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Area Navigation (RNAV) Basics: RNAV Concept

by Flight Learnings

in Navigation

Area Navigation (RNAV) is a navigation technique that allows pilots to navigate directly between any two points on the globe. Using RNAV, any location on the map can be defined in terms of latitude and longitude and characterized as a waypoint. Onboard RNAV equipment can determine the present position of the aircraft. Using this positional information, the equipment can calculate the bearing and distance to or from any waypoint and permit navigation directly between any two waypoints. In this way, RNAV overcomes a fundamental limitation of conventional navaid point-to-point navigation techniques, which require navigating between electronic navigation transmitters on the ground. The following examples illustrate this limitation.

An aircraft equipped with conventional VOR receivers is positioned at Point A as shown in the diagram at the top of Figure 3-1, and the pilot wishes to navigate directly to Point B. Although there appear to be a few VOR stations in the vicinity of the aircraft, it is not clear whether reception is possible from the aircraft’s present position. If the VOR stations are within reception range, the pilot has two choices: (1) fly to intercept the closest airway, then track it to the intersection; or (2) fly to intercept an extension of the radial that defines Point B (assuming reception is possible). Neither alternative provides the pilot with a means of flying directly to the intersection.

Figure 3-1. Limitations of conventional navigation.

Figure 3-1. Limitations of conventional navigation.

Suppose the same aircraft is positioned at Point A as shown at the bottom of Figure 3-1 and the pilot wishes to navigate directly to Point C, which is neither a VOR station nor airway intersection. This pilot has an even more difficult situation.  Assuming the VOR stations are within reception range, the pilot needs to create two makeshift airways using a navigation plotter and chart, fly to intercept one of them, then track to Point C (which the pilot has defined as the intersection between the two courses). Flying a direct course to Point C with any degree of accuracy is not possible. Since RNAV systems are not bound by these limitations, the entire airspace is available for navigational use. The national airspace system can thus accommodate more aircraft. However, when the pilot leaves the established airways, he or she also leaves the guaranteed obstruction clearances designed into the airway system. Always plan flights above the maximum elevation figure (MEF) displayed on sectional charts when flying off airways, and be aware that man-made obstructions such as towers may not be added to charts for some time after construction. If flying a new routing, allow for construction, which may not be published yet.

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