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Why won't my AP fly this approach????

A

amekler

Well Known Member
Patron
I have an RV 10 with AFS4500/Vizion AP/Avidyne 440
I have no problems flying other LPV approachs on AP but at KIZG RNAV 32 LPV my AP shows FLG the minute the approach becomes active.
I still get a GS indication and can disconnect and hand fly the approach
Any thoughts?

Alan
N668G
 

Attachments

  • FlightAware_IZG_IAP_RNAV (GPS) RWY 32.pdf
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The most common failure I see on approaches like this is that the pilot (and/or autopilot configuration) expects to see a glide slope at SERPA and ANDRU. But they’re step down fixes. You won’t get a GS until some point before the FAF, after ANDRU.
Edit added: If you are getting a glide slope indication at SERPA it’s an ‘advisory’ indication generated by the 440, not a real GS. Look at the actual numbers on the chart. The descent from SERPA to ANDRU is very shallow, much less than 3 deg (stupid FAA charting does not make this obvious. Look at a Jepp chart). I don’t know how your autopilot handles these advisory glide slopes (apparently not well). Try it again, force the AP to do step downs at these fixes, then arm the GS.
 
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bob,
yes I let the autopilot fly the approach and don't get a glide slope at Serpa or at andru. I pass andru and descend to 2200 feet. I'm level at 2200 feet and then get the glide slope on my pfd but the autopilot goes right to FLG never ARM and the plane levels off at 2200 until I disengage the autopilot and then can hand fly it.
I've tried reengaging the autopilot but it always goes to FLG
Alan
cell 603-493-9441 if you have time to discuss
 
Okay. With my limited knowledge of the equipment you’re using I can’t think of anything else - especially if it behaves on other approaches!
 
of interest before I had the avidyne 440 I had a Garmin 430W and had the same issue
A friend of mine with another RV-10/Sorcerer AP/ Garmin 650 and AFS 5400T also has this issue
I checked with the FAA and they see no errors in their codes for this approach
Alan
 
Alan,

On the surface, it sounds like some kind of autopilot incompatibility with your navigator, but it could be something else.

You didn't say, but it sounds like you are flying this RNAV approach with the SERPA transition, not vectors-to-final.

When flying this approach with the transition, the glidepath (GP) guidance should come alive as you cross the FAF-1 waypoint (ANDRU). Are you seeing this happen on the PFD display at ANDRU?

Something else you might try as a test on this approach is to activate the approach with the SERPA transition and fly the procedure turn. As you fly inbound on the final approach course at 3,600 ft outside of the SERPA IAF, activate vectors-to-final. The glidepath (GP) guidance should come available immediately with the glidepath (GP) shown above the aircraft. Does it? If so, does the autopilot see and like this vertical guidance?

The glidepath (GP) is at about 5,200 ft at SERPA, so you are well under the glidepath when inbound at 3,600 ft. With my GNX 375 and G3X Touch system, I can activate vectors-to-final on this approach outside SERPA at 3,600 ft, stay in altitude hold at 3,600 ft, and automatically intercept/capture the glidepath (GP) with the autopilot between SERPA and ANDRU and fly it in. No manual descent required.

Of course, I can also fly the approach with the SERPA transition, descend to 3.100 ft between SERPA and ANDRU, and capture the glidepath (GP) shortly after ANDRU (with no further manual descent). Note that the glidepath (GP) is close to 3,200 ft at ANDRU, so if you are much above your 3,100 ft target altitude, you could overfly the glidepath and miss the capture.

KIZGRNAV32.png

Steve
 
Steve,
I fly the full approach not VTF. at Serpa descend to 3100 . at andru I descend to 2200 and get the GS FLG on the ap between andru and hirmn. the gs shows on my pfd.
I have tried staying at 3600 thinking the gs will show but it doesn't show til almost at hirmn.
on other lpv approaches I get a glide slope indication at the IAF and the AP goes to GS ARM then CPL.but not on this approach.
Alan
 
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It almost sounds as if commanding the AP to do a descent/level off at a new altitude is dropping it out of "approach armed" mode. Can you check that after reaching 2200' the AP is still armed for the approach?
As Alan suggested, switching to a "vectors to final" mode as you approach SERPA should make this approach look just like the ones where it works - just continue inbound at 3600' until GS intercept. But it really should work as published, too.
 
amekler said:
I have an RV 10 with AFS4500/Vizion AP/Avidyne 440
I have no problems flying other LPV approachs on AP but at KIZG RNAV 32 LPV my AP shows FLG the minute the approach becomes active.
I still get a GS indication and can disconnect and hand fly the approach
Any thoughts?

Alan
N668G
Click to expand...

Alan,
Is the 440 connected to the A/P through the EFIS? Does the EFIS interpret/massage the data from the 440 prior to sending it to the A/P? Do you have a switch to send the data directly from the 440 to the A/P?
 
Skid,
Yes I fly the AP through the EFIS. Normally the GS comes up before I need to descend and the AP captures it but on this approach no GS until I'm almost at the final approach fix.
I tried switching to have the AP take commands directly from the 440 and the AP never arms and reads FLG.
Of note a friend with a Sorcerer AP/AFS 5400/and Garmin 650 also behaves the same way

Alan
 
amekler said:
Skid,
Yes I fly the AP through the EFIS. Normally the GS comes up before I need to descend and the AP captures it but on this approach no GS until I'm almost at the final approach fix.
I tried switching to have the AP take commands directly from the 440 and the AP never arms and reads FLG.
Of note a friend with a Sorcerer AP/AFS 5400/and Garmin 650 also behaves the same way

Alan
Click to expand...

Alan,
I would contact Avidyne, if you haven’t already, regarding the issue. They may have some insight, also contact TruTrak/Bendix, if you haven’t already, to get their input. Based on your friend having the same issue. It would also be interesting to hear what Garmin has to say since your friend is having the same issue.
 
Alan,

I would call AFS.

When the EFIS/GPS autopilot switch is in the EFIS position, ALL ARINC 429 data coming to the Vizion autopilot is from the EFIS, not the GNS 430W, GTN 6XX/7XX, or 440.

You know the data coming from the IFR navigator is good, because you see good glidepath vertical deviation data on the PFD. The EFIS supplied ARINC 429 data is not keeping the autopilot happy for this approach.

As shown in the Vizion manual, the autopilot is receiving a flagged vertical steering signal from the EFIS when it sounds like it should not.

VizionVerticalFlag.png

Steve
 
My EFIS is a GRT

I know little/nothing about the AFS gear, but do you need to manually "ARM" and "EXECUTE" the approach? One button push.
Terry, CFI
RV9A N323TP
 
Longez said:
Alan,

I would call AFS.

When the EFIS/GPS autopilot switch is in the EFIS position, ALL ARINC 429 data coming to the Vizion autopilot is from the EFIS, not the GNS 430W, GTN 6XX/7XX, or 440.

You know the data coming from the IFR navigator is good, because you see good glidepath vertical deviation data on the PFD. The EFIS supplied ARINC 429 data is not keeping the autopilot happy for this approach.

As shown in the Vizion manual, the autopilot is receiving a flagged vertical steering signal from the EFIS when it sounds like it should not.

View attachment 23885

Steve
Click to expand...


I think the issue is I don't get a gs indication til late in the approach.
on other approaches the gs arms much earlier.
 
terrykohler said:
I know little/nothing about the AFS gear, but do you need to manually "ARM" and "EXECUTE" the approach? One button push.
Terry, CFI
RV9A N323TP
Click to expand...

Terry
I activate the approach
put the EFIS in lat arm vertical arm mode and put the ap in GPSS VS mode
This is the only approach where I get the AP not to arm
Alan
 
amekler said:
I think the issue is I don't get a gs indication til late in the approach.
on other approaches the gs arms much earlier.
Click to expand...

Alan,

You will receive the vertical glidepath deviation guidance from the navigator immediately upon crossing the FAF-1 waypoint (ANDRU). You should not be receiving vertical glidepath guidance until crossing ANDRU (unless you activate vectors-to-final).

This approach is no different from other RNAV approaches except that in many RNAV approaches, there are no additional waypoints in front of the FAF-1 waypoint (which is often the IAF waypoint).

Are you not getting vertical glidepath guidance on your PFD immediately as you cross over ANDRU?

Steve
 
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Steve,
yes I get the GS crossing andru but the AP goes right to FLG
MY AP won't fly this approach. I have not tried VTF .
I can hand fly the approach .
Alan
 
amekler said:
I think the issue is I don't get a gs indication til late in the approach.
on other approaches the gs arms much earlier.
Click to expand...

As Steve said, this is less common but not totally uncommon. Out here in the mountain-filled west such approaches are more common.

I think you said that the AP behaves the same way when you switch it to get data directly from the 440, with the EFIS out of the loop? If this is so, then the issue is likely with the AP. e.g., after being told to execute a step down, it is dropping out of ‘approach armed’ mode.
Edit: I’m a bit confused by the nomenclature. On my (Trio Pro) AP, the pilot has to manually ‘arm’ the approach, e.g., tell the AP to ‘capture’ and ‘execute’ the upcoming approach. Are you saying your AP somehow self-arms? Maybe I just mis-read?
 
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amekler said:
Terry
I activate the approach
put the EFIS in lat arm vertical arm mode and put the ap in GPSS VS mode
This is the only approach where I get the AP not to arm
Alan
Click to expand...

Ignore my last edit. You must figure out how to get the autopilot armed. Perhaps, your AP won’t arm when there’s no GS data? Have you tried simply re-arming the AP as soon as you level at 2200’?
 
Bob,
No that I'll try next
the ap has to be in alt hold to arm
maybe its not in alt hold long enough
I hope I hear something back from Bendix-king(trutrac)
Alan
 
I have similar problem with trutrak efis ap/garmin 530w combo flying the RNAV 11 into KOCQ. If I arm the vertical mode to early or to late it doesn't capture. I have about a 5 second window to get it. I can fly the same approach in my Cardinal (Avidyne/ STEC) with no problems.

I realize this doesn't solve the problem, but at least it's confirmation you aren't crazy.
 
Okay, method of last resort: I read the manual. It seems to indicate (although not perfectly clear) that you need to be receiving the GS before the AP will accept the "arm" command.
 
Rallylancer122 said:
I have similar problem with trutrak efis ap/garmin 530w combo flying the RNAV 11 into KOCQ. If I arm the vertical mode to early or to late it doesn't capture. I have about a 5 second window to get it. I can fly the same approach in my Cardinal (Avidyne/ STEC) with no problems.

I realize this doesn't solve the problem, but at least it's confirmation you aren't crazy.
Click to expand...

yes I believe there is an issue in the TruTrak as it behaves the same with a garmin430w or avidyne 440. Also the TruTrak sorcerer/GTN650 in a friend's RV10 won't arm the arm the approach as well. The FAA has validated the approach data as well as Jeppensen.
Alan
 
I fly a TruTrak "Advanced Autopilot", which is a TT Digiflight 2 VSGV modified by TT, targeted to interface with the AF-4500. I had some problems getting the TT to couple with a local approach, and found some guidance in an old DigiFlight document regarding approach arming. Here's what I found worked for me:

- Must be in altitude hold mode on the AF4500, below the glide slope by one dot, for at least 7 seconds (per page 9 of the Digiflight 2 manual)
- Then AP will arm
- As VDI passes through center, AP will couple to GS.
 
DFII manual and screen shot attached.

FLG apparently means VDI is high right now. Expected sequence of events for DFII is FLG, HLD, ARM, CPLD.

A call to Advanced Flight Systems might shed some light on the OP's issue. Rob Hickman's customer service has been outstanding.
 

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  • Tru Trak DigiflightIIOperatingManual.pdf
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  • 2022-03-26 (2).png
    2022-03-26 (2).png
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Reading through this thread reminds me why I will only install panels/navigators from a single manufacturer, everything just works :)
Mixing and matching inevitably leads to problems somewhere.
 
Tim Lewis said:
DFII manual and screen shot attached.

FLG apparently means VDI is high right now. Expected sequence of events for DFII is FLG, HLD, ARM, CPLD.

A call to Advanced Flight Systems might shed some light on the OP's issue. Rob Hickman's customer service has been outstanding.
Click to expand...

yes I'm talking to Rob. This is the Vizion 385 AP. Its a bit different. When it goes to FLG the AP levels off. The GS will be below you and it will not dive and intercept
Alan
 
Walt said:
Reading through this thread reminds me why I will only install panels/navigators from a single manufacturer, everything just works :)
Mixing and matching inevitably leads to problems somewhere.
Click to expand...

Walt, I strenuously object. Mixing and matching requires someone to think and check for compatibility issues, but if properly done does not ‘inevitably lead to problems…’ I use a Garmin 420W, a GRT Hx, and Trio Pro AP, and they all work flawlessly together. I routinely shoot the RNAV 30 KTCY approach, which is just like the OP’s approach - several step downs before GS intercept. My system flys this flawlessly. So the OP’s issue is not due to mixing and matching.
 
BobTurner said:
Walt, I strenuously object. Mixing and matching requires someone to think and check for compatibility issues, but if properly done does not ‘inevitably lead to problems…’ I use a Garmin 420W, a GRT Hx, and Trio Pro AP, and they all work flawlessly together. I routinely shoot the RNAV 30 KTCY approach, which is just like the OP’s approach - several step downs before GS intercept. My system flys this flawlessly. So the OP’s issue is not due to mixing and matching.
Click to expand...
Love the movie, so I'm going to have to overrule your "strenuously objecting" to my statement. :D

But really, tell me exactly how does one go about checking for "compatibility issues" when purchasing equipment or during installation?
And who do you turn to when something doesn't work?
(pretty sure most vendors will say it the other guy's problem, been there/done that.)

Maybe I'm just getting lazy in my old age, I just like sh*t to work, and if it doesn't, I got one person to call to help me fix it.

Sorry for the thread drift, I know this doesn't help the OP with his issues.
 
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amekler said:
the vision AP needs to see the glide slope above you for 6 seconds before arming
Alan
Click to expand...

So by my back of the newspaper calculations, this approach has incredibly tight tolerances. In fact if your altimeter is at one end of the allowable error, or you’re 6 seconds slow on starting down, you won’t capture. Can you manually arm and capture once you’re level at 2200’?

Note to Walt: I understand your position. You build panels for a living, so ‘time is money’. For myself, building an EAB was for ‘my own enjoyment and education’, so ‘time was fun’!
 
amekler said:
the vision AP needs to see the glide slope above you for 6 seconds before arming
Alan
Click to expand...

Alan,

I watched your video frame-by-frame as you approached the FAF-1 waypoint (ANDRU) at 3,100 ft.

At the very first frame where the vertical deviation indicator (VDI) pops up showing the location of the glidepath, the glidepath is surprisingly close to the aircraft with only a second or two before you intercept the glidepath.

AFSVDI.png

When I fly this approach with my system in the same manner (crossing ANDRU at 3,100 ft), and watch the video frame-by-frame, the VDI pointer is much higher at the dot above the center when the VDI first pops up with quite a bit of additional time before glidepath interception.

G3XVDI.png

When flying at 3,100 ft, the glidepath is only 100 ft above ANDRU and the aircraft will intercept this glidepath in only 0.3 nm after crossing ANDRU, so this is indeed a very "tight" approach.

KIZGRNAV32.png

In contrast, for the similar appearing approach at Tracy airport that Bob mentions above, the glidepath is 470 ft above the FAF-1 waypoint (HELVA) and the aircraft doesn't intercept it for another 1.5 nm after crossing HELVA at 2,500 ft. No doubt that this approach would be no problem for your autopilot.

KTCY RNAV 30.png

Not sure why your VDI becomes active with so little vertical space between the aircraft and the glidepath at ANDRU, but this is certainly not working for an autopilot that requires 6 secs to arm.

Steve
 
BobTurner said:
So by my back of the newspaper calculations, this approach has incredibly tight tolerances. In fact if your altimeter is at one end of the allowable error, or you’re 6 seconds slow on starting down, you won’t capture. Can you manually arm and capture once you’re level at 2200’?

Note to Walt: I understand your position. You build panels for a living, so ‘time is money’. For myself, building an EAB was for ‘my own enjoyment and education’, so ‘time was fun’!
Click to expand...

I tried one approach descending at 700 feet a minute after crossing andru at 3100 -it worked but I repeated it and it didn't work????

Alan
 
Longez said:
Alan,

I watched your video frame-by-frame as you approached the FAF-1 waypoint (ANDRU) at 3,100 ft.

At the very first frame where the vertical deviation indicator (VDI) pops up showing the location of the glidepath, the glidepath is surprisingly close to the aircraft with only a second or two before you intercept the glidepath.

View attachment 24117

When I fly this approach with my system in the same manner (crossing ANDRU at 3,100 ft), and watch the video frame-by-frame, the VDI pointer is much higher at the dot above the center when the VDI first pops up with quite a bit of additional time before glidepath interception.
I I choose vtf at 3600 inbound from serpa it works

View attachment 24119

When flying at 3,100 ft, the glidepath is only 100 ft above ANDRU and the aircraft will intercept this glidepath in only 0.3 nm after crossing ANDRU, so this is indeed a very "tight" approach.

View attachment 24118

In contrast, for the similar appearing approach at Tracy airport that Bob mentions above, the glidepath is 470 ft above the FAF-1 waypoint (HELVA) and the aircraft doesn't intercept it for another 1.5 nm after crossing HELVA at 2,500 ft. No doubt that this approach would be no problem for your autopilot.

View attachment 24120

Not sure why your VDI becomes active with so little vertical space between the aircraft and the glidepath at ANDRU, but this is certainly not working for an autopilot that requires 6 secs to arm.

Steve
Click to expand...
Steve,
This is the only approach where it wouldn't work. A friend with a Garmin 650 and av TruTrak sorcerer AP, AFS 5400 also could not get the AP to arm the GS
Alan
 
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