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Lost Vertical Autopilot

Postby gdtrfb58 » Sun Mar 01, 2015 2:43 am

HXr with GRT servos. Garmin GNS480.

Was working fine last time I flew (~6 weeks ago). Today, Lateral guidance fine in all modes. Every time I open AP menus, Vertical shows "off". No matter what mode I set, it never engages. (Shows "Vert Off" on PFD. It seemed to sometimes briefly show engaged, but the servos never did anything.). I went to the A/P section of the settings page. Everything communicating. Even so, I reset the breaker. Still no joy.
Today (next day) I pulled the nose cover (Velocity-Servo is mounted on canard) and powered up. I thought I saw the servo move initially, but no other control/EFIS manipulation caused it to move after that. As above, each time I engage the autopilot, the EFIS still shows vertical in Standby. Changing the setting in the Vertical Autopilot softkey menu does nothing,
Related info?: OAT 20 deg F.
I installed the latest GRT HXr software update since the last time I flew.
Posts: 58
Joined: Wed Mar 13, 2013 1:17 pm

Re: Lost Vertical Autopilot

Postby GRT_Jeff » Fri Mar 06, 2015 6:12 am

On the ground, you can't engage the vertical mode normally. The EFIS refuses to compute a vertical command without airspeed. To test the servo movement, you can use the Pitch Servo Direction setting in the SET MENU, A/P Maintenance page. Make a note of the setting in case you accidentally change it. Activate the setting with a knob, and then just push the knob without changing the setting to continue to the movement test. When you're done, make sure it's still set to the correct direction.

The reason why a servo disengaged is reported in the STATUS inset and the status box on the ENG/MAP page. If there's a stuck disengage signal or something like that you should see it there. If a servo says "Reporting Not Engaged", that usually means it's not receiving a command or the EFIS couldn't compute one in the current conditions.
Posts: 617
Joined: Tue Dec 11, 2012 12:11 am

Re: Lost Vertical Autopilot

Postby gdtrfb58 » Sat Mar 07, 2015 11:39 pm

Well, after much discussion with Tech support, we decided that the shear screw was likely broken. I waited and received the new screw today in the mail and went to install it.
~15 degrees warmer today. Shear screw is intact.
I followed the procedure above and the servo moved normally. I didn't get a chance to fly (digging out from the snow). I wonder if this was temperature related?
Posts: 58
Joined: Wed Mar 13, 2013 1:17 pm

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