GCRNA WITH MAFI PART-V Training Notes PDF

RESTRICTED TRAINING NOTES GCRNA WITH MAFI PART-V Apr 2019 RESTRICTED  RESTRICTED ii TRAINING NOTES GCRNA WITH MAFI PART - V No. 7 TETTRA SCHOOL AIR FORCE...

RESTRICTED TRAINING NOTES GCRNA WITH MAFI PART-V Apr 2019 RESTRICTED  RESTRICTED ii TRAINING NOTES GCRNA WITH MAFI PART - V No. 7 TETTRA SCHOOL AIR FORCE Compiled by: Sqn Ldr H Prasad SI GCRNA WO SS Barik WO IC GCRNA JWO NP Singh WO IC MAFI Apr 2019 Edition DESIGNED FOR TRAINING COURSE USE – DO NOT QUOTE AS AN AUTHORITY GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED iii AMENDMENT RECORD Date Amendments Page No. Authority Signature WARNING NOTE Précis has been prepared on date including amendment incorporated up to 03 Apr 2019. Current edition of the précis supersedes the previous précis issued up to 02 Apr 19. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED iv GCRNA WITH MAFI PART - V CONTENTS CHAPTER NAME OF SYLLABUS PAGE NO. EQUIPMENT INDEX NO. INSTRUMENT LANDING SYSTEM 22 57 1 - 62 (ILS) DOPPLER VHF OMNI RANGE 23 58 63 - 118 (DVOR) 24 RUNWAY VISUAL RANGE (RVR) 59 119 - 148 25 DATA RING 60 149 - 169 GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED v ACCOUNTING OF TRAINING NOTES SI Name Of Trainee Service Course Date of Sig of Date of Sign of No No No Issue Trainee return Trainee GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 1 CHAPTER- 22 INSTRUMENT LANDING SYSTEM (ILS) Introduction 1. Instrument Landing System (ILS) is the international standard system for approach and landing guidance. ILS was adopted by ICAO (International Civil Aviation Organization) in 1947. 2. Because of the worldwide-adopted ICAO's performance specifications, any ILS equipped aircraft can expect satisfactory operation from the system at any airport equipped with an ILS installation. 3. The ILS normally consists of VHF "Localizer" for runway alignment guidance, UHF "Glide Path" for elevation guidance and "Marker Beacons" for providing key checkpoints along the approach. At some airports, the Marker Beacons are replaced or supplemented by a "DME" (Distance Measuring Equipment) to provide continuous reading of distance. Fig 22.1: Typical Location of ILS Station Fig 22.1: NORMARC 7000B, ILS Cabinet GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 2 4. The Localizer (LOC/ LLZ), which provides lateral guidance, produces a course formed by the intersection of two antenna radiation patterns of equal amplitudes. One pattern is modulated by 90 Hz and the other by 150 Hz. The Course Line (CL) is an imaginary vertical plane on the extended centre line of runway where the 90 Hz and 150 Hz modulations are equal. 5. The signals received by the airborne receiver will produce a "fly right" indication for the pilot when the aircraft is on the left side of the course line in the 90 Hz predominance region. Similarly, a "fly left" indication will be produced for the pilot on the right side of the course line in the 150 Hz predominance region. 6. The Glide Path (GP) produces two amplitude modulated radiation patterns in the vertical plane, which intersect at the descent angle, namely the glide path angle. Below the glide path angle 150 Hz predominates giving a "fly up" indication. Above the glide path angle a "fly down" indication will be produced by the 90 Hz predominance. The GP is sited at a distance of about 300 m from the runway threshold and at a distance of about 120 m from the centre line of runway to give the 15 to 18 m threshold crossing height. The glide path angle is about 30. The glide path angle can vary from 2 0 to 40 depending on the aircraft type and size. 7. Instrument Landing System consists of Localizer, Glide Path & DME / Marker Beacons. ILS facilities are highly accurate and dependable means of navigating to the runway in IFR conditions. When using the ILS, the pilot determines aircraft position primarily by reference to instruments. 8. A complete Instrument Landing System (ILS) comprises: (a) A Localizer System (LLZ) NORMARC 7014B, producing a Radio course to furnish lateral guidance to the airport runway. (b) A Glide path System (GP) NORMARC 7034B, producing a Radio course to furnish vertical guidance down the correct descent angle to the runway. (c) Distance Measuring Equipment (DME_LP), located inside the GP station, replace the markers. Physical Description 9. The complete ILS electronic system is housed in a compact, wall mounted cabinet. The ILS cabinet has been configured for Cat II requirements. The cabinet consists of three sections. (a) The electronics card cage. (b) The change-over section. (c) The transmitter / PA section. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 3 10. The electronics card cage contains RF oscillators, LF signal generators, monitors, station control, RMS processor, and voltage regulators. 11. The change-over section contains coaxial relays to connect RF outputs from one transmitter to the antenna while the other is connected to dummy loads. 12. The transmitter / PA section contains PA blocks including couplers etc. for each output. All external connections are made to the rear part of the cabinet. The Remote Control Assembly (RCA 1750) is installed in the technical control room / RT cabin Fig 22.2: Typical Location of ILS Station ILS DEFINITIONS Decision Height 13. A height above the highest elevation in the touchdown zone, specified for a glide slope approach, at which a missed-approach procedure must be initiated if the required visual reference has not been established. Threshold – TRH 14. The start of the runway is marked with many longitudinal lines on the runway. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 4 ILS - Point A 15. An imaginary point on the glide path/localizer course measured along the runway center line extended, in the approach direction, 4 nautical miles (7.5km) from the runway. ILS - Point B 16. An imaginary point on the glide path/localizer course measured along the runway center line extended, in the approach direction, 3500 feet (1050 m) from the runway threshold.obl ILS - Point C 17. A point through which the downward extended straight portion of the nominal ILS glide path passes at a height of 30 m (100 ft) above the horizontal plane containing the threshold. ILS reference datum - Point T 18. A point at a specified height located above the intersection of the runway centre line and the threshold and through which the downward extended straight portion of the ILS glide path passes. DDM - Difference in Depth of Modulation 19. The percentage modulation depth of the larger signal minus the percentage modulation depth of the smaller signal, divided by 100. This is the parameter that indicates if the plane is to the right / left, above / below the correct approach. LLZ Course Line – CL 20. The locus of points nearest to the runway centre line in horizontal plane at which the DDM is zero. LLZ Course Sector – CS 21. A sector in a horizontal plane containing the course line and limited by the loci of points nearest to the course line at which the DDM is 0.155 LLZ Displacement Sensitivity (DS) 22. The ratio of measured DDM to the corresponding lateral displacement from the appropriate reference line. The nominal displacement sensitivity within the half course sector at the ILS reference datum shall be 0.00145 DDM/m (0.00044 DDM/ft). Hence; CS is 106.9 m (107.4 m) at threshold. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 5 Fig 23.3: LOC Course Sector Glide Path Course Line — CL 23. That locus of points in the vertical plane containing the runway centre line at which the DDM is zero. Glide Path Angle 24. The angle between a GP course line and the horizontal plane is known as glide path angle. Glide Path Sector 25. The sector in the vertical plane containing the course line and limited by the loci of points nearest to the course line at which the DDM is 0.175. Displacement Sensitivity (DS) 26. The nominal angular displacement sensitivity shall correspond to a DDM of 0.0875 at angular displacements above and below the glide path between 0.07q and 0.14q. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 6 Fig 22.4: Glide Path Sector SYSTEM REQUIREMENTS Operation Performance Categories 27 The ILS shall have system specifications, which satisfy the requirements laid down by national authorities. The most commonly used are those formulated by ICAO in the document "Annex-10 to the Convention on International Civil Aviation". 28. The ICAO requirements concern the facility performance category of the ILS. The operational performance category used depends on several factors, such as traffic density, weather conditions and obstructions. A higher category allows operations down to lower minimum as given in Table below: (a) CAT I - Provides reliable guidance information to an aircraft at a height of 60 m (200 ft) and above from the ground along the line of approach. (b) CAT II- Provides reliable guidance information to an aircraft at a height of 30 m (100 ft) and above from the ground along the line of approach. (c) CAT III - Provides reliable guidance along the surface of the runway. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 7 Non- precision Category I II IIIA IIIB IIIC approach guide Minimum 300 m 60 m 30 m Descending. 0 0 0 (1000') (200‟) (100') Altitude (MDA) 550/800 m 300/350 m Runway Visual 5 km 200 m 50 m (1800‟/2600‟) (985‟/1150‟) 0 Range (16000') (700') (150‟) (*) (**) (*) RVR of 550 m for aircraft category A, B, C and 800 m for category D (**)RVR of 300 m for aircraft category A, B, C and 350 m for category D TECHNICAL CHARACTERISTICS OF ILS 29. The technical specifications of Localizer are as follows: Localizer System NORMARC-7014B MODULE/SUB ASSEMBLY PARAMETERS TRANSMITTER Transmitter Dual Frequency range 108-112 MHz Frequency Tolerance ±4.0 PPM Output Power CSB Course 25 W Output Power SBO Course 1.6 W Output Power CSB Clear 25 W Output Power SBO Clear 1.6 W Output Power stability ±0.2 dB MODULATOR Modulator Dual Modulation depth 90 / 150 Hz 20% Identity Keyer Dual Modulation Depth 5-15% Adjustable Speed of Identification 7 Words/Min GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 8 Monitoring Dual PC Remote Maintenance and Windows Based RMM Software on PC Monitoring Software Number of serial ports Three serial ports RS 232: Local-One Remote-Two Security Three Level Password Access TRANSMITTER External Power Supply Unit 230V + 15%/ - 20%, 45-55 Hz Input Voltage External PSU Output Voltage 27.6 V External PSU Output Current 25 A Max LLZ Input Voltage 22-28V DC LLZ Current Consumption 20A Max LOCALIZER ANTENNA NORMARC 7212A Front Course Course Width 2.8⁰ TO 6.0⁰ Adjustable Coverage and Clearance Inside ± 35⁰ Off Course Line Back Course Front –to-Back Ratio 26 dB Minimum ANTENNA ELEMENT Type LOG PERIODIC DIPOLE ANTENNA Gain 9.5 dBi Horizontal Beam Width ± 23⁰ VSWR 1.2:1 Max Length/Width 2.8/1.3 Meters Weight 35 Kgs Number of LPDA Antennas 12 Width of Antenna Array 26 Meters (12 LPDA antennas) Operating Temp -40⁰ C TO +70⁰ C GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 9 Glide Path NORMARC 7034B 30. The technical specifications of Glide Path are as follows: MODULE/SUB ASSEMBLY PARAMETERS TRANSMITTER Transmitter Dual Frequency Range 328.6-335.4 MHz Frequency Tolerance ±4.0 PPM Output Power CSB Course 8W Output Power SBO Course 0.8 W Output Power CSB Clear 1W Output Power Stability ±0.2 dB MODULATOR Modulator Dual Modulation Depth 90 / 150 Hz: Course 40% Transmitters Modulation Depth: Clearance 80% (SDM) Transmitters 90 Hz Component 20% 150 Hz Component 60% Identity Keyer Dual Modulation Depth 5-15% Adjustable Speed of Identification 7 Words/Min Monitoring Dual PC for Remote Maintenance and Windows Based RMM Software on PC Monitoring Software Number of serial ports (RS-232) for Three Serial Ports RS 232; RMM Local-One Remote-Two GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 10 MODULE/SUB ASSEMBLY PARAMETERS Security Level for RMM Three Level Password Access External PSU Input Voltage 230 V + 15%/ - 20%, 45-55 Hz External PSU Output Voltage 27.6 V External PSU Output Current 25 A Max GP Input Voltage 22-28 V DC GP Current Consumption 16 A Max Glide Path Angle 2.0⁰ TO 4.0⁰ Adjustable Front to Back Ratio 17 dB Min ANTENNA ELEMENT Type Kathrein 713.316 Gain 12.5 dBi Beam Width ± 12.5⁰ VSWR 1.1:1 Max Length/Width 2.8/1.3 Meters Weight 35 Kgs Number of Antenna Elements 3 Height of Antenna Mast 15 Meters Operating temp -40⁰ C TO +70⁰ C PRINCIPLE OF OPERATION OF ILS Space Modulation 31. Space modulation is a radio amplitude modulation technique used in Instrument Landing System that incorporates the use of multiple antennas fed with various radio frequency powers and phases to create different depth of modulation within various volumes of the three dimensional air space. This modulation method differs from internal modulation methods inside most other radio transmitters in that the phases and powers of two individual signals mix within airspace, rather than in a modulator. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 11 An aircraft with an on-board ILS receiver within the capture area of an ILS, (Glide Path and Localizer range), will detect varying depths of modulation according to the aircraft‟s position within that airspace, providing accurate position information about the progress to the threshold. The guidance signal 32. The ILS guidance information is based upon comparison of the depth of modulation of the 90 Hz and 150 Hz modulation signals (called guidance tones). This difference in depth of modulation (DDM) is the main parameter by the airborne receiver. The variation of DDM in space is obtained by radiation of the amplitude modulated (AM) signals, both modulated with 90 Hz and 150 Hz. The signals are named CSB and SBO. The CSB (Carrier and Sideband) is a signal which is amplitude modulated to equal depths by the guidance tones. The SBO (Sideband Only) signal takes the form of a double sideband, suppressed carrier with the two guidance tones modulated in opposite phases. 33. The CSB and SBO signals are shown in Figures respectively, expressed in the time domain. Fig 22.5: The CSB waveform seen in the time domain. Upper diagram is 90 Hz, an lower is combined 90 + 150. Time scale in milliseconds GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 12 Fig 22.6: The SBO waveform seen in the time domain. Upper diagram is 90 Hz, middle is 150 Hz, lower is combined 90 - 150. Time scale in milliseconds DDM and SDM definitions 34. DDM is defined as DDM = m 150 – m90 for modulation level 2m 35. SDM is defined as SDM = 2m for modulation level 2m Fig 22.7: CSB and SBO GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 13 36. When SBO amplitudes are less than the CSB modulation depth, DDM is equal to the magnitude of the SBO amplitudes 90 plus 150 in reference to the carrier amplitude. 37. By convention 90 Hz and 150 Hz SBO amplitudes are equal, consequently DDM = 2.SBO / CSB Fig 22.8: CSB and SBO 38. DDM is proportional to the cosine of the phase angle between CSB and SBO. The complete formula for DDM including CSB/SBO phase relation is: DDM = (2.SBO/CSB) COS ϕ Any phase error ϕ will reduce the DDM magnitude. Fig 22.9 CSB and SBO GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 14 For ϕ = 90, cos ϕ = 0, consequently DDM =0. The result is maximum DDM, cancellation of the 90 Hz component. Fig 22.10: CSB and SBO Coverage of ILS 39 In the coverage volume given in Figure, the field strength shall not be less than 40 mV/m (-114 dBW/m). In addition there are additional signal requirement for the distance closer than 18.5 km (10NM). This varies depending on the category of the system. Fig 22.11: coverage of ILS GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 15 Course Alignment 40. The mean course line shall be adjusted and maintained within ± 10.5 meters (± 35ft) (Cat-I) or ± 7.5 meters (± 25ft) (Cat-II) recommended ± 4.5 meters (± 15ft) or ± 3 meters (± 10ft) (Cat III) from the runway center line at the ILS reference datum. ILS Site 41. A complete ILS site installation consists of: (a) ILS cabinet (LLZ/ GP) with dual TxRs (2 Course and 2 Clear TxRs) (b) Dual monitors (three monitors if Hot Stand By - Cat III) (c) Antenna Distribution Network/ Unit (Splits the signal from the transmitter into the number of antennas used) (d) Antennas (12 LPDA Ant for transmission and 1 NF Yagi Ant for monitoring) (e) Monitor Combination Network/ Unit (Combines the signals from the monitor loop inside the antennas to monitor signals) (f) External power supply unit with battery charger and batteries for dual power supplies (g) Remote Control master (RCA) in RT cabin (h) A slave panel (RMA) in ATC for status monitoring (j) Computer running the RMM software (k) A Far Field Monitor (FFM) may be used in a Cat III LOC THE NORMAC 7013B-LOCALIZER CABINET (FROM FRONT) Localizer Description 42. The Localizer system comprises a NORMARC 7014B Localizer Cabinet and a Localizer Antenna System NORMARC 7212A (12-element two-frequency). A remote control unit (RCU) is located in the RT Cabin and is connected to the Localizer station by OFC. 43. The antenna array of the ILS Localizer transmitter is located on the extension of the centre line of the instrument Runway of an Airfield, but is located far enough from the stop end of the Runway to prevent it being a collision hazard. The Localizer antenna radiates a field pattern directed along the centre line of the Runway towards the middle and outer markers. The antenna also furnishes information outside the front course area in the form of full fly-left or full fly-right indications (CLEARANCE). GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 16 44. All Localizer installations transmit a STATION IDENTIFICATION in Morse code at periodic intervals. This is a 1020 Hz tone that is keyed to form the basic station identifier. Some installations transmit Voice periodically in addition to the Morse code. 45. The Localizer is designed to provide a signal at a minimum distance of 25 miles within ± ±10 degrees, and at a minimum distance of 17 nautical miles between ± 10 and ± 35 degrees from the front course line. 46. The Localizer antenna system radiates two different signals, the carrier plus sideband (CSB) and the sideband only (SBO). The CSB signal is a carrier signal amplitude modulated with 90 Hz and 150 Hz, the depth of modulation for both tones is 20%. The SBO is an amplitude-modulated signal with a suppressed carrier where the 90 and 150 Hz tones are in phase opposition. 47. The CSB and SBO signals are generated in the Localizer transmitter and are fed, via the antenna distribution unit, to each antenna element with the correct phase and amplitude. 48. The DDM, which provides the azimuth information, can be expressed by the ratio of the received amplitude of the CSB and SBO signals: 49. The angle is the RF phase between the CSB and SBO signals. The various features of LLZ are: (a) Two-Frequency Localizer System with Hot-Standby Monitoring. (b) Dual transmitters/modulators. (c) Dual monitors for CL, DS, CLR and NF. (d) Monitor for internal monitoring of standby CL, DS and CLR (e) Antenna simulation network for standby monitor. (f) Local control panel with On/Off, Change-Over, Main Selection, Local/Remote and Manual/Auto switches. (g) Local keyboard and display for the Remote Monitoring System (RMS) with 7 dedicated push button keys for local operation of the RMS. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 17 MAINS SWITCH PSU MODULE RF OSCILLATOR MON FRONT END MON SYSTEM LF GENERATOR LCP (TCA) RMS PANEL COURSE TXR CLEAR TXR Fig 22.12: NORMARC 7000B, Localizer Cabinet Antenna Arrays 50. All ILS antenna systems comprise more than one radiating element. When two or more antenna elements, fed from the same transmitter, are located in a straight line they form a linear antenna array (normally referred to namely as an antenna array). The radiation pattern from the array is the product of the antenna pattern and the pattern from the antenna array with isotropic elements. 51. The array radiating elements are log-periodic dipoles (LPDA) which have the following advantages over the standard dipole/reflector antenna: (a) Reduced antenna height, thus reducing obstacle clearance problems. (b) Suppressed high angle radiation, reducing reflections from over-flying aircraft. (c) Robust construction (without guy-wires) giving reliable performance under adverse weather conditions. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 18 (d) No critical reflecting screen and reduced antenna coupling, resulting in easy adjustments Fig 22.13: Block Diagram of LLZ Signal Distribution 52. The Antenna Distribution UNIT (ADU) feeds the antenna elements with the proper amplitude and phase of the CSB and SBO signals. By changing the amplitude of the SBO feeding the ADU, the Course Sector Width is adjusted. 53. The Course Line is determined of mainly the mechanical alignment, but can be adjusted by using a phase shifter inserted at the output of the ADU to one of the antennas. Localizer Antenna System 54. The NORMARC 7212A is a twelve-element array for a two-frequency system. The two-frequency antenna systems are designed for use at Airfield sites which have large reflecting objects which could, with one-frequency systems, cause significant course GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 19 structure degradations. The use of LPDAs has made it possible to realize the desired radiation patterns from an array having very few elements. The antenna elements are mounted on a frangible aluminum framework at a height of 3 meters above the ground. 55. The two-frequency systems employ a separate clearance signal, which allows the course radiation pattern to be formed with very little radiation outside of the required signal coverage out to 35 deg. The antenna systems include distribution and monitor units and a near-field course-line monitor antenna is also provided. 56. Localizer antenna systems comprise 12, 16, 20 or 24 antennas depending on site topography and buildings near the runway. Type of antenna used in LLZ is Log Periodical Dipole Antenna. Two versions of 12 elements systems are available, one single frequency system and one dual frequency system (with clearance signal).The 16, 20 and 24 elements system includes a clearance signal. Fig 22.14: Localizer Antenna View Localizer Log Periodic Dipole Antenna (LPDA) 57. The LPDA is manufactured from salt-water resistant aluminum. To be able to withstand winter condition the whole electrical antenna is protected by fiberglass reinforced polyester cover plus dipole cover tubes of Polypropylene. 58. The length of antenna is 2.8 meters and the width is 1.3 meters. The weight is approximately 35 kg. The gain of the antenna is 9.5 dBi. 59. Inside the antenna there is a monitor loop picking up the amplitude and phase of the distributed signal of that antenna and routing that back to the MCU. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 20 60. The LPDA belongs to a class of antennas with broadband properties. These antennas will in theory have an infinite bandwidth if their dimensions were unlimited. Fig 22.15: LPDA Antenna 61. The term "log-periodic" refers to the logarithmical frequency periodic variation of antenna properties. The LOC antenna is a LPDA consisting of seven dipoles. The feeding of the LPDA is to the apex (the smaller end) and is such that each consecutive dipole element is fed 180° in respect to the next element. 62. The resultant field backwards from two elements will be cancelled due to the small distance compared to a wavelength. Due to the distance between elements the phase difference between these leads to an in-phase forward field from the element. The radiation then is off the apex of the antenna. ADU and MCU of Localizer 63. The ADU and MCU of the LOC are mounted inside a stainless steel cabinet hat is meant to be installed outside. Normally the networks are mounted on stay bars behind the middle pair of antennas. The reason for this is to reduce cable loss. Antenna Distribution Unit (ADU) 64. The purpose of the ADU is to split up the four signals from the transmitter and distribute them to the antennas. Each of the antenna pairs has individual phase and amplitude to produce the correct signal in space. In addition the ADU contains circuits to monitor the cables to and from the antennas and the antenna itself (DC-loop).On the right side there is one CL phaser for fine adjusting the electrical Centre line. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 21 Fig 22.16: Antenna Distribution Unit Monitor Combining Unit (MCU) 65. The signal samples from the antennas are fed to the MCU where they are combined to produce the three monitor signals: CL, DS and CLR. The network has two line phase shifters for fine adjustment of the CL and DS signals. Fig 22.17: MCU GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 22 Localizer Monitoring 66. The monitor philosophy is based upon: (a) High degree of ILS signals availability. (b) Monitor all essential parameters. (c) Monitored parameters correlate with the far-field. (d) Fail-safe monitor circuits. (e) Control of critical and Sensitive Areas 67. To ensure correct operation of the localizer, it is monitored in three different ways. A near field antenna, which is located about 50 to 200 m in front of the antenna system, monitors the course line. The main purpose of the NF antenna is to detect mechanical changes in the antenna array. The monitor system comprises integral monitoring and near-field monitoring. 68. The integral monitor detects any changes of the CL, CLR, DS, SDM and RF caused by the transmitter or antenna system. The near-field monitor (NF) detects changes due to any misalignment of the antenna element position or the conditions of the ground close to the antenna system. The course line DDM is measured. 69. One important aspect of the monitors is their correlation with the far-field signal. Since a field monitor located in front of the antenna system cannot be located in the far- field due to obstruction clearance requirements, this monitor signal will have a limited correlation with the far-field. 70. Hence, an alarm condition in the far-field will not always be detected by the near- field monitor. This problem is resolved by using the NORMARC integral monitors. 71. As the far-field signal is obtained in the monitor by taking samples of the signal from each antenna element and combining them in their far-field RF phase-relationship, a correct signal is monitored. Obstacles close to the ILS antenna systems could produce hazardous radiation not detected by the monitor systems. 72. To take care of any dangerous disturbance of the ILS signals, the size of the Critical Area is determined and kept under control by a fence or signs. 73. To determine the size, advanced computer modeling techniques are used. 74. Multipath effects from parked and taxiing aircraft will not be detected by the monitor system. Large aircraft (B747) could produce beam bends exceeding the specified limit at certain parts of the Airfield. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 23 75. To determine the Sensitive Area, the effect of worst-case orientation of B747 at several locations of the airport is computed. This area should be kept free from any aircraft during an ILS approach. GLIDE PATH DESCRIPTION Glide Path 76. The glide path system comprises a NORMARC 7034B Glide Path Cabinet and a Glide Path Antenna System (NORMARC 3545 M-array). A remote control unit (RCU) is located in the RT Cabin and is connected to the Glide Path station by OFC. To shape the glide path signal, ground plane reflection from an area in front of the antenna array is necessary. The glide path site may be located on either side of the Runway, but the most reliable operation will be obtained if the site is selected on terrain least obstructed by taxi-ways, aircraft holding aprons, parking ramps, buildings, power lines etc. The site should offer the widest area of smooth ground with possibilities of leveling without excessive physical or economical effort, if indeed leveling is deemed necessary. 77. The glide path antenna system should be located at a distance of 75 to 200 m from the Runway centerline. The distance from the Runway threshold is a function of several factors upon which establishment of the optimum operational conditions depend. These factors are: (a) The glide path angle. (b) Threshold crossing height requirements. (c) Obstruction clearance requirements. (d) The slope of the terrain in front of the antenna system. (e) The extent of smooth terrain in the site area and beyond the threshold. 78. The CSB and SBO signals generated in the GP cabinet unit are amplitude modulated by 90 and 150 Hz signals, the depth of modulation of the CSB signal being 40%. The CSB and SBO signals are fed to the antenna elements via the antenna distribution unit. The ground plane in front of the antenna system, the beam forming area, is utilized to reflect radiation from the elements so as to form the glide path field patterns. The radiated signals are monitored both integrally and by a near-field monitor. The various features of Glide Path are: (a) Two frequencies Glide Path System with hot standby monitoring Dual transmitters/modulators. (b) Monitor for internal monitoring of standby CL, DS and CLR GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 24 (c) Antenna simulation network for standby monitor. (d) Local control panel with On/Off, Change-Over, Main Selection, Local/Remote and Manual/Auto switches. (e) Local keyboard and display for the Remote Monitoring System (RMS) with 7 dedicated push button keys for local operation of the RMS. (f) Three RS 232 Interface for the RMM i.e. for Local, Remote 1and Remote 2. (g) (h) Separate wall mounted Dual Power Supply/battery Charger BC 1361. (i) Remote Control Unit RCA 1240 with ON/Off, changes over switches and LED status indicators. The RCU is configured with audible alarm. (j) No break power supply system (batteries 24 V/110 Ah and Cables included). Fig 22.18: NORMARC 7000B, Glide Path Cabinet and Glide Path Antenna GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 25 Fig 22.19: Glide path Block Diagram Glide Path Antenna System 79. The glide path antenna element is a stacked dipole antenna with reflector, housed in a fiberglass radome for weather protection. A signal coupler network linked to all dipole elements is used to monitor the signal fed to the antenna element. The signal from the coupler is about 35 dB below the level of the feed signal. 80. The M-array utilizes a three element antenna array to achieve a satisfactory signal performance with less strict requirements for the terrain in front of the glide path site, and the necessary reflecting area is less than for either the NR or SR. It is especially well suited for sites with a hill beneath the approach sector. 81. At elevation angles lower than about one degree, the signal strength is not great enough to satisfy the ICAO coverage requirements with a reasonable RF power. To overcome this problem, a transmitter generating a "fly-up" signal is used to create a strong signal below one degree angles. This clearance transmitter works on a slightly different carrier frequency than the main transmitter so as to utilize capture effect in the airborne receiver. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 26 82. The clearance signal is fed to the lower and upper antenna elements which results in a radiation pattern having a null at the glide path angle. 83. The clearance signal has a 150 Hz dominant modulation with a DDM of about 40%. Due to the capture effect, reflections of this signal have no significant effect on the glide path. ANTENNA MAST KATHREIN STACKED DIPOLE ANTENNA Fig 22.20: GP Antenna 84. There are several types of Glide Path antenna systems, and the choice of system is depending on site topography. The three image systems Null-reference, Sideband- reference and M- array require a reflection plane in front of the antenna system. The size of this area is different between the systems. GLIDE PATH MONITORING Integral Monitoring 85. The signals from the pickup probes, which are proportional to the radiated signals from the antenna elements, are fed through the equal length monitor cables to the Monitor Network. 86. The far field Glide Path Angle, the lower Sector Width and the Clearance (if applicable) are simulated in the network by combination of the signals. 87. In order to simulate a specific monitor point in the far field we monitor the signal from each antenna with correct level and phase and then combine the signals into one output signal. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 27 Near Field Monitoring 88. The GP near field monitor measures variations of the radiated signals, which may result from alterations in the condition of the ground near to the antenna system or mechanical misalignment of the antenna elements. 89. The distance to the monitor antenna is so short that there will be a large phase error caused by difference between the path lengths to the antenna elements. 90. This phase error will result in large variations of the DDM along the 3° path, depending on the distance for the radiating antenna elements. Antenna Distribution Units 91. The unit is housed in a cabinet for installation in the Glide Path cabin. The M- array system use identical units which comprise coaxial elements. The system can be optimized to a specific site by using the adjustable power dividers and line stretchers. Monitor Combining Units 92. The signals to be monitored are formed by adding the monitor probe signals from each antenna element in a proper amplitude and phase relationship, which are given by the radiation patterns of each element for the elevation angle to be monitored. The monitor units consist of a strip-line network, attenuators and phase shifters, housed in a cabinet designed for wall mounting inside the Glide Path shelter. SYSTEM BLOCK DIAGRAM Interconnection between the modules 93. The block diagram below shows the main signal flows between the major blocks in the ILS cabinet. The two monitors receive RF signals from the monitor network. In the monitors the signals are detected and checked to see if they are outside their tolerance. An alarm signal is then sent to the Tx Controller that takes the decision if the transmitters are to be turned off or not. The Tx Controller also controls the Change-Over Section. 94. The RMS is continuously checking all built in test points from all the other modules. If any of them exceeds its predefined limit a Maintenance Warning will occur. Transmitter 95. The transmitters are duplicated. On the Dual Frequency ILS the DF (difference frequency) between the Course and the Clearance transmitters are 10KHz for the LOC and 15kHz for the GP. The Course frequency is always the higher of the two. Each transmitter consists of a LF generator, a RF oscillator and two PA blocks. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 28 Fig 22.21: ILS Block Diagram (Low Freq Generator) LF 1576A 96. The LF generator contains the circuits to generate CSB and SBO (90Hz and 150Hz) and keying (1020Hz) modulating signals. It also contains the identity keyer/ sequencer and interface for DME master or slave keying. A digital signal processor generates all signals ensuring very stable phase and amplitude relations between the modulation signals. 97. All modulation parameters, such as Modulation Balance, Modulation Sum, RF level, SBO attenuation, SBO phase, Ident code and Ident modulation are controlled by this module. The values are stored locally in EEPROM and can be updated from the RMS processor. 98. The same board is used for single and dual frequency systems and for LOC and GP. RF Oscillator OS (LOC) and OS (GP) 99. The RF oscillator uses a synthesizer for easy frequency changes and simple logistics. The frequencies are set with jumpers at the front edge of the board. The board has two outputs for use in dual frequency systems (Course and Clearance). LPA (LOC), GPA (GP Course) and GPA (GP Clearance) 100. The LPA/ GPA amplifies the carrier from the OS board and modulates the LF from the LF board thus generating CSB and SBO power to feed the distribution network. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 29 101. In localizer LPA (Course) generates Course CSB and Course SBO, the other equivalent LPA (Clearance) generates Clearance CSB and Clearance SBO. The CSB power is 25W max adjustable and SBO power is 1.6W max adjustable. 102. In glide path GPA (Course) generates Course CSB and Course SBO. The Course CSB power is 8W max adjustable and the Course SBO power is 0.8W max adjustable. The other GPA (Clearance) generates Clearance CSB only, power being 1W max adjustable. Monitor 103. The ILS has duplicated monitors with inputs for Course Line (CL), Displacement Sensitivity (DS), Near Field (NF), and Clearance (CLR). Both monitors are active but are normally configured so that the ILS will not perform a shutdown before both of them detects an Alarm. 104. Each of the two monitors consists of two modules. 105. For Cat III use, Hot Standby monitoring can be added by using one additional monitor and associated RF couplers and combiners. 106. The design of the monitors ensures a very high integrity due to the use of digital hardware for the alarm comparators and a very simple Fast Fourier filtering with a signal processor. In addition, the monitor is checked by automatic self-tests. Monitor Front End MF (LOC) and MF (GP) 107. The RF signals in to the cabinet are split in two with power dividers and fed to each monitor. The board has input step attenuators that have to be set at installation to compensate for different antenna systems, different output level of transmitter, different cable lengths etc. 108. The demodulator is a temperature compensated AM diode demodulator and the output is a stabilized envelope (baseband) of the incoming signal. The board also comprises a RF level detector that outputs a DC voltage proportional to the RF level on the input. Monitor System MO (LOC AND GP) 109. This is a complicated board that has 5 distinct functions. Analogue Multiplexer 110. Each of the analogue signals from the 4 monitor channels are sampled with the help of a multiplexer. All signals that include a frequency component (baseband signals) are sampled with a frequency of 640Hz. Signals that does not include a frequency component (RF level volt- ages etc.) are sampled with a lower frequency. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 30 Analogue / Digital Converter 111. After the signals have been routed through the multiplexer all samples are converted to a dig- ital word in a 12 bit A/D converter. Signal Processing 112. The digital words representing the samples are then processed in the digital signal processor. The samples for the baseband signals are used to carry out a Fast Fourier Transform analysis that gives us the modulation depth of the 90Hz, 150Hz and 1020Hz (LOC only) signals. 113. These values are then used to calculate the DDM and SDM of the signals. 114. For signals that has now frequency component, an average is calculated. Comparator 115. After the values of the parameters have been found they are compared with the alarm limits. The alarm limits are stored locally on the board in an EEPROM. 116. The output of the board is a continuous data stream with a single bit for each parameter checked. It is either OK or outside the alarm limit set. The alarm limits can be updated from the RMS processor. TCA (LOC & GP), TCA (LOC and GP with Hot Standby monitor) 117. The Transmitter Controller Assembly is the executive controller of the system. It receives alarm information from both Monitor 1 and Monitor 2 (and Standby monitor if used). The board decides which action is necessary to take when an alarm arises. In addition to the signals from the MO 1212A board the TCA 1218A checks the status of the local front panel switches and the information from the remote control before action is taken. 118. The board is made completely with digital hardware circuits to ensure the highest integrity. The local control and status indicators are a part of the board. RMS (LOC and GP) 119. The RMS unit contains a microprocessor. It is connected to almost all the other boards in the cabinet and reads built-in-test-points from each board. It handles storage and read-out of monitor parameters, measurements for maintenance and fault finding, and performs fault analysis to isolate faults to line replaceable units. It is also used to set monitor limits and transmitter adjustments. 120. The RMS board handles communication to local and remote RMM computers, and in addition it handles the small local display and keyboard for parameter setting and read- out. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 31 121. All Warnings (Pre-alarms) in the system are generated by the RMA-board. 122. Even if the board is U/S the system can operate due to that the MF-MO-TCA chain controls all critical alarm parameters. In such an instance, all Warnings will be activated and it is no longer possible to read or change any limits. OTHER BOARDS PS (LOC and GP) 123. The two DC/DC converters operate in parallel, the outputs are wired-OR with help of diodes, and provides the modules in the cabinet with the following DC voltages: -15V, +5V, +8.5V, +15V 124. In addition the PS-board includes relays that turn off the voltage to the power amplifier stage in the transmitter in case of a Terminator alarm. Change Over section: 125. The section contains the coaxial relays making it possible to change between TX1 and TX2 hence the name. The local RMM connector (standard RS232) and BNC test points for the radiated CSB course and clearance signals are found on the front of the section. CI 1210A (LOC and GP) 126. Opening the door of the cabinet reveals one or several boards mounted at the back. The board that is always there is the interface board of the cabinet. Most of the Signals to/from the cabinet pass through this board. The board contains zener diode protection for all inputs/out- puts. It also carries some jumpers for configuration settings. This board will still carry voltage even if the two circuit breakers in the top front of the cabinet are deactivated. To carry out maintenance on this board or to change any of its configurations, please note the label on the cover that states: Fig 22.22: CI 1210A board GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 32 BW 1566A (LOC and GP - Hot Standby equipment): 127. The BW 1566A is used in hot standby equipment with dual battery banks to provide the following features: (a) Battery protection for the additional battery bank (b) Voltage and current measurements for the additional battery bank (c) Low battery warning for both battery banks (d) Modem power Connection Interface Board CI 1748A and PC 1749A (LOC and GP) 128. The CI 1748A Connection Interface (CI) module unit provides a connection point for all signals except RF signal and high current signals into to the ILS cabinet. The CI module is located in the rear of the ILS cabinet. The CI module is used together with one or two PC1749 modules that handles the power input and associated signals. This board will still carry voltage even if the two circuit breakers in the top front of the cabinet are deactivated. To carry out maintenance on these boards or to change any of its configurations, please note the label on the cover. 129. The CI module is one circuit board with the following blocks. (a) DME interface (b) Analogue multiplexer (c) USB to serial converter (d) RS-232 drivers and receivers (e) Micro controller (f) Modem (g) Shift registers (h) LEDs (i) Configuration (j) Connectors 130. The main task of the CI module is to provide connection points for external signal for the ILS cabinet. It interfaces the external signals (voltages) to levels that can be handled by the internal modules in the cabinet. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 33 131. The Connection Interface also formats serial data to and from the remote control depending on the configuration. The RC data to/from the TX control is always routed through the micro controller on the CI module, and then to the internal or external modem. If configured, the micro controller will include RMM data from the RMS and RC data in the same data stream. If not configured, the RMM data will be routed to Remote 1. Depending on the configuration different formats on the data and bit rates will be selected. Fig 22.23: CI 1748A and PC 1749A MB 1575A (LOC and GP) 132. MB 1575A is the backplane for the 19" sub-rack in the NORMARC 70xxB cabinet. MB 1575A is a passive motherboard that provides all interconnections between the printed circuit board in this sub-rack and all interface for external signals except from RF (Coax) cabling. External AC/DC converter (LOC and GP): 133. The cabinet is supplied with +27V from two external switch mode power supplies that operate in parallel. The two power supplies are configured for load sharing. They have an adjustment potentiometer to allow from 20 - 29.5VDC adjustment of the output voltage. This is a factory adjustment, and should be adjusted to 26.8VDC.The supplies also include alarm circuits that will send a warning to the ILS if there is anything wrong with the supplies. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 34 Fig 22.24: NORMARC 7000B with Eltek battery chargers 134. The main advantages with this Power Supply are: (a) Separate Circuit Breaker for Batteries, DC Output(s) and (b) Mains input(s) are now integrated into the Power Supply (c) The batteries are physically installed inside the Power. (d) Supply cabinet and all the wiring is prepared in factory. (e) The Power Supply is a free standing cabinet that can be installed below the ILS cabinet or at any other convenient location inside the shelter (f) Modular design (g) Redundancy of sub-units inside the power supplies (h) Sub-modules inside Power Supply are hot swappable (j) Based on proven COTS units with high MTBF (k) New maintenance free compact batteries with 12 years battery life and front terminals (M6) GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 35 OPERATION OF THE LOCALIZER / GLIDE PATH OPERATION BY LOCAL CONTROL PANEL Cabinet circuit breakers 135. The power on/off switches is two circuit breakers that are located on the top of the cabinet front. Adjacent to the switches are GND sockets for connecting wrist strap to ensure ESD-protected environment when performing maintenance operations. The upper switch removes power from PS1 and TX1. The lower switch removes power from PS2 and TX2. Fig 22.25: Circuit breakers and GND connection Fig 22.26: Local Control Panel GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 36 Service 136. It is used to indicate that the ILS is currently in SERVICE mode of operation. This will also set the remote control to alarm state. 137. Activated by: EXTERNAL SERVICE line forced low (by LF1223A set in service condition), or RMS in access level 2 or 3, or The LOCAL/REMOTE switch is in LOCAL position, or The MANUAL/AUTO switch is in MANUAL position, or MANUAL mode entered from RMS, or Access grant switch on the Remote Control in grant position. Alarm 138. Used to: Indicate that the ILS has detected an alarm condition. 139. Activated by: One or more alarms are present. Warning 140. Used to: Indicate that the ILS has detected one or more warning conditions. 141. Activated by: Warning condition(s) detected by RMS. Fig 22.27: Service, Alarm and Warning Normal: 142. Used to: Indicate that the ILS detects no alarm condition. 143. Activated by: No alarms present. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 37 PARAM (Parameter Warning): 144. Used to: Indicate that there are one or more monitor parameter warnings present. The warnings from the monitor1/ monitor2 are voted before displayed. 145. Activated by: Monitor parameters are outside the warning limits. Fig 22.28: Button for Warning DISAGR (Monitor Disagree): 146 Used to: Indicate that monitor 1 and monitor 2 disagrees on which parameters that are in alarm state. 147. Activated by: Difference in monitor 1/monitor 2 alarm detection. BATT (Battery Warning): 148. Used to: Indicate that the ILS is running using the 27V battery. 149. Activated by: Loss of mains for charging the 27V battery. IDENT Warning: 150. Used to: Indicate that the ident is faulty for LOC. 151. Activated by: Loss of ident Morse coding for LOC, or ident is continuous for LOC. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 38 MAINT (Maintenance Warning): 152. Used to: Indicate that one or more of the maintenance parameter warnings detected. 153. Activated by: One or more maintenance parameters are faulty or outside limits. ST /BY (Standby transmitter on air): 154. Used to: Indicate that coax position directs the standby transmitters to the antenna and the main transmitters to the dummy load. See Figure 3-5 155. Activated by: TX TO AIR differs from transmitter MAIN select. TX to Air TX1/TX2: 156. Used to: Indicate the position of the coax relay. 157. Activated by: Coax relay position. MAIN TX1/TX2: 158. Used to: Indicate which transmitter that is defined as main. 159. Activated by: Main selected position. Fig 22.29: Main Transmitter ON/OFF indicator GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 39 Course TX1/TX2: 160. Used to: Indicate the status of the TX1 and TX2 Course transmitters. If illuminated the transmitter is on. 161. Activated by: Transmitter in "on" state. Fig 22.30: TX1 and TX2 CLR (Clearance) TX1/TX2: 162. Used to : Indicate the status of the TX1 and TX2 Clearance transmitters. If illuminated the transmitter is ON 163. Activated by: Transmitter in "on" state. FRONT PANEL SWITCHES/BUTTONS Local / Remote 164. Used to: Select between REMOTE and LOCAL control. LOCAL position will enable the local controls and access of RMS software in level 2 or 3. LOCAL will cause a service condition and alarm LED on the remote control. Manual /Auto 165. Used to: Select between AUTOMATIC and MANUAL mode of operation. Setting this switch in MANUAL will prevent shutdown with alarm at the monitor. MANUAL position will also cause a service condition and an alarm at the remote control. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 40 Fig 22.31: Local Remote Write Protect 166. Used to: Prevent changing of alarm limits, ILS parameters and 167. Access at RMS level 3. Switch is active in vertical position. Interlock Override 168. Used to: Enable testing when the interlock signal is active. Horizontal position will override the signal and give SERVICE condition (ALARM at remote control) 169. Valid when: The LOCAL/REMOTE switch is in LOCA and the MANUAL/AUTO switch is in MANUAL. ON/OFF: 170. Used to: Toggle the ILS transmitters on/off. 171. Valid when: The LOCAL/REMOTE is in LOCAL position. The interlock signal must be overridden or not active. Changeover 172. Used to: Toggle TX1/TX2 to antenna system 173. Valid when: LOCAL/REMOTE switch is in LOCAL. MANUAL/AUTO switch is MANUAL MAIN SELECT: 174. Used to: Toggle between TX1 and TX2 as the main transmitter. 175. Valid when: The LOCAL/REMOTE must be in LOCAL position. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 41 Course TX1/TX2: 176. Used to: Toggle the COURSE TX1/TX2 ON/OFF. 177. Valid when: The LOCAL/REMOTE is in LOCAL position. 178. MANUAL/AUTO switch is in MANUAL position. The interlock signal must be overridden or not active. Fig 22.32: Course TX1/TX2 CLR TX1/TX2: 179. Used to: Toggle the CLEARANCE TX1/TX2 on/off. 180. Valid when: The LOCAL/REMOTE is in LOCAL position. MANUAL/AUTO switch is in MANUAL position. The interlock signal must be overridden or not active. Operate Local RMS Panel: Fig 22.33: RMS front panel, with a top level menu screen GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 42 Navigate The Menus (Top Level Menu): 181. The front panel menu system includes a 20 x 4 character LCD and seven push buttons. The buttons are used to navigate in the menus displayed on the LCD and to control/adjust various parameters. A typical top-level LCD screen is shown above. This screen is displayed when the ILS is powered on. (a) Line 1: NORMARC ILS type description or, optionally, a user specified station identification. The station identification can be entered via the RMM software. (b) Line 2: If the ILS is configured for interlock operation, this line shows the status of the inter- lock input on the remote control unit, or "interlock override" if interlock has been over- ridden. The displayed text will be "LOC/GP deselected" or "LOC/GP selected depending on whether the interlock input is respectively active or not. (c) Line 3: Shows the status of the LOCAL/REMOTE switch and the auto/manual state of the ILS. Note that this state not necessarily is the same as the AUTO/MANUAL switch position (the ILS may be set in manual mode with this switch or via the RMM software by logging at access level 2 or higher). (d) Line 4: The last line shows one or two fields, the Remote Control link status ("RC OK" or "RC err") and "Acc.grant" if remote RMM access is granted from the remote control unit. 182. Pressing ESC when the top-level menu screen is displayed will bring up the main menu. Limitations/Specialties of the RMS panel: 183. Some of the RMS options are unavailable in the front panel. (a) Event log (b) Historical data. (c) Administration of users and passwords (d) Diagnostic (e) Change of ILS time and date (f) Two features are only accessible from the RMS panel. (g) Reset historical storage (h) Set IDENT speaker to sound the Morse code GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 43 OPERATION OF ILS USING RMS PC and Modem: 184. The main operator interface is locally or remotely connected personal computers, running dedicated SW and communicating with the main cabinet resident SW via a dedicated proto- col. The system facilitates three channels for PC connections. The Local channel can be connected to a local PC by USB or a serial link. Remote channel 1 can be multiplexed with the remote control data and transmitted to the Remote Control through internal or external leased line modems. The remote PC can then be connected to the Remote Control shelf. Alternatively, Remote 1 can be separately connected to a PC through external modems or a serial link. Remote 2 can be connected to a PC through external leased line or dialup modems. All three PC‟s can be logged on simultaneously, but only one of them can have write access at a given point in time. Fig 22.34: RMS Block Diagram GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 44 REMOTE MAINTENANCE MONITORING SYSTEM (RMMS) RMS Data bus 185. The main operation of the RMS parallel data bus is continuously to collect data from the monitor MO 1212A. Additional functions are setting of monitor alarm limits, delays on MO 1212A, setting of TX-parameters on LF-generator LF 1223A, and reading of system status from the TX Control Assembly TCA 1218A/B. Writing of warning status to the TCA 1218A/B is also done via the RMS data bus. Maintenance Data Collection: 186. In order to facilitate fault isolation and presentation, several analogue and digital measuring points are distributed throughout the system. These points are primarily accessed via the IIC serial bus. In addition, 24 ADC-channels are read directly into the RMA 1215A board. The IIC serial bus collects digital status information from MF 1211A, MO 1212A, LF 1223A, OS 1221A and the CI 1210A connection interface card. 6 of these are user configurable inputs/outputs. In addition, analogue measurements are obtained from the LOC - Power Assemblies LPA 1230A. 187. The ADC-channels are mainly used to measure power amplifier current consumption, as well as system voltages. These measurements are obtained from the Power Supply boards. PS 1227. In addition system current consumption, as well as several user configurable inputs, are measured on the CI 1210A board. Describe the Historical Information Being Stored: 188. Monitor and maintenance measurements are stored in RMA 1215 as historical data. This information is not lost during a power down of the system or if the RMA1215 card is taken out of the system due to a small backup battery on the RMA1215 board. 189. The following types of data are stored in the ILS and can be downloaded to PC Medium time Downloaded data being stored in Download must be periodic the database of the RMM sw started manually Long time Downloaded data being stored in Download must be periodic the database of the RMM sw started manually Warning stor- Downloaded data being stored as Download must be age separate xml-file on PC started manually Alarm storage Downloaded data being stored as Download must be separate xml-file on PC started manually GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 45 Event storage Downloaded data being Downloads new events stored in the database of as soon as connection to the RMM sw station is established Operational Downloaded data being Extracts the important history stored in the database of events from Event the RMM sw storage Events: 190. The following table lists the events generated by the RMS software. Event text Event Description user Access grant Remote The access grant switch was operated. [OFF|ON] Auto Chg Over System A transmitter changeover was performed due to [TX1|TX2] to alarms on monitor parameters. Auto Shut Down System A transmitter shutdown was performed due to frm [TX1|TX2] alarms on monitor parameters. Batt. warning System The system has started or stopped operating [off] from batteries. Change Over to Remote A transmitter changeover was performed [TX1|TX2] from the remote control. Shut Down from System A shutdown of the transmitter that was on-air [TX1|TX2] was performed due to monitor alarms. Change Over to System A transmitter changeover was performed due [TX1|TX2] to monitor alarms. Disagr. warning System Monitor 1&2 disagrees about which [off] parameters are in warning state. Ident. warning System A monitor 1&2 ident parameter has entered [off] or left warning state. Int Tst: 27V not System The RMS verifies that the 27V input on each off power amplifier assembly is below 2 volt. Int Tst: OSC not System The RMS verifies that the COU and CLR off output level maintenance measurements on the OS boards are below the warning limit. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 46 Int Tst: No RF System The RMS verifies that monitor 1 and 2 reports alarm alarm status on CL RF and CLR RF monitor parameters 30 seconds after the turn-off command. Lost RC System The transmitters turned off because no data Shutdown was received from the remote control unit. Operational history 191. Selecting ILS-Data Operational history will bring up a list of operational history entries that have been downloaded from the ILS and stored in the database on the PC. All new entries are downloaded on each login to the ILS. The last 100 entries are stored in the ILS, while the last 2500 events may be viewed in the RMM. The database file on the PC may contain several thousands of entries for each ILS station. 192. There are 3 types of entries shown in the list. These are: 193. "Clear history". This entry is placed in the history list after a user has selected to clear all operational history and if the RMS detect that the data stored in the battery backed RAM is not valid. The last case may be the case after an upgrade to a new RMS version if the layout the RAM has changed between RMS versions. 194. "Monthly report". The RMS stores this entry on the first day of each month. Since the operational time counter (hours) is also stored, this gives the user information about the usage of the ILS the last month. 195. "Alarm shutdown". This entry indicated that the ILS has performed a transmitter shutdown due to an alarm condition detected by the executive monitors. Remote Control System 196. Each LLZ or GP Sub System is equipped with an RCA 1750 Remote control unit consisting of an RC 1752A Remote control board and RF 1751A front panel. The Remote control units provide the user interface to the ILS cabinet from the control tower or technical equipment room. The remote control will be connected with the ILS cabinet using an OFC link. Input from the front panel switches such as ON/OFF, Change over and access grant are same to the IULS cabinet, and ILS status and other information is received and displayed all LED indicators. An additional slave panel SP 1754 is available for use in the control tower. The front panels are shown in the figure below, GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 47 Remote Maintenance Monitoring (RMM) 197. Comprehensive RMM functions are available on locally or remotely connected PCs with NORMARC 7000 and NORMARC 7050 RMM software. Fig 22.35: Front panel for the Remote Control RCA 1750 (left) and the Slave Panel SP 1754 (right) RMM SOFTWARE Overview of the NORMARC 7000 RMM 198. The NORMARC®7000 RMM is a Microsoft Windows based program that provides access to all the data and functions made available by the ILS remote monitoring subsystem. By connecting to the ILS remote monitoring subsystem, the program lets the user do the following: (a) View the current status and measurements done by the ILS. (b) Configure ILS monitor and transmitter settings. (c) View reports that shows the current operational status and configuration of an ILS. (d) Download historical data from the ILS and browse through individual data sets. (e) Download and view events to see the operational history of the ILS. (f) Connect to the ILS with a null modem cable (direct),dial-up connection or leased line connection. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 48 Reliability and Continuity of Service 199. The reliability analysis is done accordance with MIL-HDBK-217F, Part Stress Analysis. To determine the failure rate of the modules, the following conditions are defined: (a) Ambient temperature : 30°C (b) Environment: Ground, Fixed (c) Part quality factor as procured/ specified by the part supplier 200. For operational and safety consideration, the Mean Time Between Outages (MTBO) is of prime interest, as this term expresses the mean time between loss of a proper navigation signal. The Mean Time Between Failure (MTBF) is interesting for logistic purposes as it expresses how often modules will have to be repaired or replaced. Definitions Of Continuity Of Service And Mean Time Between Outages 201. The continuity of service is defined as the probability that the ILS equipment continues to radiate the guidance signal during a specified time interval. The time interval is the critical time during a landing and is 15 seconds for Level 2, 3 and 4(GP) 30 seconds for Level 4(LLZ) ICAO Annex 10 (Table C-2) gives the performance objective for Integrity and Continuity of Service (C.O.S.) in the ILS classification system in Level 1, 2,3 and 4. Level 2 is the performance objective for CAT I, Level 3 for CAT II and CAT IIIA and Level 4 for CATIIIB/C. Calculation of C.O.S. / MTBO 202. The C.O.S. figures are based on no outages of signal-in-space during a time period of 30 seconds, which is required for level 4 LOC performances. In addition to C.O.S. / MTBO figures for the total system in operation, calculations are done for the system operating with one faulty transmitter, with one faulty monitor, and with faults on both one monitor and with faults on both one monitor and one transmitter. Below follows the equations for the MTBO for the different system states: Calculation of MTBF 203. The mean time between failures for the entire system is inverse proportional to the sum of the failure rates to every module in the system. This can be associated with all modules connected in series and will therefore be referred to as MTBFSerial. The MTBF- figures are dependent of system configuration and for hot standby system having 24 antenna elements, it is: MTBF Serial =4530 Hours. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 49 Conclusion 204. The NORMARC 7014/7034 – Hot Standby, Two frequencies LOC/GP System will satisfy the Continuity of Service (C.O.S.)/MTBO requirement for ICAO Level 4 ILS. These requirements will be satisfied even with a faulty transmitter and a faulty monitor. Availability 205. Availability is calculated based on yearly downtime caused by scheduled and unscheduled maintenance. Scheduled maintenance LOC and GP Cat II: Maintenance man-hours and downtime are shown in table below: Maintenance Man-hours (hours) Down-time (hours) Weekly-monthly * Quarterly ** 1 0 Half-yearly 0.5 0.5 Yearly 3 2 Total 8 3 * Weekly to monthly visits recommended for visual inspection of site. ** Use of FFM assumed for Cat II, if FFM is not used, the quarterly inspection must be reduced to monthly for Cat II. UNSCHEDULED MAINTENANCE MTTR 206. Based on the MTBF figures, a system (LOC or GP) has a logistic MTBF of approx. 5,000 hours, giving 1.7 failures per year. Of those, 10% to 20% will lead to an outage, while the rest is non-critical. Field data for the equipment gives a far higher MTBF of more than 15000 hours, reducing the probability of unscheduled maintenance even further. With a Mean Time To Repair (MTTR) of 20 min. this gives a direct repair time of less than 2 hrs. per year, plus transport time etc. dependent on local conditions combined for LOC and GP. The logistic delay is only relevant for failures that result in outages and can be neglected for Cat I/II systems. A typical value could be 6 hours, giving a yearly- unscheduled Cat III unavailability (mostly reduction to Cat I/II) of 10 hours. Criticality Levels 207. The Criticality Levels of ILS are as follows: (a) No effects on signal performance beyond monitor alarm limits or monitor system. (b) Monitor alarm initiated and TX OFF. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 50 (c) Monitor alarm initiated, TX not switched OFF if this failure in addition to other failures of same criticality. (d) Monitor alarm initiated, TX not switched OFF. (e) No monitor alarm, TX not switched OFF. ILS CRITICAL AND SENSITIVE AREA CAT II AND CAT III Localizer Sensitive Area 208. The localizer Sensitive Area (SA) calculation is based on computer analysis using the localizer program AXIS. AXIS is using the same formulae as the GEC- Marconi VLOC has been confirmed on UNITED KINGDOM GOVRNMENT CONTRACTS and on work for the UK CAA. 209. The definition of the localizer SA is that inside this area a B747 a/c on the ground could produce a beam- bend larger than 4 µA for another a/c on approach between ILS point B and E. 210. The B747 is modeled with its tail fin as a vertical metal sheet, 5.7 m above ground level, 13.6 m high and 8 m wide. The a/c is rotated 360 degree in 45 degree steps to take care of the a/c orientation at the inlets and outlets plus at holding points. 211. It is assumed that the static beam- bends are max 3 µA, as the static and dynamic bends are added on a root sum square combination (refer ICAO Annex 10 attachment C Paragraph. 2.1.10.5.1). 212. The course sector used is 4.0 deg. For other Course Sectors, the width of the SA will reduce in proportions with the square root of the ratio between the Course Sectors. 213. Please note that this is a theoretical calculation of the SA. It is up to the authority to determine the actual SA for a specific airport. Then local conditions have to be taken into account. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 51 Fig 22.32: Typical LOC site Localizer Critical Area 214. The Localizer Critical Area for all antenna system types is given in the figure below. No persons or vehicles are allowed to intrude this area during an ILS approach; this applies for Cat I also. Glide Path Sensitive and Critical Area 215. The glide path site may be located on either side of the runway, but the most reliable operation will be obtained if the site is selected on terrain least obstructed by taxiways, aircraft holding aprons, parking ramps, buildings, power lines etc. The site should offer the widest area of smooth ground with possibilities of leveling without excessive physical or economical effort, if indeed leveling is deemed necessary. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 52 Fig 22.33: Typical Glide Path Critical and Sensitive Area 216. The glide path antenna system should be located at a distance of 75-200 m from the runway Centre line. The distance from the runway threshold is a function of several factors upon which establishment of the optimum operational conditions depend. These factors are: (a) The glide path angle (b) Threshold crossing height requirements (c) Obstruction clearance requirements (d) The slope of the terrain in front of the antenna system GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 53 (e) The extent of smooth terrain in the site area and beyond the threshold Fig 22.34: Typical Glide PATH Site Introduction to the NORMARC 7710 NAV Analyzer 217. The NORMARC 7710 NAV Analyzer is used to adjust, verify and record parameters of ILS (Localizer, Glide Path, Marker Beacon) and VOR ground systems. The NAV Analyser‟s functionality substitutes instruments like ILS/VOR receivers, modulation meters and frequency counters. It incorporates all ILS and VOR channels selectable without any tuning or equipment changes. It facilitates measurement of (a) ILS: Modulation Depth (DDM and SDM), RF level and Ident modulation level, Carrier and Audio frequencies, 90Hz to 150Hz phase and harmonic distortion, Ident decoding. (b) Marker: Depth of modulation, Modulation frequency, RF level, Carrier frequency. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 54 (c) VOR: Bearing, Depth of modulation 30Hz, Depth of modulation 9960Hz, Ident modulation, RF level, Frequency modulation index, Carrier frequency, subcarrier frequency, Ident decoding. 218. The NAV Analyzer is a portable, battery-operated weatherproof unit to be used outdoors, in a vehicle or inside the equipment shelter. It is supplied with a dipole antenna with a unipod support and coaxial cable. The analyzer has a rough outdoor design and is protected against damage during transport. 219. The NAV Analyzer uses a digital radio with demodulation based on digital signal processing and with storage functions. Full control from a remote system (typically a PC) by use of network technology is possible. 220. The user interface is a graphical display (GUI) with a corresponding keyboard on the front panel of the instrument. Night condition is supported. Audio jack for Identity / Voice monitoring is incorporated. It has a GPS and tachometer interface for ILS Localizer runway measurements. Fig 22.35: Rear Panel of Nav Analyzer 7710 Fig 22.36: Front Panel of Nav Analyzer 7710 GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 55 Fault Analysis (a) Monitor warning tests: This test can be done by the RMM software for automatically diagnosing faults that result in monitor 1 and 2 warning indications. Flow Chart 22.1: Monitor warning Test (b) Changeover without shutdown: The RMM software uses the maximum configured monitor alarm delay to determine whether a changeover alarm is followed by a shut- down. If no shutdown alarm event occurred within the maximum configured alarm delay after the changeover alarm event this algorithm will be used. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 56 Flow Chart 22.2: Diagnosing a changeover-only alarm (c) Changeover with subsequent shutdown: A changeover alarm event that is followed by a shutdown alarm event within the maximum configured monitor delay will be diagnosed as described in this section. The algorithm used depends on the voting configuration. The algorithm is based on the fact that a fault (in a 2/2 voting system) which causes a complete shutdown, must be some point that is common for the transmitter section and the monitoring section. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 57 Flow Chart 22.3: Diagnosing changeover/shutdown alarms GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 58 (d) Maintenance warnings without follow-errors: A maintenance warning on a board listed in the following table indicates that there is a fault on that board. Board LF generator 1 or 2 Oscillator 1 or 2 RMS board Monitor 1 or 2 TX Control board User defined inputs (e) Power amplifier tests: Warnings on a PA implies PA failure if there is no warning or error on the corresponding OS or LF. The algorithm assumes that a warning indication on any of the measurements on a PA means there is a failure on this PA, if the corresponding OS and LF have no maintenance warning indications. (A fault on the OS and LF may cause a warning on the PA.) (f) Monitor 1 and 2 Front End Tests: Warning on monitor frontend 1 implies monitor frontend 1 failure if there is no warning on monitor frontend 2 and vice versa. The maintenance measurements from the monitor frontend boards will be affected by the monitor input signals, i.e. the diagnostic algorithm cannot use these measurements alone to reliably diagnose fault on the monitor frontend boards. The algorithm assumes that both frontends are fed the same input signals. If a maintenance warning then exists on one, but not both of the boards, this board is assumed to be faulty. If maintenance warnings exist on both boards no knowledge is gained about monitor frontend health status. (g) Remote control tests: If there is a “RC link status” warning, there is a problem with the remote control or its data link. A warning on the RC link status indicates that the TXC does not receive valid data from the remote control unit. (h) Monitor DC-loop alarm: If both monitor 1 and monitor 2 reports DC-loop alarms or warnings the antenna has a broken element. (j) Transmitter control tests: TX control “EPROM check” or “Integrity check” warnings indicate a failure on the TXC board. (k) Standby monitor tests: If there is a warning on the standby monitor board this board is faulty. (l) Standby Monitor Front End Tests: If there is a warning on the standby monitor frontend board and there is no warning or alarm indication on the standby monitor measurements then the standby monitor frontend board is faulty. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 59 EXERCISE Objective Q1. Fill in the blanks (a) The frequency range of Localizer is ____ to ______MHz. (b) The number of PA units in ILS cabinet are______. (c) No of antenna arrays in Localizer are ________. (d) Input power supply required for Glide path is ______. (e) The Glide path varies from _____ to _____ degrees. Subjective Q2. What are the various units of ILS? Q3. Write down definition of the following:- (a) Decision height. (b) Course Line of ILS. (c) Course Sector of ILS. (d) Displacement Sensitivity of LLZ. Q4. Explain LPDA antenna system of LLZ. Q5. Define SDM and DDM. LIST OF ABBREVIATIONS AC Alternating Current ADC Analog to Digital Converter AGC Automatic Gain Control CL Course Line CLR Clearance COU Course CPU Central Processing Unit CS Course Sector DAC Digital to Analog Converter GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 60 DC Direct Current DDM Difference in Depth of Modulation DF Difference Frequency DL DC Loop DS Displacement Sensitivity DSP Digital Signal Processor EEPROM Electrically Erasable Programmable Read Only Memory EMC Electro Magnetic Compatibility EMI Electro Magnetic Interference EPROM Erasable Programmable Read Only Memory FFT Fast Fourier Transform FIFO First-In-First-Out FPGA Field Programmable Gate Array GPA Glide Path Power amplifier Assembly I/F Interface I²C Inter Integrated Circuit IIC Same as I²C ILS Instrument Landing System LED Light Emitting Diode LF Low Frequency LOC Localizer LPA Localizer Power amplifier Assembly LRU Line Replaceable Unit MCU Monitor Combiner Unit NAV Navigation signals NF Near Field PC Personal Computer RAM Random Access Memory RF Radio Frequency RMM Remote Maintenance Monitor RMS Remote Monitoring System GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 61 ROM Read Only Memory RTC Real Time Clock SC Station Control SDM Sum in Depth of Modulation SPA Same Parameter Alarm SRAM Static Random Access Memory STB Standby SW Software TRM Terminator TX Transmitter ----------------------------------------------------------------------------------------------------------------- References 1. User Hand Book and Operator‟s Manual 2. Technical Manual Part-I 3. Technical Manual Part-II 4. Technical Manual Part-III GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 62 GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 63 CHAPTER - 23 DOPPLER VHF OMNI RANGE (DVOR): NORMARC 6512 Introduction 1. VOR (VHF-Omni directional Radio Range) is a radio navigation aid installed at a reference point on an airway or an airport that provides magnetic bearing of the location of an aircraft in reference to the reference point, and utilizes the frequency band between 108 to 118 MHz. VOR is an ICAO standardized en-route navigation system. Fig 23.1: DVOR Pictorial View 2. In order for an aircraft to recognize its own magnetic bearing, VOR radiates both a variable phase signal and reference phase signal, where the phase of the former depends on the bearing of radiation, while that of the latter is constant regardless of the bearing. An aircraft flying within the range of a VOR can determine its own bearing by measuring the phase difference between the variable phase signal and reference phase signal. 3. The phases of reference phase signal and variable phase signals are identical when they are received at a position that is located in the direction of magnetic north in GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 64 reference to the VOR. When changing the receiving point clockwise about the VOR, the phase of variable phase signal is delayed relative to the reference phase signal and the delay comes to 360 degrees when the point makes a clockwise full turn about the VOR. Assuming that there is no error on the information from the VOR station, the angular difference of the receiving point corresponds to the delay in phase, thus accurate bearing information can be provided to the aircraft. 4. DVOR (Doppler VOR) is a VOR that utilizes Doppler effect for bearing information signals and transmits the reference phase signal and variable phase signal in amplitude modulation (AM) and frequency modulation (FM) signals respectively. In addition to bearing information signals, ID and voice signals are also transmitted to aircraft. LCD TOUCH PANEL FRONT DOOR LOCK Fig 23.2: DVOR Equipment Rack GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 65 CONTROLLER SHELF BREAKER PANEL & LED BUTTONS TRANSMITTER 1 CHANGE OVER UNIT TRANSMITTER 2 Fig 23.3: DVOR Equipment Rack 5. The features of the DVOR are as follows: (a) The DVOR System uses a DSB system that transmits the variable phase signal with double side bands (DSB). (b) The DVOR can be used for both airports and airways and operated alone or in conjunction with a DME. ID signals are generally provided from the DVOR to the DME, while transmission from DME to DVOR is also selectable. (c) Dual configured transmitter and power supply system ensure continuous operations by automatically switching the system in operation with the other in stand- by mode if a malfunction takes place in the operating system. The stand-by system can be checked and units replaced without ceasing the operation of the DVOR. (d) It is possible to repair the DVOR in quite short time, because each module can be easily exchanged from the front. GCRNA WITH MAFI RESTRICTED AIRMEN  RESTRICTED 66 (e) The DVOR can be operated continuously on a 24-hour basis. (f) The DVOR is a compact, inexpensive, reliable, state-of-the-art equipment using latest digital technologies. (g) The DVOR is equipped with a PC for maintenance purpose (RCMS), which monitors the operating conditions and estimates the defective modules. This PC can also concurrently manage a DME. (h) The DVOR allows simple channel changes with a synthesizer and easy parameter setting from the PC for maintenance purposes (RCMS). (j) An edge monitor system in which a field monitor antenna is installed at the counterpoise edge is optional. (k) On-line technical support from a maintenance facility is optional. 6. Principle of operation: VOR systems provide airborne VOR receivers with bearing information comprised of the following two modulated signals with the same frequency: (a) Reference phase signal:-30 Hz signal with a constant phase in relation to all VOR directions (b) Variable phase signal:-30 Hz signal with a specific phase difference in reference to the reference phase signal depending on the receiver direction The phases of the reference phase signal and the variable phase signals are identical when they are received at a position that is located in the direction of magnetic north in reference to the VOR. When changing the receiving point clockwise from the VOR, the phase of the variable phase signal is delayed relative to the reference phase signal, and the delay comes to 360 degrees, when the receiver makes a full clockwise turn around the VOR. 7. Assuming that there is no error in the information from the DVOR station, the angular difference of the receiving point corresponds to the delay in phase, thus accurate bearing information can be provided to the aircraft. 8. In a DVOR system, the bearing information signal, i.e. the variable phase signal and the reference phase signal ar