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Garmin A/P Issue…

R

RV12JT

Well Known Member
So, prior to takeoff on every flight, I religiously set my Garmin A/P, I enable FD, set VS, usually 500fpm, and set it to track Nav or Hdg, as desired.

Here is my issue…I take off and as I climb out I begin a steeper than 500fpm climb. Glancing at the G3X I see a higher rate of climb, it varies, maybe 600 or 800fpm climb. As soon as I notice the steeper angle, and before the speed warnings, I either disconnect and rearm. Sometimes I’m able to just rotate the up/ down wheel down a couple of hundred feet and all is back to normal.

Very perplexing, all parameters seem to be correct. Anyone with a Garmin 307/507 control unit have this issue?
 
RV12JT said:
So, prior to takeoff on every flight, I religiously set my Garmin A/P, I enable FD, set VS, usually 500fpm, and set it to track Nav or Hdg, as desired.

Here is my issue…I take off and as I climb out I begin a steeper than 500fpm climb. Glancing at the G3X I see a higher rate of climb, it varies, maybe 600 or 800fpm climb. As soon as I notice the steeper angle, and before the speed warnings, I either disconnect and rearm. Sometimes I’m able to just rotate the up/ down wheel down a couple of hundred feet and all is back to normal.

Very perplexing, all parameters seem to be correct. Anyone with a Garmin 307/507 control unit have this issue?
Click to expand...

When you look at the PFD and observe a vertical speed significantly in excess of 500 fpm, is the autopilot engaged and in VS mode vertically with the selected vertical speed cyan bug at 500 fpm?

VSModeAt500.png

Steve
 
Sounds like the Vertical Speed Gain was not properly tuned. Suggest you study and carry out the entire tuning procedure in Appendix A of the Installation Manual, which is autopilot tuning.
 
In addition....TOGA (Takeoff / Go-Around) is a much better mode to takeoff (and Go-Around) in. The following video describes a method to accomplish this. This results in a smooth transition (as long as the autopilot is tuned properly) with the least number of button pushes.

https://youtu.be/XLhtgA8P7Ow
 
I ran into similar issues, and here's my solution.

After takeoff, with the plane at a shallow climb attitude, I turn on the autopilot with all modes off. This puts the autopilot into pitch attitude and wings level. After the plane has accelerated, then I can adjust for desired climb, whether using pitch, airspeed, or vertical speed.

If ATC has given a heading to turn to after takeoff, I set that heading in but do not engage Heading mode until I'm ready to make the turn.

Similarly, for TOGA, I set that to a shallow climb so that the plane can accelerate. After the speed has increased, then I can put in a standard climb. There's no hurry to start the climb immediately, because the go around is like a takeoff but with an 80 knot head start.
 
Longez said:
When you look at the PFD and observe a vertical speed significantly in excess of 500 fpm, is the autopilot engaged and in VS mode vertically with the selected vertical speed cyan bug at 500 fpm?

View attachment 44701

Steve
Click to expand...

Yes and no. The VS is set, in most cases 500 fpm, but it now appears 800 fpm on my display. Normally I just rotate the wheel so the display again reads 500 fpm on the display and it usually settles aircraft back down to 500 fpm. There have been a few times where I needed to disconnect and re-engage the A/P, as lowering my rate didn’t take.

As a few others here (Thanks Gentlemen) have stated, I may have to check appendix A and check or recalibrate my settings. I’ll let you all know how I make pout. May also shoot an email to g3expert.

Thanks all,
John
 
RV12JT said:
Yes and no. The VS is set, in most cases 500 fpm, but it now appears 800 fpm on my display. Normally I just rotate the wheel so the display again reads 500 fpm on the display and it usually settles aircraft back down to 500 fpm. There have been a few times where I needed to disconnect and re-engage the A/P, as lowering my rate didn’t take.

As a few others here (Thanks Gentlemen) have stated, I may have to check appendix A and check or recalibrate my settings. I’ll let you all know how I make pout. May also shoot an email to g3expert.

Thanks all,
John
Click to expand...

So, this is not a VS gain issue. Some how your VS target is changing from 500 to 800. I have never seen this, but never use VS in a climb and never right after TO. However, I do use it all the time for descents from cruise. I have NEVER seen the VS change once set for a decent and the AP engaged. I have a 307. I have, on occasion doing approach work, seen the armed setting a bit different than what they were when I last disconnected the AP, so do wonder if there may be some S/W logic that changes the armed settings sometimes. FOr example, if you arm the VS for 500 FPM, but are actually climbing at 800 FPM, there may be a config setting that is telling the S/W to change the VS target from the armed setting to the current actual VS when the AP is activated. I vaguely remember a few different config settings along these lines.
 
Last edited:
RV12JT said:
Yes and no. The VS is set, in most cases 500 fpm, but it now appears 800 fpm on my display. Normally I just rotate the wheel so the display again reads 500 fpm on the display and it usually settles aircraft back down to 500 fpm. There have been a few times where I needed to disconnect and re-engage the A/P, as lowering my rate didn’t take.

As a few others here (Thanks Gentlemen) have stated, I may have to check appendix A and check or recalibrate my settings. I’ll let you all know how I make pout. May also shoot an email to g3expert.

Thanks all,
John
Click to expand...
John,

Do you engage the autopilot by pressing and holding the CWS button, or by pressing the AP button on the GMC?

I don't use the CWS button to engage the autopilot (just the AP button on the GMC), but I wonder if you are using the CWS button if it might be affecting the VS setting you selected on the ground.

Steve
 
Longez said:
John,

Do you engage the autopilot by pressing and holding the CWS button, or by pressing the AP button on the GMC?

I don't use the CWS button to engage the autopilot (just the AP button on the GMC), but I wonder if you are using the CWS button if it might be affecting the VS setting you selected on the ground.

Steve
Click to expand...

There are a handfull of settings to determine what the AP will do when the CWS button is pressed, including a default VS, IIRC, though that may have been my GRT setup. Suggest reading the manual to understand each of them. They were not highly intuitive and required a good bit of experimentation to get it to behave the way that I wanted it to when I first started testing it.
 
Traash said:
In addition....TOGA (Takeoff / Go-Around) is a much better mode to takeoff (and Go-Around) in. The following video describes a method to accomplish this. This results in a smooth transition (as long as the autopilot is tuned properly) with the least number of button pushes.

https://youtu.be/XLhtgA8P7Ow
Click to expand...

Joe,
At what point do you press the TO button?
I have the TO/GO and have used it in a missed approach but never on the take off and not sure of its operation.
Do you press TO/GO first and then activate the A/P or the other way around?
 
TOGA is selected during the pre-start flow and checked in the before start checklist.
 
Open the Black Box. See what is happening.

To the OP - - If you have Garmin EFIS, look at the flight data file, it will have the AP controls inputs and outputs. The trim and torque will be included. You can analyze what is happening or not happening. If the AP is in VS mode and set to 500, the data will report that. It is tedious but this file will have everything you need to know what and why it is happening without having to make adjustments not knowing why.
 
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