2015-08-21
1827
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.
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VOCABULARY
| 1. 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. |
| 2. Radio navigational aids | ─ Also known as navaids. Electronic equipment for navigation. |
| 3. VOR | ─ Very High Frequency Omni directional Range. |
| 4. DME | ─ Distance Measuring Equipment. |
| 5. Static | ─ In this case it is noise on the radio caused by atmospherics. |
| 6. Interference | ─ Intrusion of another station making communication difficult or impossible. |
| 7. 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. |
| 8. Radials | ─ Airways or routes to and from a VOR station. |
| 9. Interrogator | ─ Electronic equipment in the aircraft for navigation by DME. |
| 10. Transponder | ─ A ground based receiver/transmitter which receives a radio signal from an aircraft and transmits it back to the aircraft. |
| 11. Reading | ─ In this case it is the figure or number (of miles) shown on the DME indicator on the aircraft instrument panel. |
