Glidepath

Glide slope / Glide Path

Is a portion of the ILS that provides the pilot with vertical guidance to the touchdown point of the runway. The GP generates an RF−Signal at frequency range of 328 to 336 MHz and is amplitude modulated with 90 and 150 Hz. The transmitter of GP can be a 2F system or 1F system and both produce 5 W of power. The glide path signal is receivable up to a distance of 10 nautical miles within an azimuthal sector of ±8°relative to the localizer course line with the touch down point as reference and between the elevations 0.30 to 1.75 nominal glide path angle.The GP antenna is installed approximately 286 to 344 m beyond the runway threshold and 120 to180m from the runway centre line. An optional nearfield dipole is installed in the GP radiation sector for monitoring the course position of the GP signal. The position of the dipole depends on the type of installation and on the local conditions as regards the glide angle. The GP transmitter shelter is installed in the vicinity of the GP antenna.

Glidepath or Glideslope also radiates two modulating signal, the 90Hz and 150 Hz. Above the path angle 90Hz is predominant than 150Hz. Below, the 150Hz is predominant than 90Hz, and at path angle the two are equal.

LOCALIZER

LOCALIZER

 

Localizer is a part of ILS that provides the pilot with horizontal guidance towards the airport runway center line.

Operating Frequency Band

  108 – 111.975 MHz

Modulation Frequency

  90 Hz and 150 Hz

DDM

  20% (90 Hz and 150 Hz) Nominal

  18% - 21% allowed for Cat. I and Cat. II

  19% - 21% allowed for  Cat. III

Voice Modulation

  Optional

Identification Signal

  1020 Hz with 5% - 15% Modulation

  keyed 2 – 3 Characters of International Morse Code (audio of 1020 Hz) e.g. I-CIA

Monitoring

  Automatic Monitoring System to designated control locations.

 

Localizer radiates two modulating signals 150Hz and 90Hz. It produce a predominance of 150Hz to the right of the runway centerline as seen by the aircraft and a predominance of 90Hz modulated RF to the left of runway centerline. At centerline the two modulated RF are equal.

Defective Associated Facility Interface (AFI) module of DME

The AFI module is used as interface between the DME ground beacon and an associated VHF equipment to make the emission of the identity code expressed in international Morse code synchronous.This module allows the identification signals to be correctly exchanged between the DME and associated equipment (e.g. VOR, ILS, and MLS equipment). If any, as far as the identity code and the status signals are concerned.

 figure of Defective AFI

We experienced this trouble when the DME equipment shuts down on both system. We checked the system and it found that AFI is defective because of burned out module and LED's in front doesnt blinking at all. The remedy is only buying a new module since all individual components of AFI are surface mounted.

DVOR Trouble

Last year we encountered a DVOR problem in which the Nearfield position RF level is too low that caused an alarm on our two monitors. It shutdowns both system of DVOR. We bypassed the two monitors and check the actual RF level by using a DVOR portable receiver. All the actual reading of data in aerial is the same as per recorded normally in our logbook. We concluded that the equipment is operating normally and the problem is in the monitor dipole section.Through analysis and at the same time reading the equipment manual we decided to troubleshoot at the dipole section of the DVOR. We loosened and tightened back the transmission cable and clean all connectors for possible contamination of rust. The problem still existed, and we then checked the 3dB attenuator if its the caused of the problem. We found available attenuator and changed the existing one and still the problem is just the same. After all the possibility we decided to focused on antenna itself. We brought down the antenna of monitor and we found out that it had made by ants as its habitat and all its holes were contaminated with dirt's. We disassembled the antenna and by used of pressure washer we cleaned thoroughly all the contamination.After cleaning we assembled again the antenna and brought up and all data on RF nearfield level goes back again into normal state.

        figure of Antenna  monitor dipole

Distance Measuring Equipment DME

DME

DME (Distance Measuring Equipment) is a radio aid for short and medium distance navigation. It can allows 100 aircrafts simultaneously to measure their distance from a ground reference (DME transponder). The distance is determined by measuring the propagation delay of a gaussian pulse, which is emitted by the aircraft transmitter and returned by the ground station after reception.DME operates in the frequency range of(960 to 1215 MHz).

Aircraft's airborne interrogator transmit encoded interrogating  pulse pairs on the ground station. The DME station in turn, transmits encoded reply pulse pairs on the air-borne equipment, The real distance information is the time interval between interrogation emission and reply reception. Aircraft's equipped with DME transmit encoded interrogating RF pulse pairs about the beacon's obtaining channel. The beacon, consequently, emits encoded reply pulse pairs about the receiving channel with the air-borne tools, that is 63 MHz apart from the transmitter frequency former.

Time interval among interrogation emission and reply reception provides the aircraft with all the real
distance data through the ground station; this info could be go through from the pilot or even the navigator straight around the airborne indicator. The ground transponder is capable to reply approximately about 200 interrogators at a time (i.e. 4800 pulse pairs/s). Generates random pulse pairs ("squitter") to take care of a minimum PRF of 800 to 2700 pulse pairs per
2nd (programmable) whenever the amount of decoded interrogations is decrease than that.
This reply is obtained and decoded by the airborne receiver, where unique timing circuits automatically measure the lapse between interrogation and reply and convert this measurement into electrical output indicators. The beacon introduces a fixed delay, known as reply delay, among the reception of each encoded interrogating pulse pair and also the transmission of the corresponding reply.