Dynon’s Autopilot systems present two options for following a direction. Those two modes are HDG and TRK. Some pilots may be confused about the difference between these two autopilot control modes.
When HDG* or TRK modes are selected, the autopilot will follow the bug value selected by the pilot. This value is is indicated both by a digital value on the primary flight display and by the light blue bug icon located on the directional gyro. However, the actual flight path of the aircraft will vary depending on which mode is selected.
When HDG mode is engaged, the autopilot will place the aircraft’s magnetic heading on the value indicated by the bug and will maintain that heading until it is changed by the pilot. Magnetic heading is the direction that the aircraft is pointed.
In contrast, when the TRK mode is engaged, the autopilot will instead maneuver the aircraft so that it’s GPS ground track precisely follows the value indicated by the bug. To compensate for any crosswind, the autopilot will automatically guide the aircraft to the magnetic heading necessary to follow the GPS ground track indicated by the bug.
If one looks carefully at the directional gyro, a small magenta triangle will also be observed on the perimeter of the compass ring. This triangle points to the magnetic heading along which the aircraft’s current GPS ground track is aligned. With the autopilot engaged in TRK mode, one can observe that this magenta triangle will become nestled in the triangular notch in the light blue HDG/TRK bug as the ground track is properly aligned by the autopilot.
Practically speaking, if you want to fly in a certain direction over a map, say “North”, you should fly a TRK of 360. In this case, the autopilot knows what North is from the direction the aircraft is tracking over the ground from GPS, and it compensates for winds continuously. Similarly, using TRK mode to roughly intercept a desired location on SkyView’s map will work well, again, because the autopilot continuously corrects for winds.
In contrast, HDG is most useful for pilots that are navigating under air traffic control. ATC assumes that pilots only have access to what direction the nose of the aircraft is pointed. This is magnetic heading. And so because of that, ATC requires that pilots report mag heading, not track, when navigating under their control. ATC then applies wind correction to each aircraft equally, and because ATC has everyone on radar, everyone remains separated and gets where they want to go. The disadvantage of HDG mode when used without ATC guidance is that wind can blow you considerably away from the direction that you were aiming.
Special Note:
When HDG* or TRK modes are selected, the autopilot will follow the bug value selected by the pilot. This value is is indicated both by a digital value on the primary flight display and by the light blue bug icon located on the directional gyro. However, the actual flight path of the aircraft will vary depending on which mode is selected.
In the SkyView system, the bug on the directional gyro is most commonly referred to as the “heading” bug, and its value on the primary flight display will be labeled HDG. This digital HDG bug value is located at approximately the 7 O’clock position of the directional gyro.
The pilot-selectable function associated with this bug value for the two knobs on the SkyView display is likewise labeled HDG, except when the autopilot is engaged in the TRK mode. In that case, the knob function label is automatically changed to TRK to remind the pilot of the autopilot’s response to changes by that control, as is the digital indication of the bug’s value on the PFD. When the autopilot is disengaged or a different autopilot mode is selected, that knob function will revert to the default value of HDG.
*In the SkyView system, HDG mode is only available as an autopilot mode when the Autopilot Expert Control Scheme is selected by the pilot. Kirk Kleinholz, CFII, Sales Manager Michael Schofield, Marketing Manager
The pilot-selectable function associated with this bug value for the two knobs on the SkyView display is likewise labeled HDG, except when the autopilot is engaged in the TRK mode. In that case, the knob function label is automatically changed to TRK to remind the pilot of the autopilot’s response to changes by that control, as is the digital indication of the bug’s value on the PFD. When the autopilot is disengaged or a different autopilot mode is selected, that knob function will revert to the default value of HDG.
*In the SkyView system, HDG mode is only available as an autopilot mode when the Autopilot Expert Control Scheme is selected by the pilot. Kirk Kleinholz, CFII, Sales Manager Michael Schofield, Marketing Manager