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When combined, use of the FMS and the FD/autopilot’s navigation function result in an automated form of flight that was formerly limited to very complex and expensive aircraft. This same level of avionics can now be found in single‑engine training airplanes. While it is easy to be complacent and let down your guard, you must continuously monitor and stay aware of automated systems status and function and the track of the aircraft in relation to the flight plan and air traffic control (ATC) clearance. 

## GPS Steering (GPSS) Function 

Many autopilots offer a global positioning system steering (GPSS) function. GPSS does all of the same actions as the navigation function, but achieves a higher degree of precision by accepting inputs directly from the GPS receiver. Consequently, the GPSS function follows the desired track to the active waypoint more aggressively, permitting only small excursions from the desired course. On some installations, pressing the autopilot NAV button twice engages the GPSS function. 

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## Following a VOR Radial 

The FD/autopilot’s navigation function can also be used to directly track VOR radials. The navigation display must be configured to show indications from one of the aircraft’s VOR receivers. Once you have tuned and identified a VOR station and selected the desired radial, you can select the navigation mode to track the selected radial. Figure 4-7  demonstrates how to use the navigation mode to follow a VOR radial. 

When the navigation mode is used to follow a route defined by VOR radials, you must still tune and identify each new VOR facility manually and select the appropriate radials along the way. The autopilot’s navigation function cannot automatically manipulate the VOR receiver. However, some highly automated FMS units tune and identify VORs along a defined route, such as Victor or Jet routes. You should check the FMS documentation and installed options. 

