Avidyne Homepage
Forum Home Forum Home > Avidyne General > IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM
  New Posts New Posts RSS Feed - Autopilot not flying courseline on approach
  FAQ FAQ  Forum Search   Register Register  Login Login

Autopilot not flying courseline on approach

 Post Reply Post Reply Page  <12
Author
Message
Cruiser View Drop Down
Newbie
Newbie
Avatar

Joined: 24 Feb 2017
Location: Ohio
Status: Offline
Points: 33
Post Options Post Options   Thanks (0) Thanks(0)   Quote Cruiser Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2018 at 9:46am
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.
Back to Top
Bob H View Drop Down
Groupie
Groupie


Joined: 26 Jan 2018
Location: NH - KMHT
Status: Offline
Points: 48
Post Options Post Options   Thanks (0) Thanks(0)   Quote Bob H Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2018 at 1:06am
This is an interesting discussion on how systems interface and how they should be used to fly an approach, especially precision approaches.  For my own understanding and learning, I’ve summarized some of the information from this thread combined with my own thoughts of how things work.  Please let me know if there is any disagreement.

1.       The IFD never knows what state the autopilot is in, i.e. HDG, GPSS, NAV, APPR, HI, LO, etc.
2.       GPSS only functions when the autopilot is in HDG mode.  If HDG mode is not active, then it makes no difference what state GPSS is in.  Therefore, if the autopilot is in HI TRK mode, turning off GPSS will have no effect on anything.
3.       Nothing external to the IFD will affect or change its CDI sensitivity.
4.       The IFD GPSS can only output enroute CDI sensitivity.
5.       A coupled precision approach should only be flown in APPR (HI TRK) mode inside the FAF. 

Any corrections?

Bob
Back to Top
paulr View Drop Down
Senior Member
Senior Member


Joined: 24 Jan 2014
Status: Offline
Points: 245
Post Options Post Options   Thanks (0) Thanks(0)   Quote paulr Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2018 at 7:45am
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?
Back to Top
HenryM View Drop Down
Groupie
Groupie


Joined: 13 Oct 2017
Location: Texas
Status: Offline
Points: 98
Post Options Post Options   Thanks (0) Thanks(0)   Quote HenryM Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2018 at 8:14am
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. 
Back to Top
Bob H View Drop Down
Groupie
Groupie


Joined: 26 Jan 2018
Location: NH - KMHT
Status: Offline
Points: 48
Post Options Post Options   Thanks (0) Thanks(0)   Quote Bob H Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2018 at 8:45am
Originally posted by HenryM 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. 
That is how it works in my setup as well.  Here is a modified diagram from Page 1 of this thread.  When the AP is not in HDG mode, the HDG/GPSS signal does nothing.

Bob
Back to Top
oskrypuch View Drop Down
Senior Member
Senior Member


Joined: 09 Nov 2012
Location: CYFD
Status: Offline
Points: 2251
Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2018 at 8:48am
Quote 4.       The IFD GPSS can only output enroute CDI sensitivity.

I understand your intent with the statement, but perhaps it is 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



Edited by oskrypuch - 22 May 2018 at 10:34am
Back to Top
Bob H View Drop Down
Groupie
Groupie


Joined: 26 Jan 2018
Location: NH - KMHT
Status: Offline
Points: 48
Post Options Post Options   Thanks (0) Thanks(0)   Quote Bob H Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2018 at 9:17am
Originally posted by oskrypuch oskrypuch wrote:

Quote 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?

4. The IFD output used by the GPSS module only outputs enroute sensitivity.  IFD Course Deviation output does change from enroute, to terminal, to approach sensitivity, both LNAV & APV, as the situation dictates.
Bob
Back to Top
oskrypuch View Drop Down
Senior Member
Senior Member


Joined: 09 Nov 2012
Location: CYFD
Status: Offline
Points: 2251
Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2018 at 10:35am
Originally posted by Bob H Bob H wrote:

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

4. The IFD output used by the GPSS module only outputs enroute sensitivity.  IFD Course Deviation output does change from enroute, to terminal, to approach sensitivity, both LNAV & APV, as the situation dictates.

Looks perfect to me.

* Orest
Back to Top
 Post Reply Post Reply Page  <12
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.

This page was generated in 0.043 seconds.