G1000 autopilot has problems intercepting the glide scope on ILS approach?

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1

Hi. This is really weird and has happened to me a few times already with the Cessna 172, G1000. I have the ILS properly tuned in NAV 1, I have clicked AP to “On,” and I have clicked the APR button to “On.” I have also changed CDI to the first VOR, which is for ILS. So the autopilot will align my Cessna 172 horizontally with the ILS approach, which is great and this aspect of the autopilot is working.

However, I am below the glide scope. At this point, I expect the autopilot to fly straight until it intercepts the glide scope, at which point it should pitch down 3 degrees to continue on the glide scope (I have enough throttle set for the Cessna 172 to fly straight or even climb). But instead, the altitude of my Cessna 172 keeps decreasing until I am about to hit the ground.

Is this a bug with the autopilot? Or am I doing something wrong that is preventing the autopilot from intercepting the glide scope?

2

Are you keeping ALT hold on during the approach? I think it then goes out once it starts to decend off the glidescope.

3

I didn’t click the ALT button at all. I don’t really use the ALT button (I use FLC to keep me at a specific altitude).

4

Ah, so then there you go. I have never used FLC and have never had a problem intercepting GS. So I am betting that is the problem.

5

Oh, ok. I’m pretty sure I have FLC off when I click on APR but I can double check again.

6

You need something to hold your altitude before it decends on it’s down. I suggest using the ALT to hold your altitude during the approach phase.

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7

Ahh, I see. So the autopilot for the G1000 isn’t capable of initially intercepting the glide scope on its own. So I need to keep the Cessna 172 at a steady altitude until the glide scope is intercepted, and then the autopilot for the G1000 will automatically descend. Thanks, if that that is the missing step, then it makes sense!

8

Right, also you have to be at the right angle to intercept the glidescope as well. I think it shows a GS on the Garmin up top and the diamond will show on the right by the Altitude meter. Approach mode tells the Garmin to look for the glidescope and act upon it but it takes a bit of time so you need to hold your altitude until it acts upon its own.

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9

I see. I thought the autopilot for the G1000 was more sophisticated than it really is but I guess I have to “hold the hand” of the autopilot a little in ILS approaches.