GFC-500 question

[jsstevens]

Flying in a plane equipped with a G-500, twin GI-275s and a GFC-500 autopilot, I had taken off and was established on course and in the climb. I turned on the autopilot and placed it in NAV mode. I did not turn on any of the altitude section. I saw that the cylinder head temp was creeping up on once cylinder. Since I was already running full rich in the climb, I tried to ease the nose down a bit to get more airflow. The autopilot wouldn't let me. (I'm sure I could have pushed hard enough to make it let go but I didn't want to break any thing.)

How come? I finally put it in IAS mode for altitude and it properly maintained the IAS until we reached our bugged altitude and it leveled off.

Just trying to understand. And the CFI riding with me had no idea.

John

 

[jrcox19]

What vertical mode were you in initially? Don't say "none" because that's not an option.

Hint, if you didn't select anything, it probably went into pitch hold mode.

 

[Radar Contact]

My understanding is you turned the AP on and it captured current pitch and bank. Then you selected nav and that controlled the lateral. You were still in pitch mode. Gently pushing wasn’t going to do anything. You needed to CWS and reset pitch or push hard to disconnect the AP. When you selected IAS you were no longer in pitch mode.

PS. You should never be scared of breaking something. It’s designed for you to overpower the servos. Practice it on the ground and get a sense of the force. If it’s not possible you need to not use it till fixed in my opinion.

 

[jsstevens]

Thanks. Pitch hold sounds like what it did.

And I suppose I should t say afraid to break something, just didn’t need to do it and did t understand what was happening.
Thanks!

 

[AggieMike88]

Thanks. Pitch hold sounds like what it did.

And I suppose I should t say afraid to break something, just didn’t need to do it and did t understand what was happening.
Thanks!

If you’re not already doing this habit, it helps and it is what was beaten into my brain about auto pilots.

Each time you touch the AP to turn on or change something, verify the annunciation details in the “scoreboard” on your PFD.
​

This line of data should be showing you what’s happening for both lateral and vertical and can either verify all is well or aid in determining what’s not right.

 

[CT583]

When you bug an altitude, you’ll need to hit IAS or VS then use the wheel to select your rates.

I did this same thing a few times when getting used to the system. When in doubt, hit the AP and reset your desired values.

 

[Groundpounder]

If you don't select IAS or VS it will automatically default to pitch mode. If you deselect IAS or VS it will go back to pitch mode. It can be adjusted with the wheel on the MCP.

 

[jsstevens]

If you don't select IAS or VS it will automatically default to pitch mode. If you deselect IAS or VS it will go back to pitch mode. It can be adjusted with the wheel on the MCP.

And that was the missing piece of my knowledge. Default to pitch mode.