Marker Systems PDF

Chapter 2 MARKER SYSTEMS Learning Outcomes  Ground Signals of Marker Beacon System  Airport Lighting Indicators  Airborne Marker Beacon System  Marker System Interface AVIONIC SYSTEMS MARKER SYSTEMS 2.1 Introduction The main purpose of the Marker Beacon system is to indicate...

Chapter 2 MARKER SYSTEMS Learning Outcomes  Ground Signals of Marker Beacon System  Airport Lighting Indicators  Airborne Marker Beacon System  Marker System Interface AVIONIC SYSTEMS MARKER SYSTEMS 2.1 Introduction The main purpose of the Marker Beacon system is to indicate to the pilot that the airplane is passing over a particular geographical position i.e.  Points along an air route  Points along an instrument landing path 2.2 Marker Beacon System Mostly markers are used on final approach to the runway (Figure 2-1), and are generally categorised into  Outer Marker (OM)  Middle Marker (MM)  Inner Marker (IM) The marker beacon stations transmit a 75 MHz RF signal modulated with either a 400, 1300 or 3000 Hz audio. This audio will be keyed (dots and/or dashes) to provide identification. The location of these markers from the runway threshold is shown in the Table 2-1. Table 2-1: DISTANCE MARKER FROM RUNWAY THRESHOLD OM 4 nm MM 3500 ft IM 250 ft ET0171/Chaganti Page 2-1 AVIONIC SYSTEMS OM RUNWAY MM IM TOP VIEW LOCALIZER TX GLIDESLOPE TX BLUE AMBER WHITE LIGHT LIGHT LIGHT SIDE 3000 ft VIEW GLIDESLOPE TX LOCALIZER TX 3500 ft 4 to 7 nm Figure 2-1 Marker Beacon Principle ET0171/Chaganti Page 2-2 AVIONIC SYSTEMS The inner marker beacon is rarely installed at civilian airports. When the aircraft is taking final course for landing, pilot can identify aircraft position on the landing path by Morse codes and lights on the cockpit instrumentation panel which are shown in the Table 2-2. By monitoring the lights and tones pilot can able to mark progress on final approach to the runway for safe landing. Ground marker beacon transmitters, when installed at airports, are usually monitored by monitor receiver. If transmitted power falls below 50% of normal, or if the modulation percentage falls below 70% or if the modulation keying fails, the airport controller will note the failure on a monitor indicator. Table 2-2: MARKER CODE LIGHT OM ─── BLUE MM ─ ─ ─ AMBER IM WHITE 2.2.1 Maker Operation  The pilot, on his approach to the airport will switch VHF Omni Range (VOR) frequency to a Localizer (LOC) frequency. The LOC frequency will also automatically select the corresponding Glideslope frequency.  The pilot, using conventional navigation techniques or radar guidance from air traffic control, will then begin to maneuver the aircraft onto the approach course.  The pilot could also be requested to enter a holding pattern using the outer marker beacon or a VOR intersection as one of the turning point in the holding pattern. ET0171/Chaganti Page 2-3 AVIONIC SYSTEMS  Once on the approach course with localizer and glideslope Figure 2-2, the aircraft will cross the marker beacons in sequence as the aircraft descends.  The aircraft, now within visual range of the run way and on direct course for it, is flown to a landing. 2.2.2 Airway marker Airway marker or Fan Marker transmits a high-pitched (3000 Hz) identification signal in the form of repeated dots and/or dashes. Fan markers are usually located within airways and their aerial systems are arranged to radiate narrow vertical fan-shaped beam (Figure 2-3) which extends across the width of the airway like a curtain drawn across a corridor. The thickness of the beam is limited, an aircraft flying through the fan marker receive its signals for a relatively brief period, thus ensuring that a position report can be given with accuracy. Fan markers are received in the aircraft on a separate marker receiver which provides two indications when the aircraft is over the reporting point:  A high-pitched coded signal delivered through the pilot’s headset or the cabin speaker.  A light flashes on the marker receiver indicator panel. Example 2-1: Singapore airport has outer marker placed at 4 nm from the run way, if an aircraft is at a height of 0.2 nm on the marker, Find its angle of approach? tan  Angle of approch  Aircraft height Mar ker dis tan ce ET0171/Chaganti Page 2-4 AVIONIC SYSTEMS RUNWAY CENTRE LINE Too High RUNWAY Slightly High On Glide Path Slightly Low ON GLIDESLOPE Too Low Figure 2-2 ILS Approach Ground Indicators ET0171/Chaganti Page 2-5 AVIONIC SYSTEMS FAN BEAM 10 nm AIRWAY Figure 2-3 Fan Marker ET0171/Chaganti Page 2-6 AVIONIC SYSTEMS 2.3 Airport Lighting Indictors Runway Visual Range (RVR) must be at least 1200 ft when the pilot begins his Category II approach. A Category II approach requires an airplane whose Category II equipment has been certified, in operation. In addition, special training programs must be certificated for the flight crew and for the maintenance people. A Category II approach can only be made at an airport which is Category II certified. The Localizer and Glideslope transmissions must meet stricter standards and must be monitored with failure indications available in the control tower. Figure 2-4 is an explanation of Category II airport equipment lighting. The Lights (LTS) are classified according to their functions i.e. Sequenced Flashing LTS Approach LTS Runway Edge LTS Touchdown Zone LTS Runway Centreline LTS  Sequenced Flashing Lights cause an apparent movement of the light toward the runway.  Approach Lights, which constitute a visible extension of the runway, these are designed so that the pilot can judge his position and altitude before touchdown.  Runway Edge Lights shows the available width of the runway for landing, and extends to full length of the runway  Touchdown Zone lights shows the touch down area for the aircraft, generally these lights are spread for about first 3000 ft of the runway  Runway Centreline Lights extends to full length of the runway ET0171/Chaganti Page 2-7 AVIONIC SYSTEMS LOCALIZER TX 1000 ft Runway Centre line LTS GLIDESLOPE TX Touchdown Zone LTS 400 ft 1000 ft Runway Edge LTS 1000 ft Approach LTS Sequenced Flashing LTS 2000 ft Figure 2-4 Airport Approach Lighting Indicators ET0171/Chaganti Page 2-8 AVIONIC SYSTEMS 1000 ft distance indication for the locations of the localizer and glideslope antennas are approximate, and vary from one installation to another Example 2-2: A 10 kW television transmitter is at a distance of 10 nm from the airport marker, what is the power density at the marker? Transmiter power Power density  4  dis tan ce 2 10 10 3   8W / nm 2 4 10 2 2.4 Airborne Marker Beacon System Aircraft marker beacon receiver system is shown in the Figure 2-5, with 75 MHz filter, RF amplifier and detector. From the detector comes whatever audio tone has modulated the carrier frequency. Three audio filters discriminate audio tones. The audio AC (about 6 volts) is used to light an indicator light. If the audio tone is 400 Hz, it lights a blue outer marker light, shown on the indicator panel. If it is a 1300 Hz tone, it lights an amber middle marker light. If it is a 3000 Hz tone, it lights a white marker/airways marker light. These tones, along with Morse code for identifying a station, are made available through an audio amplifier to the cockpit audio interphone system. These marker beacon system is turned on when the airplane electrical buses are energized, and the applicable MKR BCN circuit breaker is closed It receives VHF signals consisting of a 75 MHz carrier, amplitude modulated with 400,1300, or 300 Hz, depending on which of the three marker beacon signals is received. These signals are converted to an aural and visual output to indicate passage over a marker beacon transmitter. ET0171/Chaganti Page 2-9 AVIONIC SYSTEMS MARKER BEACON RECEIVER AUDIO OUTPUT 75 MHz AUDIO to FILTER AMPLIFIER INTERPHONE RF AMP and 3000 Hz DETECTOR FILTER AMP INNER 1300 Hz FILTER AMP MIDDLE 400 Hz FILTER AMP OUTER Figure 2-5 Airborne Marker Beacon System ET0171/Chaganti Page 2-10 AVIONIC SYSTEMS Airway markers are usually associated with specific aides to en-route navigation and provides with an exact position at the time of passing over the associated range station. Airway marker facilities are identified when the white lights come on and a 3000 Hz tone is heard. Outer and middle markers are associated with an instrument landing system. The outer marker is usually located directly below the point where an airplane on a localizer course should intersect the glideslope and start descending. An outer marker is identified when the blue lights come on and a 400 Hz tone is emitted. The middle marker is located near the runway usually under the point on the glidepath where a descent could be discontinued. A middle marker is identified when the amber lights come on and a 1300 Hz tone is emitted. 2.5 Marker System Interface Once the aircraft reaches near the airport, pilot selects Instrumentation Landing System (ILS) mode by changing the frequency on the control unit. This allows to pair LOC frequency with glideslope frequency. As aircraft takes approach course with localizer and glideslope, the Outer Marker (OM) beacon starts holding the aircraft on to the descent patch. Marker beacon antenna will receive beacon signals and the receiver can identify the beacon through the light indication on the instrumentation panel (Figure 2-6). Each beacon is also distinguished by Morse code received from the audio integration system. Outer Maker beacon generally will be an Automatic Direction Finding (ADF) station or VHF Omni Range (VOR) station located at 4 nm from the runway threshold. The Middle Marker (MM) is placed at 3500 ft from the runway threshold and is the decision maker to land or declare missed approach. Most of the airports are not installed with Inner Marker (IM) beacons. Once aircraft crosses all marker beacons and maintains localizer and glideslope deviation at the centre of the course deviation indicator, aircraft will approach with in the specified visual range from the runway threshold, which can land legally. Flight Warning Computer (FWC) monitors the conditions of the Marker system and issue a warning SIGNAL to the pilot in case of any failure. ET0171/Chaganti Page 2-11 AVIONIC SYSTEMS CAP F/O FLIGHT DISPLAY FLIGHT DISPLAY 1 2 2 2 2 2 10 10 10 10 IM IM 0 0 0 0 2 2 2 2 0 0 MM 0 0 NAVIGATION NAVIGATION MM DISPLAY 1 DISPLAY 2 1 0 1. 2 2 0 6.4 1 0 1. 2 2 0 6.4 OM OM DME-2 DME-1 DME-2 DME-1 V C N O O A R M V VOR/VOR CONTROL UNIT M VOR/VOR 1 1 0 1 8 8.. 0 0 0 0 MARKER BEACON FWC1 MARKER BEACON RECEIVER FWC2 RECEIVER AUDIO MARKER INTEGRATING MARKER ANTENNA SYSTEM ANTENNA Figure 2-6 Marker System Interface ET0171/Chaganti Page 2-12 AVIONIC SYSTEMS Notes ET0171/Chaganti Page 2-13