CHAPTER 3. Navigation

En Route Modifications

Part of the challenge of using FMS en route is dealing with modifications to the planned flight route. This section describes five en route modifications.

Adding and Deleting Waypoints From the Programmed Route

All FMS/RNAV units allow en route (not published departure, arrival or approach) waypoints to be added and deleted to the programmed route. These techniques are illustrated in Figure 3-22.

ATC may issue instructions to a point defined by a VOR radial and DME value. The pilot must know how to enter such a waypoint as a user waypoint, name it, and recall it. If the unitís memory is very limited, the pilot should also be adept at removing the waypoint.

Direct To

Another simple modification is one that requires the pilot to proceed directly to a waypoint. In some cases, the waypoint to fly directly toward is one that already appears in the programmed flight plan. In this case, the pilot simply selects that waypoint in the flight plan and activates the direct-to function, as illustrated in Figure 3-23.

The direct-to waypoint now becomes the active waypoint. After reaching this waypoint, the system proceeds to the next waypoint in the programmed route.

In other cases, you may be asked to fly directly to a waypoint that does not already appear in the programmed flight route. In this case, one strategy is to add the waypoint to the programmed route using the technique illustrated in Figure 3-22, and then proceed directly to the waypoint using the technique illustrated in Figure 3-23. Another option is to use the direct-to function to get the flight started toward the assigned waypoint, and then add the new waypoint to the appropriate place in the programmed flight plan.

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