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G3X AP ALT Hold issue

J

jquayle

Member
I think I'm having some odd AP behavior. What Garmin is telling me and what their training videos state don't seem to agree.

When flying in ALT hold (ALT selected on the AP) and the G3X displaying ALT and my altitude (For example ALT 7500) I believe I should be able to change the altitude preselect and the AP should continue to hold 7500 until I change from ALT to another mode (VNAV, VS or IAS).

However, as soon as I start to change altitude preselect the AP immediately start flying to that altitude at about 300fpm. It does this if I dial it up or down. It also does this if the AP went into ALT mode after reaching an altitude in another mode (like VS or IAS) and then locks onto that altitude or if I'm just flying and hit the ALT button.

The Garmin G3X AP training video says the AP should hold altitude when in ALT mode until I change to another mode.

https://tinyurl.com/G3X-AP-ALT

When I called Garmin they told me this behavior of immediately chasing the new altitude was normal. My guess is that theirs a configuration setting somewhere that I need to change. In the video they mention "If you're configured like a certified aircraft" which leads me to believe that this is an option available only to the experimental APs but the information Garmin send me was just pointing to the Pilot's Guide and didn't reference this issue.

Anyone have any insight? Does this behavior match others with the G3X?


Thank you,


Jeff
 
Garmin A/P

I’m sure others will give a more complete answer (Matt B) but mine holds altitude until I hit the VS button to tell it how to get there.
 
jquayle said:
I think I'm having some odd AP behavior. What Garmin is telling me and what their training videos state don't seem to agree.

When flying in ALT hold (ALT selected on the AP) and the G3X displaying ALT and my altitude (For example ALT 7500) I believe I should be able to change the altitude preselect and the AP should continue to hold 7500 until I change from ALT to another mode (VNAV, VS or IAS).

However, as soon as I start to change altitude preselect the AP immediately start flying to that altitude at about 300fpm. It does this if I dial it up or down. It also does this if the AP went into ALT mode after reaching an altitude in another mode (like VS or IAS) and then locks onto that altitude or if I'm just flying and hit the ALT button.

The Garmin G3X AP training video says the AP should hold altitude when in ALT mode until I change to another mode.

https://tinyurl.com/G3X-AP-ALT

When I called Garmin they told me this behavior of immediately chasing the new altitude was normal. My guess is that theirs a configuration setting somewhere that I need to change. In the video they mention "If you're configured like a certified aircraft" which leads me to believe that this is an option available only to the experimental APs but the information Garmin send me was just pointing to the Pilot's Guide and didn't reference this issue.

Anyone have any insight? Does this behavior match others with the G3X?


Thank you,


Jeff
Click to expand...
Jeff,

You will want to review page 329 of the current Rev. V G3X Touch Pilot Guide.

It sounds like someone has set your "ALT Mode User Up/Down Action" field to "Select VS Mode" instead of the default "Normal" setting which will have the behavior you (and most of us) desire.

Steve
 
Steve is correct, there are various user-configurable options that affect how the G3X flight director works in altitude hold mode. Different people seem to have different preferences about how it should work, so for those who don't like the default behavior it's nice to have it be configurable. Sounds like you have inadvertently changed one of these settings. Specifically, it sounds like you might have "Altitude Controls" set to "Simplified":

When Altitude Controls are set to Simplified, Altitude Hold (ALT) Mode behavior differs in the following ways:

  • Selecting Altitude Hold (ALT) Mode causes the Selected Altitude (Altitude Bug) to change to the current aircraft altitude.
  • There is no longer a difference between the Selected Altitude (Altitude Bug) and the Target Altitude for Altitude Hold (ALT) Mode.
  • After Altitude Hold (ALT) Mode captures the Selected Altitude, subsequent changes to the Selected Altitude will cause ALT Mode to climb or descend towards the new Selected Altitude.
  • Subsequent vertical speed adjustments are in increments of 100 fpm, with the exception the user cannot adjust the target vertical speed to a value that would cause the aircraft to fly away from the Selected Altitude.
  • Unlike Select VS Mode described previously, this option does not switch to VS mode. Instead, it displays a vertical speed bug.
  • The initial vertical speed used for climb or descent towards the new altitude is determined by the Default Vertical Speed fields as described previously.
  • When Altitude Hold (ALT) Mode has captured the Selected Altitude, the vertical speed bug is removed and vertical speed adjustments have no effect.
Click to expand...

The above is from the G3X Touch Pilot's Guide.
 
Last edited:
That was it!

Matt,

Thank you. That's exactly what's going on. Garmin had pointed me to an entirely different section of the pilots guide and I wouldn't have guessed the answer was in the Flight Director Operation section.

I recently purchased this plane and apparently the previous owner preferred this simplified method. He wasn't instrument rated, so perhaps he felt this was easier for VFR flight.

Thank you again!



Jeff
 
mburch said:
Steve is correct, there are various user-configurable options that affect how the G3X flight director works in altitude hold mode. Different people seem to have different preferences about how it should work, so for those who don't like the default behavior it's nice to have it be configurable. Sounds like you have inadvertently changed one of these settings. Specifically, it sounds like you might have "Altitude Controls" set to "Simplified":



The above is from the G3X Touch Pilot's Guide.
Click to expand...

Just when I thought I had mastered the G3X Touch...
 
Never knew about this either. One more thing to play around with... Always something...
 
One of the insidious gotchas with all this configurability is that a pilot could get into another plane with the same system and be surprised if the system acts differently because of a different configuration.

The configuration might also be changed inadvertently by an avionics shop working on the plane. One source recommends saving the configuration beforehand. They also recommend saving any switch setting that you always expect to be in the right place.
 
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