15

Area Navigation (RNAV)

Area navigation (RNAV) allows you to fly point to point on a direct course without having to overfly ground-based NAVAIDs. Instead of flying from VORTAC to VORTAC along Victor airways on what might be a circuitous route, you can fly direct from your departure airport to the destination airport, or from waypoint to waypoint, using RNAV. A waypoint is a predetermined geographical position usually specified by latitude and longitude, or by radial and distance from a VORTAC, and used to define an RNAV route or instrument approach.

Some RNAV systems can define a waypoint internally by the pilot inserting latitude and longitude into the computer, and then deriving data from navigation systems such as GPS; other RNAV systems define waypoints relative to a VORTAC, using radial and distance (or latitude and longitude) to create “phantom” VORTACs, known as pseudo-VORTACs.

Know what navigation system you are following on the CDI!

Many RNAV units also serve as the regular Nav 1 VOR receiver and share a common CDI display. Some devices include a button for the pilot to select RNAV or VOR. Many pilots have followed VOR information when they thought they were using RNAV or vice versa.

RNAV Using Pseudo-VORTACs

Many general aviation aircraft have a course line computer system which, when used in conjunction with the NAV/COM radio selected to a VORTAC, can electronically relocate that VORTAC, so that a pseudo-VORTAC (an offset VORTAC) is created at any desired waypoint. It does this by electronically adding a vector (radial and distance) to the position of the actual VORTAC.

You can locate pseudo-VORTACs wherever you like, provided they are within signal reception range of the parent VORTAC, and thereby create a series of waypoints along your desired route.

The normal NAV/COM receiver is selected to the parent VORTAC, and the RNAV computer is programmed to electronically add the vector (radial and distance) to receive VORTAC signals. How this is done depends on the actual equipment in the cockpit — refer to equipment information in your Pilot Operating Handbook.

The course deviation indicator (CDI) receives its input via the computer, and indicates deviation from course between the waypoints — not an angular deviation as for normal VOR flying, but a lateral deviation in nautical miles, or fractions thereof. A one-dot deviation of the CDI might be 1 NM off course during the en route phase; in the approach mode, a one-dot deviation might be 0.25 NM off course. Many RNAV units have a “mode” button that gives the pilot the choice of lateral or angular deviation.

The course between waypoints is maintained by keeping the CDI centered. Because it indicates lateral deviation in nautical miles, known as crosstrack deviation, rather than angular deviation, there is no “funneling” effect using the RNAV CDI. (Normal VOR tracking is 2° deviation per dot; normal localizer tracking is 0.5° per dot.) Distance to the waypoint is shown on the normal DME indicator.

The waypoints can normally be preset on the RNAV equipment, and then instantaneously recalled as you need them. As the flight progresses, you will proceed through the waypoints in order, keeping within signal range of each parent VORTAC by flying at a suitable altitude and distance from it. If the usable signal range is exceeded, the CDI OFF flag will show.

Typical RNAV systems can provide:

• crosstrack deviation from the selected course in nautical miles with TO/FROM information;
• distance to the waypoint in nautical miles;
• groundspeed in knots;
• time-to-waypoint in minutes.

RNAV Approach

An approved RNAV receiver is required for you to fly an RNAV approach, which is a nonprecision approach, and is flown like a VOR/DME approach, down to a minimum descent altitude (MDA).

Each RNAV approach must have at least two waypoints, but there are generally more. These waypoints should be preset, and then recalled as you need them. The RNAV waypoints are defined on the charts by both:

• latitude and longitude (expressed in order of keypad insertion); and
• radial and distance from the parent VORTAC.

The missed approach point (MAP) on an RNAV approach is indicated when the TO flag changes to FROM, at which point you must commence the missed approach procedure if you do not have the runway environment in view.

Some RNAV systems provide a vertical navigation (VNAV) capability — in other words, three-dimensional area navigation. It may be used en route, or it may be used in the approach phase to provide a particular flight path angle (FPA) to the runway, shown on the chart under the final approach path. In VNAV mode, a waypoint (WP) is selected at a point where the descent begins, and another WP selected where the descent ends. The RNAV equipment computes the rate of descent relative to the groundspeed; on some installations, it displays vertical guidance information on the GS indicator. When using this type of equipment during an instrument approach, the pilot must keep in mind that the vertical guidance information provided is not part of the nonprecision approach. Published nonprecision approach altitudes must be observed and complied with, unless otherwise directed by ATC.

RNAV Routes and Procedures

Aircraft equipped with approved area navigation systems are permitted to operate on designated RNAV routes. The coordinates for each leg of the flight plan are entered into the RNAV computer prior to departure. This can be accomplished manually or, in the case of more advanced systems, by a database unit which has stored positions and routes and which interfaces with the RNAV system navigation computer.

Note. Regardless of the source of waypoint coordinates, it is important that all tracks and distances generated by the RNAV computer are checked for accuracy against the published and flight planned tracks and distances for the route concerned.

RNAV Data Displayed

Typical information on RNAV system CDUs includes:

• present position of the aircraft in latitude–longitude coordinates;
• crosstrack deviation from the selected course in nautical miles;
• distance to the next waypoint in nautical miles;
• groundspeed in knots;
• time to the next or subsequent waypoints in minutes; and
• with a TAS input, current wind velocity.

Review 15

Area Navigation (RNAV)

1. What is a pseudo-VORTAC?

2. How is a pseudo-VORTAC created?

3. What does the CDI display when it is used as part of an RNAV system?

4. Which units are used for indications on the RNAV CDI?

5. What are fixes along an off-airways route known as?

6. What is a predetermined geographical position used for an RNAV route or an RNAV instrument approach known as?

7. How would you identify the Final Approach Fix?

8. How can you determine if your GPS equipped airplane is approved for IFR operations?

9. Refer to figure 15-5.

a. On which NAVAID is this approach based?

b. How many waypoints must you insert?

c. What is the more appropriate IAF?

d. What should you do to reverse direction at HOPES for the inbound final approach?

e. What is the final approach course (MC)?

f. What is the distance from HOPES to the runway threshold (NM)?

g. Passing HOPES, to what altitude can you descend?

h. What are the minimums for a straight-in landing?

i. What are the minimums for a circling approach to Rwy 35?

j. At what point are you able to descend to the MDA?

k. Where is the MAP?

l. How is passing the MAP indicated?

m. Where should you hold following a missed approach?

n. What is the touchdown zone elevation (TDZE) for Rwy 17?

10. Can you descend down to the minimum descent altitude after crossing the final approach fix?