A “NAV” warning flag will let you know that you should NOT trust the HSI indicator in the following cases:
- No waypoint is selected for the instrument;
- The waypoint distance is over 250 nautical miles;
- The GPS accuracy is bad;
- Ground speed is less than 5 Kts.
Note: Please note that you may still get correct deviation information when GPS accuracy is less than 2.5 nautical miles. In this case the compass card will be oriented to the north.