From HXr manual - 12.3.5.1.1 Capturing the ILS with ARM

[BillinDurham]

Having done a number of ILS intercepts with the ARM feature engaged, I’ve never managed to have the system automatically switch from HDG mode to NAV mode, when ARM is engaged, as it intercepts the Localizer. Instead I’ve had to manually switch from HDG to NAV in order to have the AP do the intercept. Otherwise my AP blows right through the Localizer. It just happened again yesterday when I had a good chance to observe this situation on an actual VTF ILS approach.

Any thoughts on why that may be?

My only thought involves the EXECUTE key. I recall that originally that did not exist but it was added for some reason (?). I believe I did what was needed to enable the EXECUTE key and have used it once cleared for an approach. But over time it has become unclear exactly what it does. Originally it was not needed since ARMing an approach was enough. I’m thinking that use of the EXECUTE key may in some way interfere with the automatic switch from HDG to NAV mode when on VTF.

My config includes and HXr, a couple of HXs, an Avidyne IFD440 and a TruTrak Digiflight II AP.

Thanks in advance

[GRT_Jeff]

The EXECUTE key was added as suggested by people flying IFR approaches so they could set up the approach before final and only have to push one button to allow the final approach capture.

When one of the approach modes is armed, the EFIS will not change modes and capture the indicators until EXECUTE is pushed. EXECUTE is to be pushed after all turns are complete, as the EFIS only knows how to fly a straight in final approach. In the 12.3.5.1.1 diagram the EXECUTE button would be between steps 1 and 2.

After you push EXECUTE, the EFIS starts looking at the localizer deviation signal. When it's within 2 dots left or right for several seconds it will capture the signal and that includes switching to ENAV mode.