Autopilot not flying courseline on approach

snip....


In the problem I was having with the deviation at a one mile final, the Aspen was in GPSS mode, the autopilot was in HD mode, and there was no fixes or transitions at that point.  With the Aspen off of GPSS mode, the autopilot in HI TRK mode inside the IAF, the approach was right on the numbers.
[/QUOTE]


I still don't understand what was loaded in the IFD? On the FMS page you can see the route that is loaded and the active segment as you move along your course. What was the next waypoint (active) you were steering to?


On the S-TEC System 30 the HD mode will follow the heading bug on your HSI/DG.

Switching modes to LO is the same as going from HDG to NAV on other autopilots.
Switching modes to HI is the same as going from NAV to APR on other autopilots.


Both LO and HI switch the source of signal to the navigation unit supplying the course data.
HD mode switches the source data to the heading bug.

I'm a little confused by #2. I would think the AP will follow whatever course deviation signal it gets. I know that when my AP is in HDG mode, it's getting steering data from CDI 1-- which is driven by the IFD. Whatever nav source the IFD uses is reflected on CDI 1, and thus passed to the AP. If I change the AP to another mode (say LOC), it's still going to follow the deflection on the CDI, wherever it comes from, right?

HenryM wrote: In HD mode, my STEC-30 AP follows whatever heading error is provided by the Heading system. This signal can come from a Directional Gyro with a heading bug, or it can come from a GPSS system. The CDI is not the source of the error signal.  The CDI is the source of the error signal that tells the AP to turn when the STEC-30 is in TrkLo (NAV) or in TrkHi (APPR) modes.

oskrypuch wrote: 4.       The IFD GPSS can only output enroute CDI sensitivity. I understand your intent with the statement, but perhaps it si a bit misleading -- using the term GPSS (vice GPS course deviation, the magenta line). There is of course no GPSS facility within the IFD. The other comment, the GPS course deviation actually can/will change from enroute, to terminal, to approach sensitivity, both LNAV & APV, as the situation dictates. * Orest

Yes.  Thanks for precision with my wording to avoid confusion.  If I may steal some of your wording, how is this for #4?

HenryM wrote: Was the heading bug set to the actual course you were flying? As Cruiser suggests, maybe the Aspen is switching the heading source for some reason.  If you are in HiTrk mode, I’m not sure you need to switch GPSS off.