CHAPTER 3. Navigation

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 unitís features. Always check for correct navigation source selection and cross-check against the published procedure. Be ready and able to fly and navigate manually.

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