Navigation source and preview

The primary navigation source and a preview source can be shown together. FSS describes FMS deviation as a magenta diamond. The localizer pointer is a trapezoid: cyan in preview and green when the localizer is the primary source. A preview is not proof that the localizer is active. If both lateral pointers coincide, the FMS pointer covers the localizer pointer.

Identify the primary source

Read the navigation-source indication and the lateral FMA.

Identify the preview

If preview is selected, check the receiver, frequency and course against the chart.

Arm the approach

Use the documented approach setup and confirm the armed mode. For an ILS with FMS source, FSS says pressing APP without a NAV1 or NAV2 preview has no effect.

Watch the change

As the localizer becomes usable, verify the source and FMA transition described for your build.

Check actual tracking

Compare deviation, heading, ground track and aircraft response. A centred preview alone is not proof of active LOC tracking. ^[200]