RADIO NAVIGATION AIDS - VOR/DME
Apart from taking their bearings (1) from the stars, how do pilots navigate? The answer, of course, is in the use of radio navigation aids. (2) There are a variety of different types of radio navigation aids but here we shall discuss VOR (3) and DME (4) only.
VOR and DME are often located at the same site. They operate on VHF and
UHF respectively and, as a consequence, are not affected by static (5) or other interferences. (6) The maximum range of VOR is about
200 nautical miles. (7) By
flying VOR the pilot ensures he is flying directly to the station. Also by
measuring his radials (8) from
more than one VOR station, a pilot can check his position.
The function of DME, which is short for Distance Measuring Equipment, is, as its title describes, to measure distance.
The DME measures, electronically, the time it takes for a signal, transmitted from an aircraft interrogator (9), to reach the ground base station transponder (10), and return.
This elapsed time is converted to miles and appears on a digital indicator on the flight deck. The indicator actually seems to rapidly count the number of miles between the aircraft and the station giving the pilot a continuous digital reading (11) of how far he is from, or to, a station.
With the many VOR/DME stations along his route, a pilot can make good his desired track; is constantly aware of his distance to or from a DME station; or, by using two VOR radials, establish his exact position.
VOCABULARY
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Bearing |
The angle between a direction and a reference direction as determined at the place of the observer. The reference direction is generally the North. |
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Radio navigational aids |
Also known as navaids. Electronic equipment for navigation. |
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VOR |
Very High Frequency Omni directional Range. |
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DME |
Distance Measuring Equipment. |
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Static |
In this case it is noise on the radio caused by atmospherics. |
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Interference |
Intrusion of another station making communication difficult or impossible. |
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Nautical miles |
A measurement of distance used primarily in navigation. It is equal to6080 feet or 1852 meters and is one minute of latitude at the equator. |
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Radials |
Airways or routes to and from a VOR station. |
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Interrogator |
Electronic equipment in the aircraft for navigation by DME. |
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Transponder |
A ground based receiver/transmitter which receives a radio signal from an aircraft and transmits it back to the aircraft. |
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In this case it is the figure or number (of miles) shown on the DME indicator on the aircraft instrument panel. |
CONVERSATION
By taking his position from the stars, a navigator can find his bearings.(1) Can a navigator find his bearings from the stars? Can a pilot find his bearings from the stars? Can you find your bearings from the stars? Who can find his bearings from the stars? Who can find his bearings from the use of navaids? (2) Does a map help you find your bearings when you are lost? Name different ways in which a pilot could find his bearings.
Is VOR (3) a navaid? Is VOR located on the ground? Is VOR also on the flight deck? Where is VOR? Does a pilot use VOR in order to navigate? Can he get his bearings with VOR? Why does I pilot use VOR
Is DME (4) a navaid? Is DME short for Distance Measuring Equipment? Can a pilot navigate with DME? Can he find his bearings with DME? Is DME a piece of electronic equipment? Is DME on very high frequency? UHF? In air traffic control? Where is DME? What does DME stand for?
Is static (5) a noise on the radio? Can you hear a radio programme if there is much static? Does static interfere (6) with the radio programme? Is static a pleasant noise? Do you like listening to static? Why don't you like listening to static? Does static interfere with VOR? DME? Why doesn't it interfere with VOR/DME? Can interference come from another station? Do you like listening to the radio with interference? Static? How do you like listening to the radio?
Are nautical miles (7) used in navigation? Do navigators measure distances in nautical miles? Do pilots measure distances in nautical miles? You? How do you measure distances? Pilots? Navigators?
Are radials (8) lines on a pilot's map? Do radials extend from VOR stations? Are radials on a road map? On what sort of map are radials? From where do radials extend?
Is an interrogator (9) a piece of electronic equipment? Is an interrogator on the flight deck? At an air traftic control centre? Where is an interrogator?
Is a transponder (10) also a piece of electronic equipment? On the ground? At a DME station? At a railway station? At what station is a transponder? What sort of equipment is a transponder?
The time by my watch is 0300 hours. What is the time by your watch? Is the reading (11) of your watch the same as mine? Is the reading of the pilot's altimeter the same as the air traffic controller's? What is the reading of this thermostat? Have you checked the reading on the thermostat? Can the pilot check the reading on his altimeter? Can the flight attendant check the reading on the altimeter? Who checks the reading on the altimeter?
WRITTEN EXERCISES
Instructions to students Answer the questions in your own words using full sentences. Write on a separate sheet of paper.
When a navigator uses a compass, the stars, VOR, a map, etc. what is he trying to find?
a.) Why does a pilot need both VOR and DME?
b.) What does the DME indicate to the pilot?
c.) In order to get a correct reading on his altimeter does a pilot check with air traffic control before he lands?
d.) What radio frequencies are VOR and DME operated on? And are they affected by static?
e.) Does an aircraft have to be fitted with instruments in order to receive radio signals?
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