance information when landing in poor visibility as shown in the Fig- 1. during a precision approach. The localizer is placed just before the starting of the runway and the Glide slope is offset to the side by 10m to 25 m.