Subscriber question:
"Sometimes when I fly an approach, the GPS seems to have a mind of its own and turns the airplane away from the path I expect, even when I think I have loaded the procedure correctly. How can I know where the box plans to take me?" — Kelly K.
Bruce:
“Detailed answers to those “What’s it doing now?” moments depend your GPS and autopilot, but one feature of your GPS can help you anticipate what the avionics are plotting—the flight plan page. Keep the flight plan page in view when you fly procedures, because it shows what the GPS will do, even when that’s not necessarily what you—or ATC—expect.
If you’re proceeding direct to a fix with a Garmin system, on the flight plan page a horizontal magenta arrow points to that waypoint. Preparing to intercept or track a leg between two waypoints? The arrow becomes a barbed magenta bracket that links the fixes. Those magenta markers sequence down the list of waypoints as you cross each fix, and they confirm the magenta line drawn on the map. Systems from other manufacturers display similar information, much like an FMS in a bizjet or airliner.
On the flight plan page, you can quickly make the box do what you (and ATC) want to happen next, such as proceed direct to a fix—even one behind you, as when being vectored off an approach; activate a leg to intercept when ATC assigns a heading; delete or skip over a hold or procedure turn; and so forth.
If you include an initial approach fix in your flight plan, the flight plan page will show a duplicate of that IAF when you load the approach. To avoid fumbling with the GPS as you begin an approach, always confirm that you have selected a fix or leg below the title of the procedure on the flight plan page. That step activates the approach and ensures that the GPS will sequence properly.
In newer systems, the flight plan page shows charted altitudes when you load an arrival or approach, and any vertical constraints that you create to ensure a smooth descent. Those altitudes are reminders to set the altitude bug as cleared by ATC, to select the correct autopilot-flight director modes, and to adjust power.
You can also customize the flight plan page to display other useful information, such as the cumulative distance to the runway when flying an approach. That’s helpful when complying with a tower’s instruction to report, say, a three-mile final, or when announcing your position at a non-towered airport.
Practice using the flight plan page—it’s not just for entering a route before you take off.”
Many GPS navigators allow you to load airways into your flight plan—but that’s not always the best choice. Here’s a video from our course Garmin GTN: Next Level that explains why.
How often does the autopilot start flying the aircraft in a direction you didn't expect?