CHAPTER 3. Navigation

Common Error: Forgetting To Re-Engage Sequencing Mode After Course Intercept

By far the most common error made with the nonsequencing mode is forgetting to re-engage the sequencing mode once the course has been intercepted. The result is that the FMS will not sequence to the next waypoint in the flight route upon reaching the active waypoint. The best indicator of this event is the “To/From” navigation display showing “From.” Normally all FMS fly “To” the waypoint, unless that unit does holding patterns. Flying “From” a waypoint can only be done in the “OBS”/“Hold”/“Suspend” mode.

Awareness: Remembering To Make Needed Mode Changes

The use of the sequencing and nonsequencing modes illustrates another aspect of maintaining good mode awareness—remembering to make required mode changes at future times during the flight. Remembering to do tasks planned for the future is a particularly error-prone process for human beings. Aviation’s first line of defense against such errors is the checklist. Creating your own checklist or callout procedures for maneuvers such as course intercepts is a good way to minimize this error. For example, a simple callout procedure for the course intercept maneuver might commence when the aircraft nears the point of interception. “Course is alive. Course is captured. Changing back to sequencing mode.”

Intercepting and Tracking a Course to a Different Waypoint

Figure 3-39 illustrates a slightly more complicated request often made by air traffic control. While en route to SUNOL, ATC instructs you to fly a heading of 060° to intercept and track the 049 course to TRACY. This situation requires two separate tasks: changing not only the inbound course, but also the active waypoint.

The first step is to change the active waypoint using the direct-to function, as illustrated in Figure 3-40. Remember, though, that if you use the direct-to function to make TRACY the active waypoint, the FMS calculates a desired track that takes you from the present position to TRACY intersection.

The second step, illustrated in Figure 3-40, is to change the desired track to TRACY by setting the computer in the nonsequencing mode and selecting the inbound course. You now continue on the assigned heading until the needle centers, then set the FMS back to the sequencing mode, and continue inbound on the assigned course to TRACY intersection.

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