CHAPTER 3. Navigation

Waypoint Alerting

The first service performed by the sequencing mode is waypoint alerting. Just prior to reaching each active waypoint, waypoint alerting advises the pilot of imminent arrival at the active waypoint. Waypoint alerting is illustrated in Figure 3-18.

Turn Anticipation

The second service performed by the sequencing mode is turn anticipation. During waypoint alerting and prior to reaching the active waypoint, the FMS indicates that it is time to begin the turn to fly the desired track to the new active waypoint. The timing of turn anticipation is based on the aircraft’s observed groundspeed and the angle of the turn required to track to the next waypoint. If a standard rate turn is begun when the waypoint alerting indication is presented, the pilot should roll out on course when the aircraft reaches the center of the desired track to the new active waypoint. Turn anticipation is also illustrated in Figure 3-18.

When turn anticipation is used, the aircraft does not fly directly over the active waypoint. Rather, the computer commands a turn that “rounds the corner” to some degree, giving priority to having the aircraft roll out on the new desired track to the new active waypoint. This function is illustrated in the upper illustration in Figure 3-19.

Turn anticipation occurs only when the active waypoint is designated as a fly-by waypoint. A fly-by waypoint is one for which the computer uses a less stringent standard for determining when the aircraft has reached it. By contrast, some waypoints are designated as flyover waypoints. The FMS will not use turn anticipation for a fly-over waypoint; instead, the navigation will lead the aircraft directly over the waypoint (hence the name). A missed approach waypoint is a typical example of a fly-over waypoint. A fly-over waypoint is illustrated in Figure 3-19.

Waypoint Sequencing

The third service performed by sequencing mode is waypoint sequencing. Once the aircraft reaches the active waypoint, the FMS automatically makes the next waypoint in the flight plan sequence the new active waypoint. Waypoint sequencing is illustrated in Figure 3-20.

Awareness: Making Waypoint Callouts

To help you stay in touch with the progress of the flight while the FMS automatically performs the navigation task, it is a good practice to announce your arrival (mentally, single pilot; or orally, to the flight crew) at each waypoint in the programmed route. For example, when arriving at SUNOL intersection, you might announce, “Arriving at SUNOL.

TRACY is next. The course is 051 degrees, and the ETE is 10 minutes.”

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