13. Radio navigation aids – vor; dme.

Navigation us the directing of aircraft from one place to another along a particular line of travel. To navigate a pilot uses radio navigation aids. There are a variety of different types of radio navigation aids.

VOR (omnidirectional radio range) and DME (distance measuring equipment) are often located at the same site. They operate on VHF and UHF respectively and are not affected by static or other interferences. The maximum range of VOR is about 200 nautical miles. By flying VOR the pilot ensures he is flying directly to the station. Also by measuring radials from more than one VOR station, a pilot can check his position.

The function of DME is to measure distance. The DME measures, electronically, the time it takes for a signal, transmitted from an aircraft interrogator, to reach the ground base station transponder, 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 of how far he is from or to station.

With the many VOR/DME stations along the route, a pilot can make good his desired track; is constantly aware of his distance to or from DME station; or, by using two VOR radars, establish his exact position.

Non-Directional Beacon (NDB).

This most basic of all aids is still used in less developed areas to mark air routes, its useful range being up to as a Locator Beacon, with a range of about 15 miles in this application. The NDB consist of a radio transmitter in the medium frequency band which sends out a continuous steady signal in all directions. A callsign of two or three letters in Morse code is superimposed at regular intervals as a check that the desired beacon has been selected.