248 °  308 °  0  1 0  $_{2}$$_{0}$ 3 0 4 0 5 0 6 0 7 0 A N G L E 3 A N G L E 1 A N G L E 2 VOR/DME  C  A  B  Waypoint  Figure 7-19. Figure 9-22. RNAV computation. angles 1 and 2 and determines angle 3 and side C, which is  the distance in NMs and magnetic course from the aircraft  to the WP. This is presented as guidance information on the  flight deck display. Although RNAV flight deck instrument displays vary among  manufacturers, most are connected to the aircraft CDI with a  switch or knob to select VOR or RNAV guidance. There is  usually a light or indicator to inform the pilot whether VOR  or RNAV is selected.  [Figure 9-23]  The display includes the  WP, frequency, mode in use, WP radial and distance, DME  distance, groundspeed, and time to station. While DME groundspeed readout is accurate only when  tracking directly to or from the station in VOR/DME mode,  in RNAV mode the DME groundspeed readout is accurate  on any track. The advantages of the VOR/DME RNAV system stem from  the ability of the airborne computer to locate a WP wherever it  is convenient, as long as the aircraft is within reception range  of both nearby VOR and DME facilities. A series of these  WPs make up an RNAV route. In addition to the published  routes, a random RNAV route may be flown under IFR if  it is approved by air traffic control (ATC). RNAV DPs and  standard terminal arrival routes (STARs) are contained in  the DP and STAR booklets. VOR/DME RNAV approach procedure charts are also  available. Note in the VOR/DME RNAV chart excerpt shown  in  Figure 9-24  that the WP identification boxes contain the  following information: WP name, coordinates, frequency,  identifier, radial distance (facility to WP), and reference facility  elevation. The initial approach fix (IAF), final approach fix  (FAF), and missed approach point (MAP) are labeled. To fly a route or to execute an approach under IFR, the RNAV  equipment installed in the aircraft must be approved for the  appropriate IFR operations. In vertical navigation (VNAV) mode, vertical guidance is  provided, as well as horizontal guidance in some installations.  A WP is selected at a point where the descent begins,  and another WP is selected where the descent ends. The  Figure 9-23. Onboard RNAV receivers have changed significantly.  Originally, RNAV receivers typically computed combined data  from VOR, VORTAC, and/or DME. That is generally not the case  now. Today, GPS such as the GNC 300 and the Bendix King KLS  88 LORAN receivers compute waypoints based upon embedded  databases and aircraft positional information. Function of VOR/DME RNAV VOR/DME RNAV Components 2.  MODE select switch used to select VOR/DME  mode, with: a. Angular course width deviation (standard VOR  operation); or b. Linear cross-track deviation as standard (±5 NM  full scale CDI). 3.  RNAV mode, with direct to WP with linear cross-track  deviation of ±5 NM. 4.  RNAV/APPR (approach mode) with linear deviation  of ±1.25 NM as full scale CDI deflection. 5.  WP select control. Some units allow the storage of more  than one WP; this control allows selection of any WP  in storage. 6.  Data input controls. These controls allow user input  of WP number or ident, VOR or LOC frequency, WP  radial and distance. 1.  OFF/ON/Volume control to select the frequency of the  VOR/DME station to be used. 9-23 Most VOR/DME RNAV systems have the following  airborne controls: