Glide slope not coming in

[Houman]

Ok, I'm just starting to do some IFR training and yesterday with my instructor, we did some approaches, VOR, VLOC and trying to capture the glide slope on the ILS ( HSI ).

 

I have a GTN 650, coupled with my HSI.

 

What ever we did, we were unable to capture the ILS glide slope, the flag on the glide slope in the HSI instrument always stayed on, even after tuning the right nav frequency for ILS and verifying it.

 

I think it is something we are not doing right, the GTN 650 pilot manual is not very helpful on this, wondering what am I missing, since my instructor was not able to figure it out either.

 

Thanks for any advice or hints...

[MooneyBob]

Did you try LPV approach too? Did glide slope work? And I am pretty sure you know that but the unit has to be in the VLOC mode not in the GPS mode in order to do ILS. 

[Houman]

Yep, in Vloc mode, but ILS glide scope flag was still there. I'm wondering if this ever worked, it's my 1st tries in the IFR realm since buying the plane and having a GTN 650 installed last year.

[carusoam]

The flag is a bit of a telling indicator...

Either the settings are not set up properly or the connections need to be cleaned or something like that.

The flag is telling you that it is not receiving something that it needs to provide a solution

When tuning the ILS did you receive/hear all of the morse codes? 3:1 ILS:G/S (my memory is really old).

Did you have the opportunity to review the system operation protocol? Some systems may require the interception of the glideslope from underneath before the auto coupling can begin. When this is going correctly, the bars start at the top as the G/S is over head...

Do you have any odd switches like a source selector that is not set properly. With a GTN, the ILS and WAAS GPS are internal to one box. In older systems GPS and ILS are selected with an external switch. If you have an odd blue light on your panel, this is a relic from the 90s. The blue light illuminates when the GPS is the source. No-light, the nav/com is the source or the bulb is dead...

For anyone doing a PPI on a complex plane with updated nav/com equipment, add these to the list of things to test...

This is based on really old memories. Hope it helps...

Best regards,

-a-

[Seth]

When the system turns on, is the glide slope showing during the self test or is it "hung up" and not in view?

 

I had to have mine repaired.  It was gummed up and getting "caught" until turbulance/flying/bouncing along would set it free.  The AP would fly the glide-slope in both ILS and RNAV modes, but I would not see the indicator.  So the signal was coming in and causing the AP to intercept the slope, but I couldn't visually see it.  

 

The first time, I noticed it, it was during a practice approach, and my other radio was tuned to the ILS frequency so I saw that we were on glide slope on my secondary indicator.

 

I had an avionics shop fix the problem for a few hours of labor - they cleaned out the indicator and made sure it was not "catching" on anything.  Works fine now. 

 

Until I was able to get it fixed, I limited my flights to VOR/ILS approaches only in IFR conditions as I could hand fly using the my #2 radio for the approach or watch the approach on the #2 indicator as the AP flew it ready to disengage and fly myself.  I had it fixed in about a week.

 

What HSI are you using?  Mine was a King.

 

-Seth

[mooniac15u]

When you power up the 650 one of the self-test pages will include a test signal to your HSI.  The details of what you should see on your HSI should display on the screen.  I believe it should hide both flags and the needles should go to half deflection.  If the HSI doesn’t match the screen then there is likely a communications problem between the units.

[N601RX]

If the glide slope flag comes up and works correctly when doing a gps approach then the indicator and wiring is fine.  It's most likely a antenna/coax problem or a problem with the diplexers that splits the localizer and glideslope signal.  Does the localizer work? If so that rules out the antenna and coax up the the diplexer.

[jlunseth]

Its possible that the glideslope was just out on the ILS.  That is why the localizer approach is always published.  I have run into that a couple of times in real life, that is, there is a localizer signal and it is possible to capture the localizer, but no glideslope.  Have to quickly switch your thinking to the loc approach, which has a different minimum and you are on your own as far as descent rate.  I have also had the GS just not come in on my 430AW.  It has happened twice on scores of approaches with no good apparent reason.  On one occasion we had to go around because we did not catch it fast enough to convert to the loc appch, and on the second try the GS was there.  Don't ask me why.

 

I do always check the HSI during when the test screen comes up at startup of the 430. 

 

Do you have a backup nav radio and CDI in your aircraft?  After the couple episodes of no GS, I always set my second nav radio and CDI for the approach also, so I can use that if the GS does not come in on the GPS VLOC.

[MHemperly]

Is your nav data up to date?

[Will W]

First, did you check notams? I'm guessing you isolated that it wasn't that it was notated out of service. Did you report it to the tower/approach so they could get a second opinion?

This is common on mooneys. Essentially what happens is your nav antenna is on the tail. What you can do to help is have approach flaps and give yourself a reduced angle of attack. See, your wing with block the tail antenna and you won't receive any signal. This is very common on long body Mooney's and A36 Bonanza's.

When you're innersepting the localizer, have that be your time in your profile to deploy flaps. Then what happens is you might see it come off and on so in that case throw the gear and add full flaps. I guarantee you'll see it then.

If you're ever flying and it won't come in, nudge it in a dive a little. A little bit of pitch change will do a lot in this case.

[MHemperly]

From what I understand about the GTN stuff is the glide slope is locked out if the nav database isn't up to date.

There goes garmin gettin' us again

Mike

[Houman]

Is your nav data up to date?

Actually not all of it, not my terrain and some of the other items, but the actual nav data was updated last month..

I'm unfortunetly at an airport without any instrument approach, so I can't even test the radio part, starting my IFR training, it is difficult to know if it's me or the plane, and my 2 CFI's are not familiar with my airplane, only with school C 172 planes...

[chrisk]

The only thing that comes to mind is you may be displaying the GPS data and not the "NAV" data.  Without looking at the buttons, I think it is the CDI button that selects the source.   You may also want to play with the GTN 650 simulator.  It's a good way to figure out how it works.

[Marauder]

There have been a bunch of good suggestions. I would try to find an LPV approach and see what that does. It will prove the HSI hardware is working. Alternatively, if you can switch between Nav 1 and 2, I would try the second Nav.

As for the 650, on an ILS there is a specific capture zone for the conversion to the VLOC mode. Considering you are getting the signal for the localizer and can see the VLOC, that shouldn't be the issue.

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[PTK]

From what I understand about the GTN stuff is the glide slope is locked out if the nav database isn't up to date.

There goes garmin gettin' us again

Mike

This is incorrect.

You can fly full precision approaches, ILS or LPV, all day long with expired NAV data. Not legal IFR of course, but VFR only. The box doesn't know it contains old data until it's updated. What it will do is it will downgrade the approach from an LPV to a non-precision (LNAV) if it determines it doesn't have enough satellites for the precision approach.

After six months of expiration the approach plates only are not available. But the NAV data, even old, is available and usable VFR only.

Keep in mind the approach plates are nothing more than a pictorial representation of the approach. They don't drive the approach. What drives the approach are the waypoints in the NAV data no matter its age, which is in the box. It's up to the pilot to determine the status of his data.

As for the op not seeing GS on an ILS it has nothing to do with the NAV data. If he is in VLOC and verifying localizer it's probably something with GS signal and/or not being in position to capture it. If these are not the problem it's probably something with the HSI.

[jlunseth]

Technical distinction, but you can actually fly an ILS or LPV even if you have not updated your data, provided you are able to, and do actually, verify that there have been no changes to the plate and that the version you have is the current version.  Its been so long since I tried that, that I don't remember where to get the info on what the current plate is, but there is a list, probably on the FAA website, and it will state what plate amendment is the current one.

 

Much better just to change the data every 28 days and not have to worry about it.

[mike_elliott]

As for the op not seeing GS on an ILS it has nothing to do with the NAV data. If he is in VLOC and verifying localizer it's probably something with GS signal and/or not being in position to capture it. If these are not the problem it's probably something with the HSI.

  or something wrong with (lord forbid) the Garmin

[Marauder]

or something wrong with (lord forbid) the Garmin

Never! Blasphemy!!

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[PTK]

Never! Blasphemy!!

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There's a very special place in PES for those sacreligious ungodly types.

Purgatory Extended Stay!

[Marauder]

There's a very special place in PES for those sacreligious ungodly types.

Purgatory Extended Stay!

Personally, just fry my bacon... Just for the evil thoughts about Garmin.

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[mike_elliott]

Personally, just fry my bacon... Just for the evil thoughts about Garmin.

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I have sent countless dollars to money heaven with Garmin (and to be fair,  PS engineering, but I understand now they are not the standard), so my purgatory time should be short.

[MHemperly]

This is incorrect.

You can fly full precision approaches, ILS or LPV, all day long with expired NAV data. Not legal IFR of course, but VFR only. The box doesn't know it contains old data until it's updated. What it will do is it will downgrade the approach from an LPV to a non-precision (LNAV) if it determines it doesn't have enough satellites for the precision approach.

After six months of expiration the approach plates only are not available. But the NAV data, even old, is available and usable VFR only.

Keep in mind the approach plates are nothing more than a pictorial representation of the approach. They don't drive the approach. What drives the approach are the waypoints in the NAV data no matter its age, which is in the box. It's up to the pilot to determine the status of his data.

As for the op not seeing GS on an ILS it has nothing to do with the NAV data. If he is in VLOC and verifying localizer it's probably something with GS signal and/or not being in position to capture it. If these are not the problem it's probably something with the HSI.

Hmm that's strange because I just talked to my IA about this topic today and he says that his gtn stack locks out the glide slope if nav data is out of date. He has a 750/650 stack with a g500. I don't know maybe I misunderstood him. I personally don't have gtn I'm still rockin my 430waas.

Best of luck though

[Marauder]

I will settle the Nav database question when I pick up my plane next week. The last cycle expired on the 30th while my plane has been in the shop for her annual. Since I will be only flying VFR I pick her up, I will keep the old database in the unit and see if I can do a practice ILS approach into a nearby airport.

Anyone want to bet some Cheap Bast$&d bucks on the outcome?

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[Houman]

Well I noticed my nav Database on the 650 had expired at the end of April, so I guess it still could the NAV update as well.

 

Will check it next time I go flying !!!

[JaredDavis]

<snip>The box doesn't know it contains old data until it's updated. <snip>

 

 

That is very interesting. What is it based on?  I thought the data has an expiration date: "Valid till x". The box does talk to atomic clocks, so it knows the current date and time.