Century 41 AP glide slope coupling

arkvet

arkvet

Line Up and Wait
Joined
Feb 8, 2016
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776
Location
Arkansas
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Display name:
Brent
Just wondering if anyone out there can help me troubleshoot my autopilot. Honestly it's probably a user error (me) which is why I seek advice here before calling autopilots central in Tulsa.

The 41 is a 3 axis AP. I have used it quite a but in standard heading mode and also in NAV mode for longer x countries. It is coupled with my 530W. I also have an HSI (NSD 360) that is fully functional that I use for the approaches.

Using the HSI and the 530W in GPS mode the AP will fly approaches no problem at all. I get notifications on my 530 to adjust the HSI pointer for course adjustments. I love it.

One issue that I have is that I've never been able to get it to automatically grab and fly the glideslope. I have the manual that explains the criteria for automatic capture and it just never happens. I can put it in approach mode and be at the correct altitude at IAF / FAF and I have to manually pitch down / descend.

I know my AP is capable of this but what I'm not sure of is what is the likely issue. Is the AP itself, the 530W info or the the HSI not sending the signal? OR is is user error?

I realize it's doubtful that anyone can give me a specific answer but wondering if just generating some discussion can maybe lead to figuring this out or at least figuring out where to get the answer.

Maybe in another year or two I'll just pull the HSI and vacuum AI and install an Aspen pro. All my problems should go away:)
 
arkvet said:
Just wondering if anyone out there can help me troubleshoot my autopilot. Honestly it's probably a user error (me) which is why I seek advice here before calling autopilots central in Tulsa.

The 41 is a 3 axis AP. I have used it quite a but in standard heading mode and also in NAV mode for longer x countries. It is coupled with my 530W. I also have an HSI (NSD 360) that is fully functional that I use for the approaches.

Using the HSI and the 530W in GPS mode the AP will fly approaches no problem at all. I get notifications on my 530 to adjust the HSI pointer for course adjustments. I love it.

One issue that I have is that I've never been able to get it to automatically grab and fly the glideslope. I have the manual that explains the criteria for automatic capture and it just never happens. I can put it in approach mode and be at the correct altitude at IAF / FAF and I have to manually pitch down / descend.

I know my AP is capable of this but what I'm not sure of is what is the likely issue. Is the AP itself, the 530W info or the the HSI not sending the signal? OR is is user error?

I realize it's doubtful that anyone can give me a specific answer but wondering if just generating some discussion can maybe lead to figuring this out or at least figuring out where to get the answer.

Maybe in another year or two I'll just pull the HSI and vacuum AI and install an Aspen pro. All my problems should go away:)
Click to expand...

I fly a C41 with a G500/GTN750 and have no issues with this, so yes, it works quite well. If I didn't break off my C41 above the landing the Bo would hit the concrete right on the center line.

I'll bet your problem is related to one of the following. I am assuming you have the right NAV radio and frequency selected.

1. Are you in NAV mode, and will the unit fly a 45 to enter an approach? If yes this confirms the logic in the computer is processing the signal received from the nav radio. If not, need to get this issue resolved first.

2. If your GPS switching from GPS mode to CDI mode on the approach?

3. At the FAF, if you're on altitude (and not fully deflected) and you press APR, do you see a GS light on the annunciator? If you are below or above altitude the unit will not lock in.

4. If you switch to your NAV2 radio, do you see any behavior change if you fly and press buttons the same way?

You said you read the manual, but let's review procedure.

GLIDESLOPE COUPLING - In the presence of selected APR mode only and other enabling logic, the glideslope function is fully automatic. Therefore, no GS engage switch is used. Glideslope may be entered from either ATT or ALT mode, from either above or below the glideslope. Capture of the glideslope depends upon satisfying conditions which will complete the arming sequence. After arming, capture will occur just before glideslope interception so as to rotate smoothly to interception. This “anticipative capture” point is determined by the rate of closure satisfying a computer equation. In order for the glideslope to arm, the following conditions must exist simultaneously:

1. No 1 NAV radio channeled to a localizer frequency.
2. Localizer deviation must be less than 80% of full scale.
3. A valid localizer signal (no flag).
4. A valid glideslope signal (no flag).
5. APR mode selected.

When these conditions are met the GS Annunciator will illuminate in conjunction with the active pitch mode light indicating glideslope is armed. When “anticipative capturing” occurs, the active pitch mode light will go out leaving only the illuminated GS annunciator to indicate that transition to the glideslope signal has occurred. The GS mode may be deactivated by selection of any other pitch mode (ALT, ATT, GA) but automatic recapture of the glideslope may occur in ALT or ATT modes. ATT 68S803 17 NOTES The NAV mode should be used when executing a holding pattern on the localizer to prevent automatic glideslope coupling. When radio receiver is tuned to a localizer frequency

Since you said in GPS mode the C41 will control the plane, we know what works to support this. Now we focus on the radio, signal, and the buttonalogy.

Let us know how you do.
 
Wow. Can thank you enough. I don't know that at this moment I can answer most of your questions. I'm going to print out your reply and take it with me next time up.

Just to give you more background I'm not IFR rated. I'm working on the rating and have been learning the AP while doing practice approaches in VMC of course. What I have been doing is going "direct to" my destination. Enroute choosing an RNAV approach and loading it. When I activate the APP the AP adjusts my course according to whatever IAF I choose. I don't have GPSS so I'm helping it along with the HSI pointer. The 530w will tell me to adjust course and age I spin the pointer the AP flies everything beautifully. Usually prior to the IAF I change to APP mode.

The 530 enters the frequencies for me and although I don't do it every time I have verified them to be correct.

I do not know if the GPS goes to CDI mode on the approach. Should it?

All I know is that the AP flies the approach perfectly but when I am beneath the glide slope on a perfectly aligned approach i don't capture the glideslope. The AP would fly my right across the #'s at altitude.

You've given me a ton to look at.

I admit I'm still learning this AP but understand it to be extremely capable of lightening the workload during single pilot IFR operations. I don't want it as a crutch but rather a very helpful copilot.

Thanks so much.

Brent.
 
I don't use a 530 so I do not know if it will switch from GPS to CDI automatically. My 750 does this. Bottom on the screen will show the mode. GPS or CDI.

Are you selecting an ILS approach, loading, and activating? Just checking.

The C41 is a very reliable and capable autopilot.
 
I have not been selecting an ILS approach. I fly mostly into smaller airports where RNAV is the best option. If I'm understanding you correctly I'm probably expecting the AP to capture the GS on an RNAV approach but since it's non precision it isn't going to? There are a couple ILS approaches not too far from me. I will try them and see if that is the issue.

Like is said in the original post... user error is a very probable culprit!

And yes I've noted the GPS / CDI toggle on the 530. I just haven't noted it changing during an approach.
 
ILS: Garmin 430/530 will only auto-capture if :

A) It's turned on in the Aux pages.
B) You intercept the ILS within 2-15 miles outside the FAF.

VOR: It will not auto-capture and must be switched manually.

I'd get into the books and understand the Garmin first before worrying about AP coupling it.

Your mileage may vary on any/all of the above if the Garmin isn't up to date on firmware. I don't know of any behavior changes on auto-capture over time with the firmware but there could have been some, and you'd have to research your specific version to know for sure.

Switching to an Aspen won't help if you're not cracking the books and operating the Garmin correctly... just as a side point.

I highly recommend Max Trescott's books on the various Garmin stuff if reading the AFM and all the Garmin supplements for the specific airplane and installation puts you to sleep. You'll still need to do that to make sure it's set up to do various things, but Max's books help with knowing what the box is capable of and how to use it which gives a baseline for determining if this particular installation acts in any way "abnormal".

Have fun with it. 430/530 will do a hell of a lot more than most people (including me) have all figured out.

The PC simulator is badly dated but can help a bit also.
 
arkvet said:
I have not been selecting an ILS approach. I fly mostly into smaller airports where RNAV is the best option. If I'm understanding you correctly I'm probably expecting the AP to capture the GS on an RNAV approach but since it's non precision it isn't going to? There are a couple ILS approaches not too far from me. I will try them and see if that is the issue.

Like is said in the original post... user error is a very probable culprit!

And yes I've noted the GPS / CDI toggle on the 530. I just haven't noted it changing during an approach.
Click to expand...

Go fly an ILS practice approach. That will confirm a number of things are working. We can then eliminate some component performance and focus in other areas.

Great doc on the various GPS approaches. http://www.faa.gov/about/office_org...nss/library/factsheets/media/RNAV_QFSheet.pdf
 
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