Trutrak Vertical IAS

Just started flying and am checking ap functions and am having difficulty getting ap to descend correctly, then I noticed this from manual:

In ALT – Indicated airspeed mode the autopilot will make the aircrafts altitude follow the Teal colored altitude bug. When you change the altitude bug the autopilot will climb or descend following the Yellow Airspeed Bug. You can change the Airspeed Bug using the SET > IAS center EFIS knob. IAS mode only works with the Dynon AP servos.


Since I have trutrak servos is this correct for ias mode? If so what shoud I expect-no control, erratic control, searching? Mode not usable with tt servos or is there a software fix?

I’m also having trouble getting the ap to descend in vs mode. For example going from fix to fix the ifd540 prompts “begin to descend in x seconds”. Flying at 4000 vs bug set to 3000 but get no descent. What should I be looking for for correct operation?

If I remember correctly, there is a blurb in the V15 manuals that states the IAS bug only works with the Dynon AP.

To get the AP to descend you to be in the VNAV ARM mode. You use the altitude bug to adjust the altitude until you intercept the glideslope, then the AP will engage and follow the glideslope

By default when controlling a Trutrak autopilot the EFIS will descend in VS mode when IAS is selected.

The IAS mode was added to control the integrated autopilot servos. These servos are the only ones we can control fast enough to control decent with IAS.