Glide slope slow to activate

Morgan3820

Morgan3820

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El Conquistador
I was up today playing around in the clouds. On a couple of ILS approaches the glide slope did not capture until the FAF, or in one case it failed to capture completely. Fortunately, I was VMC at that point, but still. I have an IFD440 with a Garmin 106B. The localizer was fine. No error flags. The IFD was tuned to the localizer frequency. Any ideas?
 
Morgan3820 said:
I was up today playing around in the clouds. On a couple of ILS approaches the glide slope did not capture until the FAF, or in one case it failed to capture completely. Fortunately, I was VMC at that point, but still. I have an IFD440 with a Garmin 106B. The localizer was fine. No error flags. The IFD was tuned to the localizer frequency. Any ideas?
Click to expand...

By capture I assume you mean the Autopilot. What Autopilot?
 
No autopilot. The glide slope indicator bar either never indicated or was late in doing so. i am having difficulty in my terminology.
 
I thought you meant you didn’t get a glideslope at all, but I’m confused by “activate”, “capture”, and “no flags”
 
I’ve had glideslopes not pop up Until just after the FAF.
 
Morgan3820 said:
No autopilot. The glide slope indicator bar either never indicated or was late in doing so. i am having difficulty in my terminology.
Click to expand...
Was the GS needle stuck fully deflected upward? Or was it stuck fully deflected downward? Or was it stuck in the middle?

And when you say no flags, you mean that you didn't see that orange thing on the right and on the bottom, correct? Do they appear when everything is turned off? Where is the GS needle when everything is turned off?
gi-106a-sv.jpg

Also, does the IFD have a self test mode where it wiggles the needles and flags on the GI106A?
 
asicer said:
Was the GS needle stuck fully deflected upward? Or was it stuck fully deflected downward? Or was it stuck in the middle?

And when you say no flags, you mean that you didn't see that orange thing on the right and on the bottom, correct? Do they appear when everything is turned off? Where is the GS needle when everything is turned off?
gi-106a-sv.jpg

Also, does the IFD have a self test mode where it wiggles the needles and flags on the GI106A?
Click to expand...
The gs needle was stuck in the middle. The gs flag was evident until it started indicating. Yes there is a self test where the needles deflect up and to the right, iirc.
 
It's hard to deduce from your written description, so I could be completely misunderstanding you -- but it sounds like your indicator or receiver may be malfunctioning. Under normal circumstances, a properly flown ILS approach will include capturing the glideslope from below. The correct indication would be full-scale up deflection, slowly decreasing until you're on the glideslope at the indicated altitude at the non-precision FAF. The glideslope should not suddenly appear to become "active" at that time.
 
OK, let me see if I get this straight:
  1. Power up, needles wiggle, flags toggle.
  2. Go out and fly, needles stuck in the middle, orange flags visible.
  3. Start an approach, orange flag for lateral disappears, lateral needle alive, orange GS flag still there, GS needle stuck in the middle.
  4. Fly the approach, GS flag disappears, GS needle stuck in the middle.
  5. No change to the GS flag/needle until MAP.
Did I miss anything?
 
asicer said:
OK, let me see if I get this straight:
  1. Power up, needles wiggle, flags toggle.
  2. Go out and fly, needles stuck in the middle, orange flags visible.
  3. Start an approach, orange flag for lateral disappears, lateral needle alive, orange GS flag still there, GS needle stuck in the middle.
  4. Fly the approach, GS flag disappears, GS needle stuck in the middle.
  5. No change to the GS flag/needle until MAP.
Did I miss anything?
Click to expand...
Pretty much it.

I went up again and did an RNAV approach. Everything worked fine for the RNAV approach. I activated the approach about 12 miles out and it went right to approach mode.
Just when doing the ils approach, the navigator forgets or is slow to change over from gps navigation to the ils.
I am beginning to think that it is something in the navigator unit. Not the cdi.
 
Morgan3820 said:
I went up again and did an RNAV approach. Everything worked fine for the RNAV approach. I activated the approach about 12 miles out and it went right to approach mode.
Just when doing the ils approach, the navigator forgets or is slow to change over from gps navigation to the ils.
I am beginning to think that it is something in the navigator unit. Not the cdi.
Click to expand...
Ah yes, forgot to ask whether the "GPS" or the "VLOC" annunciator is lit on the GI-106. That's an important bit of information.

gi-106b.png


Sounds like you're on track to figuring it out, though.
 
I think I would start by ensuring that all antennas and their connections are in good shape.
 
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