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 unit’s memory is very limited, the pilot should also be adept at removing the waypoint.
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.
Risk: What Lies Ahead on a Direct-To Route?
The direct-to function offers a convenient way to shorten your time and distance en route if ATC authorizes that track. When you perform a direct-to operation, though, remember that the system builds a new track from your present position to the new waypoint. This track does not necessarily correspond to any previously planned airway or route, so it is critical to ensure that your new direct route is clear of all significant obstructions, terrain, weather, and airspace.
Cancel Direct To
ATC may sometimes cancel a previously issued direct-to clearance and ask you to resume the previously cleared route. Most FMSs offer a simple way of canceling a direct-to operation. Figure 3-24 illustrates the procedure for one FMS.
Selecting a Different Instrument Procedure or Transition
ATC will sometimes issue an instrument procedure or transition that is different from what you would expect. Entering a new procedure or transition is usually a simple matter of making new menu choices, as illustrated in Figure 3-25. In most units, if you are training or wish to fly the approach again, you must learn how to set the selector or cursor back to the initial fix, which will restart the approach sequence.
Proceeding Directly to the Nearest Airport
One of the most useful features of an FMS is its ability to provide you with immediate access to a large navigation database. This feature is particularly useful when a suitable nearby airport or navigation facility must be located quickly. Figure 3-26 shows how to locate and proceed directly to the nearest suitable airport using one manufacturer’s system.
- Proceed directly to a waypoint in the programmed route.
- Cancel a programmed or selected waypoint or fix.
- Select a different instrument procedure or transition.
- Restart an approach sequence.
- Immediately find the nearest airport or facility.
- Edit a flight plan.
- Enter a user waypoint.