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A/P will not switch to HDG mode when internal GPS is active

Postby smbohn » Sun May 13, 2018 12:07 pm

Testing out my newly installed GRT Autopilot with Horizon HX EFIS (V9 software.) GNAV works flawlessly (both on the ground and in the air.)

The problem I have is this: I was ground testing yesterday and could not get the HDG mode engaged. When I activate the A/P in HDG mode, it appears to briefly go in to HDG mode and then immediately switch to GNAV or ENAV. Every time.

Any ideas?

Steve
N44VF
Velocity XLFG
smbohn
 
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Re: A/P will not switch to HDG mode when internal GPS is act

Postby smbohn » Mon May 14, 2018 8:40 pm

After additional testing, I was able to determine that I can't select HDG mode when GPS2 (the internal GPS) is active.

After powering up the EFIS, the A/P will be in HDG mode until the internal GPS activates. At that point it will switch to ENAV mode and stay there.

Here is a link to a video of the situation:
https://www.dropbox.com/s/da21rrifz1x5wrv/N44VF%20AP%20Operation.mp4?dl=0

A little more background on the EFIS set up: The panel has three EFIS. From left to right, they are labelled DU2, DU1, DU3. The A/P servos are connected to Serial 8 of DU2 (the left most unit) and only to that unit.

Some operational aspects of the system seem strange:

1. DU1 and DU3 can display the A/P menu, however they can't engage the A/P. Engaging the A/P can only be done from DU2.
2. When invoking the A/P from the soft keys, the "LAT A/P" softkey is only displayed on DU1. DU2 and DU3 only show the "VERT A/P" softkey. See this video: https://www.dropbox.com/s/u798e1nr9os4nnh/N44VF%20Missing%20LAT%20AP%20softkey.mp4?dl=0
smbohn
 
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Re: A/P will not switch to HDG mode when internal GPS is act

Postby GRT_Jeff » Tue May 15, 2018 7:45 am

Check the Analog # Function settings in SET MENU, General Setup, after the serial ports. The screen that's missing the LAT A/P button probably has an analog function set to "Ext A/P HDG Mode Select (direct)". Change it to Off.
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Re: A/P will not switch to HDG mode when internal GPS is act

Postby smbohn » Mon May 21, 2018 5:41 pm

Hi Jeff... I finally got to the hangar this past weekend and you were spot on.

According to the wiring diagrams (which may be a bit dated) the OBS Annunciation (P1001-14) from the GTN 650 is wired in to Analog 4 (B-18.) When I changed the function to 'Off', I was able to engage in HDG mode.
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Analog 1-4 Setup Options SM.jpg
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