We have upgraded the Garmin 430 to WAAS in our homebuilt. We have the
Garmin talking to our STEC autopilot using its ARINC 429 roll steering
commands through the STEC GPSS interface. In the old 430 non-WAAS
unit, even if you selected an ILS approach on the Garmin and loaded
it, you would get roll steering commands down to the ground out of the
Garmin. Of course, you are using the VLOC receiver and the ground
stations for the approach but the autopilot would still fly the
magenta line on the screen that was provided "for guidance". I now
notice on the WAAS'd unit we got back that the roll steering commands
only seem to be provided until we get to the ILS final approach fix,
and then the STEC starts flashing to indicate that there is no more
roll steering. It drops out at the FAF.
We have to revert to HEADING mode if we still want to use the
autopilot on the approach or maybe NAV mode and track the localizer
needle, although I cut those wires figuring that roll steering is so
good I would never again want to track needles.
If we are flying a GPS or an RNAV approach on the 430W it does give
the roll steering signals all the way down to the ground or out to the
holding fix on the missed approach and will even fly the holding
pattern.
Anyone else can confirm this? I called Garmin technical support and
the guy really couldn't get what I was talking about. He was under
the impression that we should not be getting ANY roll steering on an
ILS approach but that was not the case with the 430 and semi-not the
case with the 430W.
Is this a deliberate feature programmed into the software to insure
that you are not flying the "guidance only" course line on an ILS
approach?