We have a newly purchased Lance with G530WAAS and Altimatic IIIC autopilot. I have read the POH, but have not yet had the opportunity to read a manual for the AP. Does anyone have experience with this AP? It followed the heading well for a local LPV approach, but did not follow the glideslope. I appologize for not studying more, but does anyone have an easy answer for how to convince it to follow the glideslope?
In order to follow an LPV approach glideslope the IIIC would have to "think" it was "seeing" a localizer, e.g. it would have to be in Loc on the heading select. Don't think it will do it. I have a IIIc in the 'kota and the only time it's fully coupled is on a traditional ILS. Now maybe I'm not setting it up right but have never tried localizer mode when gpss. I do know that if it isn't in localizer mode then it won't track a glideslope - the computer just can't do it (as I understand it).
Why don't you start by reading the manual on this autopilot? http://www.centuryflight.com/images/operating-manuals/CENTIII.pdf Note that the Altimatic IIIC is essentially a Century III with a different nameplate. In any event, Clark is correct -- this autopilot will not engage the glide slope unless it is in LOC or LOC BC mode, with altitude hold engaged at least some number of seconds (see the book) before intercept, and intercepting the GS from below. How you get to that point will depend in part on whether or not you have a GPSS roll steering adapter installed.
The Century/Autocontro-III radio coupler has 5 modes: NAV, OMNI, HDG, LOC NORM, and LOC REV (commonly called BC) and only the LOC NORM mode allows GS capture and tracking. And the autopilot has to be in ALT mode and the radio coupler has to be in LOC NORM mode for approximately 20 seconds with a 30-60% "fly up" indication although the exact time required depends on the GS indication (less deflection requires more time). The 20 seconds in the manual assumes the airplane is in level flight (pretty much a given if ALT mode is working). Also FWIW, the lateral position of the aircraft relative to the LOC centerline has no effect on GS coupling. IOW some (or all) of those 20 seconds can be when the airplane hasn't intercepted the LOC yet.
I saw an interesting post on another site which was confirmed by my avionics shop that it is indeed possible to fly GPS precision approaches coupled with the III Altimatic C: ----- This is a common problem. The most likely reason is the installer did not hook up the correct signal to the autopilot. In the olden days, when an ILS receiver was hooked to an autopilot such as the CIII, the ILS receiver generated a signal called "ILS Energize" and its purpose was to tell the autopilot that a GS could be expected on this frequency. It still exists on the GNS430W, but this signal is not used in the installation manual. Instead another signal called "ILS/GPS Approach" is used for the same purpose and is also active when ever there is a GPS approach selected. It is the one that should be used, Unfortunately, not all avionics technicians look at the install manual interconnect, so they go from memory what they have done in the days before GPS. The pin they should use on the GNS430W is P4001, pin 14; the one they should not use is P4006, pin 29. Whoever installed your GNS430W should fix this under warranty as it is their error. ----- I just purchased an Aztec with the same autopilot and an Avidyne IFD540.... and my avionics shop further suggested: ----- Maybe the GPS does not have labels enabled – that is pretty common and a second to correct. Need to look at the IFD540 configuration. Without WAAS and labels enabled it will not enable GPS Vertical Guidance ----- Hope this helps other people looking for the same information and I'll post back when I confirm the issue is resolved... hopefully!
If you have a glide slope coupler and when using GPSS and have the approach loaded, once established on the localizer, (the auto pilot should be in ALT mode, all four switches enabled), and then switch from Heading to Loc Norm mode. The Century III will take at least 20 seconds to couple the glide slope. When the Glide Slope Coupler light comes on, the autopilot WILL fly the glide slope. The same is true if you have WAAS on a RNAV WAAS approach. Once established, switch from Heading to Loc Norm mode and when the Glide Slope Coupler light comes on, it will fly the glide slope.
