ILS gives pilots a continuous indication of whether the aircraft is left or right of the final approach track and also its position in relation to an ideal glide path to the runway. This information is provided by marker bea-cons, the outer marker at about four miles from touchdown and the middle marker at about 3,500 ft. As the aircraft passes over them they give an audible signal. The outer marker transmits low-toned dashes and the middle marker alternate dots and dashes on a medium tone. These markers cannot only be heard, they also illuminate lamps on the in-strument panel. These signals are transmitted on a standard 75 MHz.
A transmitter with a large aerial system known as the Localizer is situated at the far end of the runway, transmitting its signals on either side of the enterline of the runway and ap-proach. A second unit, the glide path transmitter, is located at the nearer end and slightly to one side of runway. Aboard the aircraft there is an
the globe (Argentina, Australia, Japan, Hawaii, Liberia, North Dakota, Reunion Island, and Tri-nidad) so that aircraft, equipped with a simple re-ceiver and Omega charts can find their position wherever they are.
Omega is a very long range form of Loran.
6. Global Positioning System (GPS)
It is generally considered that GPS is revo-lutionizing aircraft navigation now and will in time replace most existing aids. Based on a series of satellites, it is capable of fixing an aircraft’s po-sition anywhere on the globe with an accuracy of few metres. It is already under trial on certain transoceanic flights and may become the major aid for instrument approaches during the next few years. GPS was originally designed for US military use, the first satellite being launched in 1978. The completed system consists of 24 satel-lites with three on-orbit spares. The master con-trol station is located in Colorado and is sup-ported by monitoring stations on Ascension Isl-and, Diego Garcia, Kwajelein, and Hawaii, spaced at nearly equidistant points around the earth. The
instrument with two needles: one is actuated by satellites require constant attention from the
the signals from the Localizer and moves left and right, while the other, which is operated by the signals from the glide path aerial, moves up and down. When the two needles are crossed at right angles, the aircraft is lined up for a landing. Any deviations can be quickly corrected by an experienced pilot.
ILSs are divided into three categories: Cat 1 – Operation down to 60 m decision height with Runway
Visual Range (RVR) of 800 m.
Cat 2 – Operation down to 30 m decision height with RVR of 400 m.
Cat 3 – Operation with no height limitation to and along the surface of the runway with ex-ternal visual reference during the final phase of landing with RVR of 200 m.
ground, including orbital positioning adjustments. Without this maintenance it is said that the system would ‘ degrade’ in about two weeks!
GPS equipment in the aircraft measures the time that it takes the satellite signal to reach the receiver. To do this accurately, it needs the exact time the signal leaves the satellite. Each satellite carries four atomic clocks to keep unbelievably accurate time. GPS works on the classic naviga-tional principle of triangulation. However, instead of the position being the point at which three lines from different radio beacons intersect, a GPS position is derived from the intersection of three‘ circles’ transmitted from three satellites. The receiver also checks a fourth satellite.
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Also operational is GLONASS, the Global Orbiting Navigation Satellite System developed
Localizer/ DME approaches are non – pre- by Russia. A joint system combining the cision and therefore uncategorized. GLONASS and GPS satellites is planned so that
5. OMEGA worldwide coverage will be increased significantly.
Eight VLF (Very Low Frequency) radio transmitters are situated at strategic points on
© НИЛ НОТ НИО УВАУ ГА(и), 2009 г
Aviation English Fundamentals | 96
Ex. 136. For detailed information read the text again and answer the questions:
1. What is the function of radio beacons? 2. What is the purpose of NDB?
3. What can you tell about advantages and disadvantages of NDBs? 4. Name the two main components of VOR.
5. How is the VOR accuracy increased?
6. What kind of information does DME give?
7. When does DME provide an extremely accurate position fix? 8. What is the function of ILS?
9. Name the two main units of ILS.
10. How many categories of ILSs can you name? How do they differ? 11. How many Omega transmitters exist?
12. Where are they situated?
13. Why has Global Positioning System got this name? 14. How many satellites make up the system?
15. What is GLONASS?
Vocabulary Practice