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Potential RNAV approach issue with IFD540
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vas4avidyne View Drop Down
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    Posted: 06 Nov 2022 at 1:16am
Let me start off by saying that I don't know if the 10.3 upgrade has anything to do with the issue I ran into today but I am wondering if that is a possibility. 

This relates to the RNAV Rwy 32 approach into KSTS (which has both LPV and LNAV minimums).

I have previously done the LPV approach there (when my IFD was running 10.2) - the IF/IAF is LUSEE and the crossing altitude is 3000. It looks like I was at about 3200 ft a couple of NM outside LUSEE when I was vectored on the the final approach course. The GS came in as expected and I was able to have the AP fly the LPV approach successfully.

In IMC today, I was cleared for the same approach (my first time doing this approach after the 10.3 upgrade). I was vectored onto the course a bit outside LUSEE and crossed LUSEE at 4200 ft (per ATC instructions). I then received a message indicating that the LPV approach was not available and that only the LNAV minimums were available. Unfortunately, the airport was reporting 300 broken so the ceiling was below the LNAV minimum (448 AGL). I tried switching to the ILS approach but I was way above the glide slope and landed up having to do a missed approach and then come back (after a few circuits in the MA Hold since it was busy) and then shooting the ILS approach.

I asked the controller if other folks had encountered the issue I ran into with the LPV but no one said anything.

A few questions:

- I checked my WAAS status before I took off and everything was fine. What could cause an LPV approach to become unavailable?
- is it possible that the error was caused by the fact that I was well above the glide path for the LPV as a result of which the IFD "downgraded" the approach to an LNAV?
- is it possible that this is a potential 10.3 issue?

Thanks,

Vas
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Dallas90 View Drop Down
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I had this same fault repeatedly (always in VFR) under 10.3. Never had it prior. I've only flown it once since I went back to 10.2, so I haven't had a chance to check it but I'll report back when I do.
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I'm going to have tech support contact you.  They'll give you instructions on how to send logs.  I'll look into it.
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@AviSteve, thanks (if that was for me). How long are logs maintained? I did one other flight after the flight where I had the LPV issue.

Vas
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Points: 2296 		Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSteve Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2022 at 6:19pm
Originally posted by vas4avidyne vas4avidyne wrote:

@AviSteve, thanks (if that was for me). How long are logs maintained? I did one other flight after the flight where I had the LPV issue.

Vas
Logs go back quite a ways, so it will be in there.


Edited by AviSteve - 08 Nov 2022 at 8:48am
Steve Lindsley
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n144sh View Drop Down
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I also have seen this with 10.3 on an approach I have done many times with 10.2.6 with no issues.   Two other WAAS GPS receivers in aircraft had no hiccups.
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I did a short test flight yesterday to test this and one other problem I had while using 10.3, now that I'm back to 10.2 both problems are gone.
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OK, I've now seen two separate units with this issue and IMHO this is serious.  Losing GPS integrity in the middle of an approach is not OK.

The first IFD540 I experienced this with was the one in my plane which is about a year old.  Never had a problem until upgraded to 10.3.

This morning it occurred on another IFD540, this one a new install, upgraded on the bench to 10.3.   
Here is what happened:
RNAV (LPV) approach into KCOE rwy 6.  
Crossing the IAF (POBIY) and making the turn, IFD alerted GPS Integrity lost - Dead reckoning.
I immediately switched to the AUX/GPS status page to check - all satellites were shown with no signal.
I was still above the clouds at this point and continued, monitoring the GPS signal page before descending for the approach.   The IFD did reacquire GPS pretty quickly - but reverted to LNAV +V rather than LPV.   I was able to successfully complete the approach.

Meanwhile, the Dynon WAAS GPS was rock solid throughout.

This is a really serious issue - losing GPS integrity in the middle of an approach pretty much negates the whole benefit of having the IFR navigator.   Avidyne - please address this urgently.    Meanwhile I now have to travel back to KCOE to downgrade this customers unit to 10.2.6.1 to have it functional/reliable.
 
Really not happy.
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@AviSteve, I have also had this same "LPV lost, downgrade to L/VNav" error since upgrading to 10.3 and not before.

As I am chasing a screen refresh lag issue and was recently advised by support (always very helpful) that the yahoos who installed the 2 WAAS antennae for the L3 Txpdr and the IFD540 put them right next to each other instead of the required more than 6 inches apart, I assumed this integrity loss was related to sporadic interference between the GPS antennae, because of proximity. 

Now I'm not.  Thanks for posting this issue, @vas4Avidyne, @n144sh, @Dallas90.

After submitting logs to support, support reported no identifiable problems and said that "10.3 did not update GPS functionality."

As another pleasant aside, I was toodling along VFR last week when the 540 alarmed a red terrain warning.  Much to my surprise, the box showed my ownship plowing into the ridge a mile to my right.

I'm getting the antenna moved and rolling back to 10.2.6


Edited by C88atapult - 20 Nov 2022 at 5:30pm
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I submitted my logs from the issue and this is the finding from when I lost GPS integrity on an RNAV approach:

"At this specific time, it appears that the IFD was trying to overwrite information from the previous RAIM request transmissions, but the reply was still coded as if it were in 10.2.6.1, but since the IFD was running 10.3 at this time it looks like the GPS could not process it so it initiated a restart of just that board in particular. This was probably resolved when you reverted to 10.2.6.1, if you advance to 10.3 again, usually problems that are "out of the ordinary" behavior for the IFDs can be resolved by rerunning the software. Since these are big changes between each operating system it is possible that some parts of it are missed and need to be reloaded again."

Note that the update to 10.3 followed the service bulletin precisely and passed the checksum verification.   My additional question to tech support why the 10.3 update passed the verification if there were remnant pieces of old code around was answered thusly:

"Although the checksums have all passed, there is a possibility that individual parts of the code have not taken, the checksums only make sure that the revision numbers have been changed which is part of the code, but since the update is so large it can miss small parts of it, but the checksums will still show themselves as conforming. "

You can draw your own conclusions, but mine is that a field update to 10.3 is not a robust process and you cannot be assured performance integrity even though the verification steps and checksums pass.   Presumably if the unit were returned and completely wiped and 10.3 loaded this might not occur.  For me this is unacceptable and I have returned to 10.2.6.1 to have some confidence in the system again.
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Points: 43 		Post Options Post Options   Thanks (0) Thanks(0)   Quote C88atapult Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 2022 at 7:29pm
@n144sh, that is odd that a RAIM request transmission (or an overwrite thereof) could have anything to do with an LPV approach, which can only be offered if WAAS is up and running.

A non-WAAS transmission issue causing a WAAS integrity issue seems weird, but my software experience is limited to database programming and my electrical engineering experience is nil.  But, with 30 years in tech I can translate support's response to you: "there are bugs, including in our checksum algorithms."

By any chance is there another GPS antenna near your Avidyne's?  Including a Stratus/Stratux inside on the cockpit roof?  Support (and an avionics tech) said distance (6 inches for other FAA approved antennas, 18 inches for non - TSO'd devices) are the minima for clear reception and lack of interference.




Edited by C88atapult - 20 Nov 2022 at 7:31pm
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There are no antennas that violate the spacing requirements and there have been no issues with 10.2.6.1   I don't know why the system does a RAIM request for the RNAV approach, but it did and it is right there in the logs that it rebooted.

I'm pretty decent with electrical stuff, EE degree and retired after 35 years in the semiconductor industry with HW, SW & management experience.   I do avionics installations now and have seen this same behavior on two separate aircraft after updating 10.2.6.1 to 10.3.   It is not an antenna issue. 
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Below is an excerpt of the logs showing the issue.   If you find the GPS approach you were flying using the date & time in the GPS log it would be interesting to see if there is similar behavior.

















597286462022100116:35:28GPSF_INFORAIM Request 0Valid Xmitlat:0.772969lon:-2.110199ETA Date:10/01/2022 Time:16:35:57





597297032022100116:35:29GPSF_INFORAIM Request 1Valid Xmitlat:0.772969lon:-2.110199ETA Date:10/01/2022 Time:16:50:57





597307592022100116:35:30GPSF_INFORAIM Request 2Valid Xmitlat:0.772969lon:-2.110199ETA Date:10/01/2022 Time:17:05:57





597678472022100116:36:07AlertsF_WARN  Lev:1 Cmd:0 Pri:008/000 Rpt:01 Own:00 Sent:00 IssueTm:59767 Dur:0 AD:0 ID:          GpsInt sMsg:<GPS Integrity Lost> lMsg:<GPS Integrity Lost Crosscheck Nav>
597679132022100116:36:07AlertsINFO  Lev:4 Cmd:0 Pri:013/000 Rpt:01 Own:00 Sent:00 IssueTm:59767 Dur:0 AD:0 ID:          Annun1 sMsg:<> lMsg:<>



597689032022100116:36:08CbitERRORNode Gps1 Timeout










597696292022100116:36:09AlertsF_ERROR  Lev:0 Cmd:2 Pri:008/000 Rpt:01 Own:00 Sent:00 IssueTm:59769 Dur:0 AD:0 ID:          GpsInt sMsg:<> lMsg:<>



597696292022100116:36:09AlertsF_WARN  Lev:1 Cmd:0 Pri:008/000 Rpt:01 Own:00 Sent:00 IssueTm:59769 Dur:0 AD:0 ID:           GpsFt sMsg:<GPS Fault> lMsg:<GPS Fault>


597696292022100116:36:09AlertsF_INFO  Lev:2 Cmd:0 Pri:008/000 Rpt:01 Own:00 Sent:00 IssueTm:59769 Dur:0 AD:0 ID:          DedRek sMsg:<Dead Reckoning> lMsg:<Position updated using dead reckoning>
597696292022100116:36:09SynVisF_INFOInhibit Reason Changed from 0x00 to 0x80 








597696952022100116:36:09AlertsF_INFO  Lev:2 Cmd:0 Pri:000/010 Rpt:01 Own:00 Sent:00 IssueTm:59769 Dur:0 AD:0 ID:     FLTAInhibit sMsg:<FLTAUnavailable> lMsg:<Invalid GPS Position/Velocity>
597746512022100116:36:14FmsINFOVNAV state changed to UnableVnav









597835552022100116:36:23CbitINFONode StatusGps1150x80 POSTFailed
120x0
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Fantastic!  Thanks!  
Now I just need to find the USB drive with the data...
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I'm sorry to be so blunt - this is a ridiculous or terrifying explanation depending on whether it turns out to be false (incorrect explanation) or true (that this in fact could happen during an upgrade). 

AviSteve, would you please check with your Engineering team if the possibility of an upgrade having only partially "taken" is real despite correct checksums. Also, I haven't heard back from Tech Support about the status of the ticket I opened on the RNAV approach issue (#IPS00091532).

So far, I have hung in there with 10.3 despite all the issues but I am now starting to seriously consider switching back to 10.2.6.....

Thanks,

Vas

Originally posted by n144sh n144sh wrote:

I submitted my logs from the issue and this is the finding from when I lost GPS integrity on an RNAV approach:

"At this specific time, it appears that the IFD was trying to overwrite information from the previous RAIM request transmissions, but the reply was still coded as if it were in 10.2.6.1, but since the IFD was running 10.3 at this time it looks like the GPS could not process it so it initiated a restart of just that board in particular. This was probably resolved when you reverted to 10.2.6.1, if you advance to 10.3 again, usually problems that are "out of the ordinary" behavior for the IFDs can be resolved by rerunning the software. Since these are big changes between each operating system it is possible that some parts of it are missed and need to be reloaded again."

Note that the update to 10.3 followed the service bulletin precisely and passed the checksum verification.   My additional question to tech support why the 10.3 update passed the verification if there were remnant pieces of old code around was answered thusly:

"Although the checksums have all passed, there is a possibility that individual parts of the code have not taken, the checksums only make sure that the revision numbers have been changed which is part of the code, but since the update is so large it can miss small parts of it, but the checksums will still show themselves as conforming. "

You can draw your own conclusions, but mine is that a field update to 10.3 is not a robust process and you cannot be assured performance integrity even though the verification steps and checksums pass.   Presumably if the unit were returned and completely wiped and 10.3 loaded this might not occur.  For me this is unacceptable and I have returned to 10.2.6.1 to have some confidence in the system again.
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Points: 558 		Post Options Post Options   Thanks (0) Thanks(0)   Quote paulr Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 2022 at 7:36am
That reply sounds to me like a support rep who got too far out over his skis and interpolated across gaps in his knowledge. I would faint dead away if it turns out that there is no effective checksum/CRC mechanism for checking code integrity and patch completeness in the IFDs, as this reply implies.

On the other hand, at least Avidyne won't kill me with a pitch trim runaway in my autopilot, so there's that.
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If the checksums (actually CRCs) are as expected, then the software was correctly loaded.  There is no "partially taken".  I suppose there could be a flash memory failure during the update, but in that case the CRCs would not match.

I'll talk with the tech support team and see what the source of that response was.  I'm sure there was some nugget of information that was extrapolated into that explanation which was, at best, poorly worded.
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FYI, we are actively trying to figure this one out, but not everyone with 10.3 is experiencing this.  We're  looking at the possibility that older hardware is working intermittently with the 10.3 GPS software.

So, if you've had this issue, can you send me a PM with the serial number of your IFD(s)?  @Dallas90, I know you went back to 10.2.6, but it would still be useful to have that information from you too.
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Thanks AviSteve - sent a PM with the two S/N's I have personally seen affected with this issue.
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Also sent a PM with our S/N for this issue.

Thanks.
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