GS armed but not captured on ILS approach

[Yariv]

Hi,

today I confirmed on a second flight that there is a problem with the GS capture. I flew the approach using the GFC 700 autopilot, I was at glide slope intercept altitude long before the FAF but the GS stayed white (armed). I disconnected the AP and noticed the GS appeared momentarily but disappeared again. I then flew the localizer instead.

the second approach was a GPS approach and the GP (glide path) was captured successfully. 
Where should I look?

thank you,

Yariv

[LANCECASPER]

9 hours ago, Yariv said:

Hi,

today I confirmed on a second flight that there is a problem with the GS capture. I flew the approach using the GFC 700 autopilot, I was at glide slope intercept altitude long before the FAF but the GS stayed white (armed). I disconnected the AP and noticed the GS appeared momentarily but disappeared again. I then flew the localizer instead.

the second approach was a GPS approach and the GP (glide path) was captured successfully. 
Where should I look?

thank you,

Yariv

I would first double-check the NOTAMs at that airport to make sure that there wasn't any problems with the ILS. Then try an ILS approach at another airport just to make sure that you're not spending money chasing a problem that doesn't exist.

[StevenL757]

20 minutes ago, LANCECASPER said:

I would first double-check the NOTAMs at that airport to make sure that there wasn't any problems with the ILS. Then try an ILS approach at another airport just to make sure that you're not spending money chasing a problem that doesn't exist.

Agree.  Sometimes, the ILS needs to be reset as it can “drop out”.  This has happened more than once at JFK…where we’ve had to request the ILS be reset.  Sometimes it happens before they can actually NOTAM it as out or partially out.

[Yariv]

The 2 approaches were in 2 different airports - kpae and kpwt, on different days. I was not aware of relevant NOTAMs. 

[StevenL757]

4 hours ago, Yariv said:

The 2 approaches were in 2 different airports - kpae and kpwt, on different days. I was not aware of relevant NOTAMs. 

Were you in GPS (magenta line) or VOR/LOC (green line) mode at the time?  (had to ask)

[Yariv]

The G1000 in my airplane is configured to switch automatically from GPS CDI to the VAV1 or NAV2 LOC CDI before reaching FAF. I remember verifying that it switched correctly to the correct frequency and CDI needle. The GS was armed (white) and stayed like that as I crossed the FAF. Localizer was working fine.

[Browncbr1]

I believe there is a minimum distance from the FAF that app mode must be enabled for it to capture the GS.  How far were you from the FAF when you intercepted the final course and pressed app?

[Yariv]

3 hours ago, Browncbr1 said:

I believe there is a minimum distance from the FAF that app mode must be enabled for it to capture the GS.  How far were you from the FAF when you intercepted the final course and pressed app?

About 6 miles out before FAF

[EarthboundMisfit]

Maybe mount a camera to grab video footage of the PFD on the next ILS approach? 

Was the AP set to APR mode prior to intercepting the glideslope?

[Browncbr1]

8 hours ago, Yariv said:

About 6 miles out before FAF

That should be enough.  You intercepted under the gs, right?

 

 

 

[David Lloyd]

I've experienced the same problem, both LPV and ILS.  GI275s, GNX375, KX165, Stec 60-2.  Sometimes captures the glideslope, sometimes not.  Rebuilt mode controlller, rebuilt roll computer, exchanged pitch computer. wiring checked and rechecked, same results.  One techie at Garmin told me it was a known problem.

The Database Concierge has not worked properly between my iPad with Garmin Pilot, the 275s and 375 since February.  It will update one database at a time but not two or more.  They know about that also and prefer to let us spend time, money and frustration attempting to track down our problem rather than just fessing up.

[Yariv]

4 hours ago, Browncbr1 said:

That should be enough.  You intercepted under the gs, right?

 

 

 

Since I was at the intercept altitude 6 miles out, yes the interception is from below.

[Yariv]

10 hours ago, EarthboundMisfit said:

Maybe mount a camera to grab video footage of the PFD on the next ILS approach? 

Was the AP set to APR mode prior to intercepting the glideslope?

Yes, APR pressed once cleared for the approach, before intercepting the localizer. 

[GeeBee]

Did you try doing a manual GS intercept then engagement of the GS function? 

[Yariv]

27 minutes ago, GeeBee said:

Did you try doing a manual GS intercept then engagement of the GS function? 

by manual you mean toggling the ALT button? I tried that.

[GeeBee]

Yes, I did. Sounds like your autopilot has a failure to communicate with the needles.

 

[PT20J]

This can happen with discrete components when the ILS energize signal from the navigator doesn’t make it to the AP due to a miswire or bad connector pin. But I don’t know if there is any external wiring for this function on  the integrated G1000/GFC 700. Also, I think this would also preclude LPV GP capture. Sounds like a question for a Garmin dealer. I would call Rachel at Crown at KPAE. 

Skip

[Yariv]

2 hours ago, PT20J said:

This can happen with discrete components when the ILS energize signal from the navigator doesn’t make it to the AP due to a miswire or bad connector pin. But I don’t know if there is any external wiring for this function on  the integrated G1000/GFC 700. Also, I think this would also preclude LPV GP capture. Sounds like a question for a Garmin dealer. I would call Rachel at Crown at KPAE. 

Skip

Hey Skip, I think we just met recently at the airport:-). I did exactly that - called Garmin and then Rachel.

The plan now is to do another flight and try the GS once again on both NAV radios and take a video maybe. Would you like to be the safety pilot?