ILS Part 1 PDF

1 Chapter 3 INSTRUMENT LANDING SYSTEM & VHF OMNI RANGE  2 Introduction In order to be able to land the aircraft frequently in bad weather where pilot can’t see runway of the airport by any means requires electronic aid to the p...

1 Chapter 3 INSTRUMENT LANDING SYSTEM & VHF OMNI RANGE  2 Introduction In order to be able to land the aircraft frequently in bad weather where pilot can’t see runway of the airport by any means requires electronic aid to the pilot This electronic aid is nothing but Instrument Landing System (ILS) was developed at the end of the Second World War, which provides greater precision guidance for the aircraft to land on the selected runway  3 Aeronautical VHF Band VHF Navigation VHF Communication 108 MHz 118 MHz 136 MHz  4 Learning Outcomes  Working of ILS System  ILS Aircraft Equipment  ILS Airborne Loading  Working of VOR System  VOR Aircraft Equipment  VOR Airborne Loading  Principle of Automatic Flight Control (Auto pilot)  5 Working Principle of Instrument Landing System (ILS) ILS ground system consists pair of antennas transmitting  Localizer (LOC)  Glideslope (G/S) beams directed close to either side of the ideal approach path  6 International Civil Aviation Organisation (ICAO) Visibility Categories Runway CATEGORY Visual Range (RVR) I 800 m (2600 ft) II* 400 m (1200 ft) III 200 m (700 ft) * Also equipment should be certified as Category II  7 Localizer/Glideslope frequency pairing in MHz Localiser Glide Localiser Glide Localiser Glide Localiser Glide slope slope slope slope 108.10 334.70 109.10 331.40 110.10 334.40 111.10 331.70 108.15 334.55 109.15 331.25 110.15 334.25 111.15 331.55 108.30 334.10 109.30 332.00 110.30 335.00 111.30 332.30 108.35 333.95 109.35 331.85 110.35 334.85 111.35 332.15 108.50 329.90 109.50 332.60 110.50 329.60 111.50 332.90 108.55 329.75 109.55 332.45 110.55 329.45 111.55 332.75 108.70 330.50 109.70 333.20 110.70 330.20 111.70 333.50 108.75 330.35 109.75 333.05 110.75 330.05 111.75 333.35 108.90 329.30 109.90 333.80 110.90 330.80 111.90 331.10 108.95 329.15 109.95 333.65 110.95 330.65 111.95 330.95  8 Changi Airport ILS CAT-II Runways  9 Localizer  Localizer transmits signals in the VHF band between 108.10 to 111.95 MHz, using the first odd decimals with a channel spacing of 50 kHz  Localizer produces two directional beams on the left and right sides of airport runway centre line  Both these left, right beams are modulated with 90Hz and 150Hz signals respectively  10 Examine two cases:  In case one, if an airplane is located on the left side of course path, the 90 Hz signal dominates and localizer indicators on board deflected to the right indicating the runway centreline is to the right  In case two, if an airplane is located on the right side of course path, the 150 Hz signal dominates and localizer indicators on board deflected to the left indicating the runway centreline is to the left  11 LOCALIZER CARRIER FREQUENCIES: 108.10 MHz TO 111.95 MHz 1º LOCALIZER DEVIATION = 75 µAmps RECEIVER OUTPUT 90Hz AMLITUDE A RUNWAY MODULATION LOCALIZER 90Hz AMLITUDE TRANSMITTER MODULATION D B 150Hz AMLITUDE MODULATION C 150Hz AMLITUDE MODULATION A FLY RIGHT FLY LEFT C B ON DOT LINE FLY LEFT D  12 Coverage of localizer beams are within 10º of runway centre line out to 25 nm, within 35º of runway centre line out to 17nm 17 nm 25º 10º R/W- C/L 25 nm LOC ANTENNA 10º 17 nm 25º  13 LOC ANTENNA  14 Glideslope  Glideslope transmits signals in the UHF band between 329.5 to 335.0 MHz, with a channel spacing of 150 kHz  Pilot selection of required localizer frequency on the controller will cause both localizer and glideslope receiver’s tune to the appropriate paired frequencies  Glideslope produces two directional beams one above the other, upper beam is modulated with 90Hz and lower beam is modulated with 150Hz signals respectively  15 Examine two cases:  In case one, if an airplane is located above the glideslope, the 90 Hz signal dominates and glideslope indicators on board deflected down indicating glideslope is below the aircraft  In case two, if an airplane is located below the glideslope, the 150 Hz signal dominates and glideslope indicators on board deflected up indicating glideslope is above the aircraft  16 GLIDE SLOPE CARRIER FREQUENCIES: 329.5MHz TO 335.0MHz 0.35º GLIDE SLOPE DEVIATION = 75 µAmps RECEIVER OUTPUT A 90Hz AMLITUDE B MODULATION C GLIDE SLOPE TRANSMITTER A FLY DOWN C FLY UP B ON DOT LINE 150Hz AMLITUDE MODULATION RUNWAY  17 Glideslope beams covers over a vertical angles of between 1.35º and 5.25º out to 10nm 5.25º 3º 1.35º G/S ANTENNA  18 G/S ANTENNA 19  20 Example 3-1  Find the harmonics present in 90 Hz and 150 Hz tones 150 + 90 = 240 Hz 150 – 90 = 60 Hz  21 Example 3-2  What rate of descent should an aircraft use on 30 ILS glideslope if it has a ground speed of 120 knots? 10 100 ft 6000 ft 1 nm  6000 ft 1 10   6000 ft  100 ft / nm 60 30  300 ft / nm Rate of descent  300 ft / nm  120 nm / h 300  120   600 ft / min 60 22 23  24 ILS Aircraft Equipment ILS aircraft equipment consists of  Receivers In ILS operation there will be two receivers, a VHF localizer receiver and a UHF glideslope receiver. Both these receivers are operated from the same unit for easier functionality  Control unit The pilot should first tune the required ILS localizer frequency and identify the station from the audio signal, then localizer signal will give an indication of the aircraft position in relation to the runway  25 G/S ANTENNA RECEIVER VOR/LOC INDICATOR ANTENNA CONTROL UNIT ILS Aircraft Equipment  26 COMM NAV 118.00 108.00 VOR Control Unit  27  ILS indicators ILS signals are often displayed to a conventional or electronic indicators, most modern aircrafts uses Attitude Direction Indicator (ADI) for ILS landing In ADI the localizer drives a rising runway laterally to display deviation while glideslope drives a pointer over a scale  Aerials VHF localizer signals are received by whip antennas on either side of the tail, which may also be used for VOR signal reception The UHF glideslope signals can be received by folded dipole antenna that is located at nose of the aircraft  28 356 20 20 G 10 10 S 163 20 20 LOC Attitude Director Indicator 29 30  31 ILS Airborne Loading  To receive and process the localizer signals, a conventional AM-superhetrodyne receiver is most suitable  The received localizer signal consists of a carrier at VHF band modulated with 90 Hz and 150 Hz tones  Preselector selects required localiser frequency and filter out all other frequency components for high Carrier to Noise ratio (C/N)  After the preselector, signal goes to the mixer where it mixes with synthesiser frequency to produce Intermediate Frequency (IF) signal  32  This IF signal is sent through the detector stage, where 90 Hz and 150 Hz tones are separated from IF carrier signal.  The detected 90 Hz and 150 Hz tones are fed into two different circuits  Monitor circuit checks reliability, quality and deviation instrumentation circuit compares the signal levels of 90 Hz and 150 Hz tones, which produces a difference signal (or Δ delta-signal) between these tones  This Δ signal is applied to the Attitude Director Indicator to drive the horizontal deviation course pointers  GLIDESLOPE LOC/VOR ANTENNA 33 ANTENNA PRESELECTOR PRESELECTOR MIXER GLIDESLOPE LOCALIZER MIXER SYNTHESISER SYNTHESISER GLIDESLOPE TUNE LOCALIZER DETECTOR CONTROL DETECTOR Airborne GLIDESLOPE LOCALIZER Loading DEVIATION DEVIATION INSTRUMENTATION INSTRUMENTATION GLIDESLOPE LOCALIZER MONITOR MONITOR LOC LOC CONTROL UNIT FLAG DEV GS FLAG GS DEV ATTITUDE DIRECTOR INDICATOR  34  Similarly, glideslope receiver works on the same principle as localizer receiver  In glideslope receiver the operating frequency automatically changed to UHF band for glideslope signal requirement  The glideslope deviation instrumentation compares the signal levels of 90 Hz and 150 Hz tones as localizer deviation instrumentation but the produced difference signal is applied to drive the vertical deviation course pointers of Attitude Director Indicator  If the rough track to the aerodrome is known, the pilot can intercept the localizer some distance along it