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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. 

## VOR/DME RNAV Components 

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. 

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Most VOR/DME RNAV systems have the following airborne controls: 

1. OFF/ON/Volume control to select the frequency of the VOR/DME station to be used. 

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. 

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. 

## Function of VOR/DME RNAV 

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 

