If the system is unable to find the aircraft heading, but GPS-based track information is available, the HSI displays the ground track instead of heading using HSI Track Mode. In this mode, a white ‘TRK’ annunciation and track display appear on the HSI.

When in track mode, the diamond representing the current GPS track replaces the black triangle (lubber line) representing the current heading, and the magenta diamond representing GPS track remains fixed near the top of the HSI.