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