Lecture 8: INSTRUMENT LANDING SYSTEM (ILS)

The first scheduled passenger airliner to land using ILS was in 1938. History of ILS ILS is stand for Instrument Landing System. Scheduled service would be impossible without a way to land in poor weather. The first scheduled passenger airliner to land using ILS was in 1938.

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. 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.

Poor Visibility Landings

The Uses of ILS To guide the pilot to perform landing. To provide an aircraft with a precision final approach. Provide both horizontal and vertical guidance. To guide the pilot to perform landing. It is very helpful when visibility is limited and the pilot cannot see the airport and runway. To help the aircraft to a runway touchdown point. To ensure flight safety. A Precision Approach is an approved descent procedure using a navigation facility aligned with a runway where glide slope information is given. When all components of the ILS system are available, including the approved approach procedure, the pilot may execute a precision approach.

Precision Runway (P) Aiming point Touchdown zone Designators Threshold Aiming point: Visual aiming point for a landing aircraft. Touchdown zone: landing airplanes first contact the runway. Threshold: Beginning of runway for landing. Basic Types approach and landing operations Visual Approach Aircraft is being operated in normal visual flight rules (VFR) Instrument Approach Aircraft is being operated in Instrument flight rules (IFR) IFR conditions to allow for a safe landing. Standard instrument approaches include International Civil Aviation Organization (ICAO), standard Navigation Aids (ILS, MLS, VOR, VOR/DME, NDB)

Precision Runway (P) Categories 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 components consists of Ground Installations and Aircraft Equipments Ground: Ground Localizer (LLZ) Antenna – To provide horizontal navigation Ground Glide path (GP) Antenna – To provide vertical navigation Aircraft Equipments LLZ and GP antennas located on the aircraft nose. ILS indicator inside the cockpit

ILS Components ILS Indicator inside the cockpit Ground Localizer Antenna Ground Glide Path Antenna

Ils indicator in the Cockpit

IANS / ATC Training / Courses / Basic / ACFT DME - ILS ILS Indicator Localizer indicator Deviation from runway centre line Glide path indicator Deviation from optimal glide path Edition 1.2 13 / 02 / 2006

IANS / ATC Training / Courses / Basic / ACFT DME - ILS Localizer Indication The vertical needle of the CDI indicates the localizer course. In practice, the same principle applies to tracking a localizer, as do to tracking a VOR, but greater care is required and greater accuracy is provided. The localizer consists of a single course and is four times more accurate and sensitive than a VOR. Thus, one dot left/right represents 0.5 o deviation from the course. Needle indicates direction of runway. Centered Needle = Correct Alignment Edition 1.2 13 / 02 / 2006

Localizer Indication The vertical needle is the localizer indicator. It provides the pilot with information required for horizontal. The localizer needle is tracked horizontally by adjusting the position aircraft in the direction of the needle (fly right or fly left).

Glide Path Indications IANS / ATC Training / Courses / Basic / ACFT ACFT 4 DME - ILS Glide Path Indications Needle indicates above/below glide path. Centered Needle = Correct Glide path Edition 1.2 13 / 02 / 2006

Glide Path Indications The horizontal needle is the glide path indicator. It provides the pilot with information required for vertical guidance. The glide path needle is tracked vertically by adjusting the rate of descent in the direction of the needle (fly up or fly down).

Ils GROUND INSTALLATIONS

Localizer Localizer is the horizontal antenna array located at the opposite end of the runway. Localizer operates in VHF band between 108 to 111.975 MHz. Normal reliable coverage of localizers is between 10 nm to 25nm.

Glide Path Glide Path is the vertical antenna located on one side of the runway about 300 m to the end of runway. Glide Path operates in UHF band between 329.15 and 335 MHz The GP signals coverage extends to a distance of 10nm. Glide Path operates in UHF band between 329.15 and 335 MHz

ILS principles

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 touch down.

VOR

Factors affected ILS signals Although the ILS system is very accurate and precise, it is very sensitive and its operation can be adversely affected by weather, FM broadcasts and vehicle/aircraft movement on the ground. Weather Snow and heavy rain attenuates the ILS signals thereby reducing the accuracy. FM broadcasts FM transmitters (radio stations) have wide bandwidths and it is possible for such stations transmitting on same frequencies that causing interference with the ILS signals.

Factors affected ILS signals Vehicle or aircraft movement on the ground. Every ILS installation has its critical area and its sensitive area. The critical area is protected during all ILS operations because the presence of vehicles or aircraft inside its boundaries will cause unacceptable disturbance to the ILS signals. Thus, these areas are important to prevent ILS signal disturbance. The sensitive area extends beyond the critical area and there the parking and movement of vehicles or aircraft is controlled ILS categories depends on 2 things, which are Decision Height (DH) & Runway Visual Range (RVR). The Decision Height (DH) is the altitude when the pilot must see the runway lights, else he must abort the landing. Runway Visual Range (RVR) means how far pilot can see on horizontal plane (how many feet pilot can see). The categories are: CAT I: DH>200 ft, RVR>2400 ft CAT II: 100 ft< DH <200 ft, RVR>1200 ft CAT III: in general DH<100 ft and RVR<700 ft The following must be fully serviceable to meet CAT II/III standards: Airport lighting: Approach lights Runway threshold lights Touchdown zone lights Centerline lights Runway edge lights Runway end lights All stop bars and lead-on lights Essential taxiway lights ILS components: Localizer Glide path

Marker Beacons

Marker Beacons Marking beacon is function as ILS markers. It consists Outer , Middle and Inner Markers. It functions to enable the pilot cross check the aircraft’s position. When the aircraft is passing over the marker beacons, they are indicated by light illumination and Morse Code tone through the cockpit speaker or headphones. A marker beacon is a particular type of VHF radio beacon used in aviation, usually in conjunction with an instrument landing system (ILS), to give pilots a means to determine position along an established route to a destination such as a runway. From the 1930s until the 1950s, markers were used extensively along airways to provide an indication of an aircraft's specific position along the route, but from the 1960s they have become increasingly limited to ILS approach installations. They are now very gradually being phased out of service, especially in more developed parts of the world, as GPS and other technologies have made marker beacons increasingly obsolete. There are three types of marker beacons that may be installed as part of their most common application, an Instrument Landing System:

Marker Beacons

Marker Beacons Lights in cockpit IANS / ATC Training / Courses / Basic / ACFT ACFT 4 DME - ILS Marker Beacons Lights in cockpit Marker beacon Cockpit light Identification Volume pitch Outer marker Blue 2 dashes / second Low Middle marker Amber Alternate dots and dashes 3 / second Medium Inner marker White 6 dots / second High Edition 1.2 13 / 02 / 2006

Marker Beacons Outer marker The outer marker should be located about 7km from the threshold. The cockpit indicator is a blue lamp that flashes accordingly with the received audio code. Middle marker Ideally at a distance of 1km from the threshold. The cockpit indicator is an amber lamp that flashes in accordingly with the received audio code. Inner marker Located at the beginning (threshold) of the runway . The cockpit indicator is a white lamp that flashes in accordingly with the received audio code.

Marker Beacons: the height aircraft Summary Marker Beacons: the height aircraft Localizer: horizontal guidance Glide Path: vertical guidance Primarily consists of three instruments: Marker beacons are used to measure how far aircraft until landing Glideslope or GlidePath for vertical guidance Localizer for lateral guidance All of these systems transmitt signals at different frequencies that are translated by electronics to determine the position of the aircraft

MICROWAVE LANDING SYSTEM

What is MLS? MLS (Microwave Landing System) is an advanced landing system. MLS operates in the Super High Frequency (SHF) between 5.031 to 5.090GHz. MLS was developed in 1978 to improve the uses of ILS system. It was chosen to replace ILS and installation date fixed to be 1995. However , advances in GPS system led to the expectations in many countries that the life of ILS could be extended until GPS would provide accurate landing guidance. Thus, only few countries installed MLS.

Why MLS need to replace ILS? ILS has a narrow and single approach path ILS has 40 channels and it signals are very sensitive, example if a vehicle passes near localizer, the ILS needle in the a/c may deflect. ILS signals are limited, as example: ILS is inflexible for helicopter landing as it has a single GP angle at any given installation.

Advantages of MLS MLS provide large coverage thus enable multiple approach paths to the same runway-horizontally & vertically. Large number of channels (200): can minimize the risk of signal interferences. Increase runway utilization even during poor visibility. Example: using ILS only 24 aircraft could land per hour, but with MLS, it allows an extra 6 aircraft an hour to land. Aircraft flying into Heathrow Airport in fog or poor visibility. On a clear day, about 44 planes an hour land at Heathrow. However, if the visibility drops and aircraft have to use the ILS system to land, only 24 aircraft could land per hour. This is because the radio transmitter at the end of the runway needs good line of sight to the approaching aircraft, but because it is at the far end of the runway, planes have to land and taxi clear before a full signal is restored. However, MLS allows an extra six aircraft an hour to land, meaning that while fog will still cause disruption, its effects will be less prominent.

MLS Ground Installations An MLS horizontal guidance station

MLS Ground Installations An MLS vertical guidance station