Navigation

would show approximately 1.0 NM on the DME.) DME is a While the capabilities and methods of operation of VOR/ very useful adjunct to VOR navigation. A VOR radial alone DME RNAV units differ, there are basic principles of merely gives line of position information. With DME, a pilot operation that are common to all. Pilots are urged to study may precisely locate the aircraft on a given line (radial). the manufacturer’s operating guide and receive instruction prior to the use of VOR/DME RNAV or any unfamiliar Most DME receivers also provide GS and time-to-station navigational system. Operational information and limitations modes of operation. The GS is displayed in knots (NMPH). should also be sought from placards and the supplement The time-to-station mode displays the minutes remaining to section of the AFM/POH. VORTAC station passage, predicated upon the present GS. GS and time-to-station information is only accurate when VOR/DME-based RNAV units operate in at least three tracking directly to or from a VORTAC. DME receivers modes: VOR, en route, and approach. A fourth mode, VOR typically need a minute or two of stabilized flight directly Parallel, may also be found on some models. The units need to or from a VORTAC before displaying accurate GS or both VOR and DME signals to operate in any RNAV mode. time-to-station information. If the NAVAID selected is a VOR without DME, RNAV mode will not function. Some DME installations have a hold feature that permits a DME signal to be retained from one VORTAC while the In the VOR (or non-RNAV) mode, the unit simply functions course indicator displays course deviation information from as a VOR receiver with DME capability. [Figure 16-36] The an ILS or another VORTAC. unit’s display on the VOR indicator is conventional in all respects. For operation on established airways or any other VOR/DME RNAV ordinary VOR navigation, the VOR mode is used. Area navigation (RNAV) permits electronic course guidance on any direct route between points established by the pilot. To utilize the unit’s RNAV capability, the pilot selects and While RNAV is a generic term that applies to a variety establishes a waypoint or a series of waypoints to define a of NAVAIDS, such as GPS and others, this section deals course. A VORTAC (or VOR/DME) needs to be selected with VOR/DME-based RNAV. VOR/DME RNAV is not a as a NAVAID, since both radial and distance signals are separate ground-based NAVAID, but a method of navigation available from these stations. To establish a waypoint, a using VOR/DME and VORTAC signals specially processed point somewhere within the service range of a VORTAC is by the aircraft’s RNAV computer. [Figure 16-35] defined on the basis of radial and distance. Once the waypoint is entered into the unit and the RNAV en route mode is NOTE: In this section, the term “VORTAC” also includes selected, the CDI displays course guidance to the waypoint, VOR/DME NAVAIDs. not the original VORTAC. DME also displays distance to the waypoint. Many units have the capability to store several In its simplest form, VOR/DME RNAV allows the pilot to waypoints, allowing them to be programmed prior to flight, electronically move VORTACs around to more convenient if desired, and called up in flight. locations. Once electronically relocated, they are referred to as waypoints. These waypoints are described as a RNAV waypoints are entered into the unit in magnetic combination of a selected radial and distance within the bearings (radials) of degrees and tenths (i.e., 275.5°) and service volume of the VORTAC to be used. These waypoints distances in NM and tenths (i.e., 25.2 NM). When plotting allow a straight course to be flown between almost any RNAV waypoints on an aeronautical chart, pilots find it origin and destination, without regard to the orientation of VORTACs or the existence of airways. OFFSET EN ROUTE 3 3 R BEARING LOAD DISTANCE N A V 4 4 3 3 4 2 7 9 8 8 12 12 Area Navigation Direct Route Figure 16-36. RNAV controls. Figure 16-35. Flying an RNAV course. 16-28