RIZAL TECHNOLOGICAL UNIVERSITYCOLLEGE OF ENGINEERING AND INDUSTRIAL TECHNOLOGYDEPARTMENT OF ELECTRONICS ENGINEERING AND TECHNOLOGY

REPORT: INSTRUMENT LANDING SYSTEM (ILS)&MARKER BEACON

SUBMITTED BY: BESA, REYNALDO JR. ORTEGAGALA, CHARA CATADMANIBARRA, MELNY REAMBONANZAPAVILLAR, JOHN PAUL FORTUYAP, RAMON CHRISTOPHER EBIO

SUBMITTED ON: AUGUST 01, 2015

_ENGR. JAY KERIZ LIME_INSTRUCTOR

INSTRUMENT LANDING SYSTEM (ILS)What Is ILS? ILS is stand for Instrument Landing System. It has been existence for over 60 years. But today, it is still the most accurate approach and landing aid that is used by the airliners. ILS is a radio aid to the final approach and is used only within a short distance from the airport.History of ILS Tests of the first ILS began in 1929 The first scheduled passenger airliner to land using ILS was in 1938. A Pennsylvania-Central Airlines Boeing 247-D from Washington to Pittsburgh. In 1949, ICAO adapted an ILS standard developed by the US Army as a standard system for all of its member countries. Until the mid-1950s, only visual landing procedures were possible 1958-First IFR landing system developed 1966-First ILS system developed and tested at AIRPORT in USA 1968-First ILS applications installed at major airports 1974-ILS systems mandated by FAA for at least two major runways at all Regional, and International Airports.The Uses of ILS To guide the pilot during the approach and landing. It is very helpful when visibility is limited and the pilot cannot see the airport and runway. To provide an aircraft with a precision final approach (a precision approach is an approved descent procedure using a navigation facility aligned with a runway where glide slope information is given). To help the aircraft to a runway touchdown point. To provide an aircraft guidance to the runway both in the horizontal and vertical planes. To increase safety and situational awareness.*Note: When all components of the ILS system are available, including the approved approach procedure, the pilot may execute a precision approach.Poor Visibility Landings Scheduled service would be impossible without a way to land in poor weather.Types of Runway Approach1.Non-Instrument Runway (NI) A runway intended for the operation of aircraft using visual approach procedure2. Instrument Runway A runway intended for the operation of aircraft using instrument approach procedures Non-Precision Runway (NP) An instrument runway served by visual aids and a non-visual aid providing at least lateral guidance adequate for a straight-in approach Precision Runway (P) Allow operations with a decision height and visibility corresponding to Category 1, or II, or III Category of Precision Runway: Runway Threshold: Beginning of runway for landing. Touchdown zone: The first point for the aircraft should touch the runway during landing. Aiming point: serves as a visual aiming point for a landing aircraft.ILS Components ILS consists of Ground Installations and Airborne Equipments There are 3 equipments for Ground Installations, which are: 1. Ground Localizer (LLZ) Antenna To provide horizontal navigation2. Ground Glide path (GP) Antenna To provide vertical navigation3. Marker Beacons To enable the pilot cross check the aircrafts height.

There are 2 equipments for Airborne Equipments, which are: 1. LLZ and GP antennas located on the aircraft nose.2. ILS indicator inside the cockpitNote: The distance measuring equipment (DME) system gives the pilots distance to a DME ground station. The pilot can tune one DME station with the navigation control panel. The DME-distance shows on the navigation displays unit.ILS IndicatorGlidepath - Deviation from optimal glide pathLocalizer - Deviation from runway centre lineSignal Integrity Flag - Indicates if instrument is unreliableDots - Each dot on the instrument represents 2 of deviationSystem Architecture and InterfacesTechnology Infrastructure

Figure 1 Instrument Landing System

How ILS works? Ground localizer antenna transmit VHF signal in direction opposite of runway to horizontally guide aircraft to the runway centre line. Ground Glide Path antenna transmit UHF signal in vertical direction to vertically guide aircraft to the touchdown point. Localizer and Glide Path antenna located at aircraft nose receives both signals and sends it to ILS indicator in the cockpit. These signals activate the vertical and horizontal needles inside the ILS indicator to tell the pilot either go left/right or go up/down. By keeping both needles centered, the pilot can guide his aircraft down to end of landing runway aligned with the runway center line and aiming the touchdown. System OperationLocalizer One of the main components of the ILS system is the localizer which handles the guidance in the horizontal plane. The localizer is an antenna system comprised of a VHF transmitter which uses the same frequency range as a VOR transmitter (108,10 111,95 MHz), however the frequencies of the localizer are only placed on odd decimals, with achannel separation of 50 kHz. The transmitter, or antenna, is in the axis of the runway on its other end, opposite to the direction of approach. A backcourse localizer is also used on some ILS systems. The backcourse is intended for landing purposes and its secured with a75 MHz marker beacon or a NDB (Non Directional Beacon) located 35 nm (nautical miles), or 5,5569,26 km before the beginning of the runway.

Figure 2 Antennas of the Localizer System

The transmitted signal:The localizer, or VHF course marker, emits two directionalradiation patterns. One comprises of a bearing amplitude-modulated wave with a harmonic signal frequency of 150 Hz and the other one with the same bearing amplitude-modulated wave with a harmonic signal frequency of 90 Hz. These two directional radiation patterns do intersect and thus create a course plane, or a horizontal axis of approach, which basically represents an elongation of the runways axis see in the figure below.

Figure 3 Radiation pattern of the Localizers VHF AntennaUHF Descent Beacon Glide SlopeThe transmitted signal:The glide slope, or angle of the descent plane provides the vertical guidance for the pilot during an approach. Its created by aground UHF transmitter containing anantenna system operating in the range of 329,30335.00 MHz, with achannel separation of 50 kHz. The UHF glide slope is paired with the corresponding frequency of the VHF localizer.

Figure 4 The UHF descent beaconLike the signal of the localizer, so does the signal of the glide slope consist of two intersected radiation patterns, modulated at 90 and 150 Hz. However unlike the localizer, these signals are arranged on top of each other and emitted along the path of approach, as you can see in figure below. The thickness of the overlapping field is 0,7 over as well as under the optimal glide slope.

Figure 5 Radiation Pattern of the UKV Descent Beacon forming the Glide SlopeMarker BeaconsFor the purpose of discontinuous addition of navigation data with the value of a momentary distance from the aircraft to the runways threshold, the following marker beacons are used: Outer Marker (OM)The outer marker is located 3,56 NM (5.55611.112 km) from the runways threshold. Its beam intersects the glide slopes ray at an altitude of approximately 1400 ft (426.72 m) above the runway. It also roughly marks the point at which an aircraft enters the glide slope under normal circumstances, and represents the beginning of the final part of the landing approach.The signal is modulated at a frequency of 400 Hz, made up by a Morse code a group of two dots per second. On the aircraft, the signal is received by a 75 MHz marker receiver. The pilot hears a tone from the loudspeaker or headphones and a blue indicative bulb lights up. Anywhere an outer marker cannot be placed due to the terrain, a DME unit can be used as a part of the ILS to secure the right fixation on the localizer.In some ILS installations the outer marker is substituted by a Non Directional Beacon (NDB).

The outer position marker (blue) Middle Marker (MM)The middle marker is used to mark the point of transition from an approach by instruments to a visual one. Its located about 0,50,8 NM (9261482 m) from the runways threshold. When flying over it, the aircraft is at an altitude of 200250 ft (60,9676,2) above it. The audio signal is made up of two dashes or six dots per second. The frequency of the identification tone is 1300 Hz. Passing over the middle marker is visually indicated by a bulb of an amber (yellow) colour . It was removed in some countries, e.g. in Canada.

The middle marker (yellow) Inner Marker (IM)The inner marker emits an AM wave with a modulated frequency of 3000 Hz. The identification signal has a pattern of series of dots, in frequency of six dots per second. The beacon is located 60m in front of the runways threshold. The inner marker has to be used for systems of the II. and III. category.

The outer marker (white)Approach Lighting Systems (ALS)Normal approach and letdown on the ILS is divided into two distinct stages: the instrument approach stage using only radio guidance, and the visual stage, when visual contact with the ground runway environment is necessary for accuracy and safety. The most critical period of an instrument approach, particularly during low ceiling/visibility conditions, is the point at which the pilot must decide whether to land or execute a missed approach. As the runway threshold is approached, the visual glide path will separate into individual lights. At this point, the approach should be continued by reference to the runway touchdown zone markers. The ALS provides lights that will penetrate the atmosphere far enough from touchdown to give directional, distance, and glide path information for safe visual transition.

Figure 6 Approach Lighting SystemsOnboard EquipmentLocalizer ReceiverThe signal is received on board of an aircraft by an onboard localizer receiver. The signal of the localizer launches the vertical indicator called the track bar (TB, Fig.8). Provided that the final approach does occur from south to north, an aircraft flying westward from the runways axis (Fig.7) is situated in an area modulated at 90 Hz, therefore the track bar is deflected to the right side. Figure 7 Figure 8On the contrary, if the planes positioned east from the runways axis, the 150 Hz modulated signal causes the track bar to lean out to the right side. In the area of intersection, both signals affect the track bar, which causes to acertain extent adeflection in the direction of the stronger signal. Thus if an aircraft flies roughly in the axis of approach leaned out partially to the right, the track bar is going to deflect abit to the left. This indicates anecessary correction to the left. In the point where both signals 90 Hz and 150 Hz have the same intensity, the track bar is in the middle. Meaning that the plane is located exactly in the approach axis (Fig. 10).

Figure 9 Aplane flying nearly in the approach axis slighlty leaned out to the rightWhen the track bar is used in conjunction with aVOR, a lean out of 10 to one or the other side from the signalcauses afull deflection of the indicator. If the same pointer is used as an indicator of the ILS localizer, afull deflection will be induced by a2,5 diversion from the center of the localizers beam. Therefore the sensitivity of the TB is roughly four times greater in the function as an indicator of the localizer as at the indication of information from the VOR.

Figure 10 A plane flying exactly in the axis of approachIn case that a red NAV bat appears in the upper right section of the onboard ILS indicator (Fig.11), it represents that the signal is far too weak or out of the receivers reach and for that reason the pointers deflection cannot be considered to be accurate. The vertical pointer will return to the neutral position, meaning to the center of the indicator. A momentary display of the NAV bat, short deviations of the TB, or both instances happening at once can occur in the case that an aircraft flies between the receivers antenna and the transmitter, or some other obstacle gets into their way.

Figure 11 A plane situated out of reach of the VKV course beacons signalGlide slope receiverThe glide slopes signal is on board of a plane received by means of a UHF antenna. In modern avionics are the controls for this receiver combined with the VORs controls, so the correct frequency of the glide slope beacon is tuned in automatically at the instant when the localizers frequency is selected.The glide slopes signal puts the horizontal pointer of the glide slope into operation which intersects the TB, see Fig. 8 and Fig. 9. This indicator has its own GS bat which lights up whenever the glide slope beacons signal is too weak or the onboard receiver, hence the whole aircraft is out of the signals reach (Fig. 6).

Figure 12 Anexample of the displayed GS pointer notifying adiversion from the glide slope, atoo weak received signal, or an obstacle on the way.

The onboard indicator of the ILS system can be used by apilot to determine the exact position because it provides vertical as well as horizontal guiding. The case in Fig. 13 portrays both indicators in the middle, which means that the aircraft is located in the point of intersection of the course plane (horizontal) and the glide slope. The event pictured in Fig. 14 indicates that the pilot must descent and correct the flight course to the left in order to aquire the correct course and glide slope level. The case in Fig. 14 shows anecessity to ascend and adjust the flight course to the right.The apparent sensitivity of the instrument increases as the aircraft closes in to the runway. The pilot has to watch the indicator with attention so that he can keep an overlap of both needles of the pointer in the middle of the indicator. Thereby hell achieve a precise homing all the way to the touch down.

Figure 13 Both pointers in the middleFigure 14 A case when the aircraft is located right of the runways axis and too high over the glide slope.

Figure 15 A case when the aircraft is located left of the runways axis and too low under the glide slope.

Categories of ILSApproach categoryDecision height or alert height(minimum height above runway threshold or touchdown zone)Runway visual range("RVR")Visibility minimum

I200 feet (61m)550m or 2400ft (1200ft is approved at some airports), increased to 800m for single crew operations800m(1600ftor 1200ft in Canada)

II100 feet (30m)300m or 1000ftN/A

IIIA50ft < DH < 100 feet (30m)200 meters (660ft)N/A

IIIB0 < DH < 50 feet (15m)75 meters (246ft) < RVR < 200 meters (660ft)N/A

IIICNo DHNo RVRN/A

Note: *A Category III C system is capable of using an aircraft's autopilot to land the aircraft and can also provide guidance along the runway.*Special authorization and equipment required for Category II and III.Inoperative ILS Components1. Inoperative Localizer: When the localizer fails, an ILS approach is not authorized.2. Inoperative Glideslope: When the glideslope fails, the ILS reverts to a nonprecision localizer approach.Advantages Able to guide the pilot during approach and landing when visibility is reduced due to fog, rain, or snow. Able to guide the aircraft both in horizontal and vertical runway planes. Able to land an aircraft in a precision approach or touch-down. In newer aircraft, able to do Auto-land.Disadvantages Interference in the localizer and glideslope beam due to large reflecting objects, other vehicles or moving objects can reduce the strength of the directional signals.Limitations1. Installation of ILS can be costly due to the complexity of the antenna system and siting criteria.2. Localizer and glideslope beams are subject to hazardous reflections that would affect the radiated signal. So ILS critical areas and ILS sensitive areas are established. Positioning of these critical areas can prevent aircraft from using certain taxiways. This can cause additional delays in take offs due to increased hold times and increased spacing between aircraft.3. Localizer systems are sensitive to obstruction in the signal broadcast area like large building.4. If terrain is sloping or uneven, reflections can create an uneven glide path causing unwanted needle deflections.ILS Critical and Sensitive AreaThe ILS critical area is an area of defined dimensions about the localizer and glide path antennae, where vehicles, including aircraft, are excluded during all ILS operations. The area is protected to prevent aircraft or vehicles causing unacceptable disturbances to the signal-in-space.The ILS sensitive area extends beyond the critical area, where the parking and or movement of vehicles including aircraft is controlled to prevent the possibility of unacceptable interference to the ILS signal during ILS operations. The dimensions of the sensitive area depend of the intruding aircraft on the ground.

Points to Observe when Flying the ILS1. Carefully study the appropriate ILS approach chart before committing the aircraft to an ILS holding pattern or approach. 2. Ensure that equipment indications are normal and that the flag alarms are not visible before committing the aircraft to holding or final approach. 3. Identify the ILS aurally and select the marker beacon aural switch for aural identification before commencing final approach. 4. Check the aircraft altitude on reception of the marker beacons with the altitudes given on the ILS approach chart. This will provide a check that equipment is functioning normally. 5. Remember that a 5 dot indication either from the glide path or localiser course, at the outer marker, represents a greater physical displacement of the aircraft than at the middle marker. In other words, the sensitivity of the glide path and localiser increases as the aircraft approaches the runway threshold. 6. Major corrections to flight path should not be attempted after passing the outer marker. The approach should be discontinued if major corrections to the flight path are required at this stage. 7. Momentary fluctuations of the localiser needle may be caused by another aircraft taking off over the localiser aerials. Similarly, fluctuations of the glide path needle may be caused by a preceding landing aircraft. 8. If a visual reference has not been established at the authorised minimum, commence a missed approach without delay. 9. On a back beam approach or when outbound on a front beam, the localiser needle will still indicate the sector in which the aircraft is flying; but needle movement, in relation to aircraft heading corrections, will be reverse to the movement of the needle on a normal front beam approach. 10. On a back beam approach, the localiser aerials are situated at the landing end of the runway and, in the final stages of the approach, the localiser needle movements will be more sensitive than on the front beam approach. 11. If any doubt exists about the normality of any component of the ILS, check with the tower controller before commencing the final approach. 12. With modern localisers course reversals will be experienced outside a sector approximately 45 either side of the course centreline. Before commencing the approach check aircraft on centreline by reference to other aids. As with any other skill, perfection in flying the ILS is acquired with practice.