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was selected in the FMS. Every advanced cockpit offers buttons or switches that allow you to choose which navigation indications will be shown on which display or instrument. 

This situation becomes complicated in aircraft that contain dual FMS/RNAV installations and redundant selectable displays or instruments. The pilot must learn how to configure each navigation instrument to show indications from each possible navigation source. 

Figure 3-16  shows an example of a primary flight display (PFD) navigation indicator that combines a course deviation indicator (CDI) and a radio magnetic indicator (RMI), and allows the pilot to display indications from one of two FMS on either indicator. 

## Common Error: Displaying the Wrong Navigation Source 

The annunciations showing which navigation sources are displayed on which navigation instruments are often small, so there is significant potential for displaying a navigation source other than the one you intended to select. The consequences of losing track of which navigation signals you are following 

can be significant: you may think you are steering along one course when in fact you are steering along a different one. Be sure to verify these settings prior to departure, and again each time you make changes to any navigation instrument. Some installations compound this potential with automatic source switching. The most common switching mode is a GPS source to be automatically deselected when the VOR is set to an ILS localizer frequency and a signal is present. Typically, that is not a problem since the pilot intends to switch to the ILS anyway. However, the error arises upon missed approach, when the pilot selects another frequency to follow a VOR missed approach routing. At that point, some units revert back to the previous GPS or other RNAV routing selected instead of the VOR frequency that the pilot just picked. This can result in gross navigation errors and loss of obstruction clearances. In some units, this is a shop programmable or jumper selected option. Check your unit’s features. Always check for correct navigation source selection and cross‑check against the published procedure. Be ready and able to fly and navigate manually. 

