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2. Nonsequencing mode stops the waypoint sequencing feature of the FMS/RNAV unit. If engaged in nonsequencing mode, the FMS/RNAV program does not automatically sequence to the next waypoint in the flight plan when the aircraft arrives at the active waypoint. 

Every FMS/RNAV offers a way to switch to the nonsequencing mode. There is typically a button marked OBS (or Hold), and an OBS or course selection knob to select an inbound course to the active waypoint. Figure 3‑38 illustrates the procedure for one particular FMS. 

Once you switch to nonsequencing mode and select the inbound course of 009°, the navigation indicator reflects aircraft position with respect to the 009° course. The navigation indicator in Figure 3-38 shows that you are west of course. The assigned heading of 080° provides an acceptable intercept angle. As you fly the 080° heading, the needle centers as you reach the 009° course. Once the 009° course is reached and the needle has centered, you can turn to track the 009° course inbound to SUNOL. 

It is important to remember that the nonsequencing mode suspends the FMS/RNAV’s waypoint sequencing function. If you reach SUNOL and the unit is still set in the nonsequencing mode, it will not sequence on to the next waypoint. Generally, once established on a direct course to waypoint or navaid, switching back to sequencing (releasing the Hold or Suspend function) mode allows the FMS/RNAV to continue to the programmed point and thence onward according to the programmed routing. Setting the computer back to the sequencing mode is usually accomplished by pressing the OBS (Hold or Suspend) button again. 

## 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. 

