Loss of position information in flight

[GarethHorne]

Any idea what's happening here? Took my PilotAware on a flight from Netherthorpe to Duxford today and lost position shortly after take off. However SkyDemon was still reporting 11 satellites, as was the webpage when I logged onto the PilotAware homepage.

Tried disconnecting and reconnecting the wifi and restarting SkyDemon multiple times with no effect. The only thing I did not do was reboot the PilotAware box (which I wish I'd thought to try whilst airborne!)

When I changed from Flarm to internal navigation SkyDemon performed normally for the remainder of the flight.

Interestingly on the return trip the PilotAware / SkyDemon setup performed flawlessly, no changes to its position in the aircraft, power supply or handset.

Any thoughts?

Thanks Gareth

[Admin]

Hi Gareth,

Well that is one of the strangest I have ever seen
Clearly the home page is still reporting that:
- Still connected to 1 NAV device
- Received 2275 GPS Messages and has 11 satellites

I think I need to consider what additional debug I could add to see what has gone awry.
I know it is too late now, but a couple of snapshots of the Traffic page would have been useful because at the top is shows the Lat/Long as reported from the GPS.
so a couple of snapshots a few seconds apart should show a new location

Finally, to see the messages being sent to the NAV device you can tick the NAV checkbox on the configure page, save, then look at the logging page.
This would show everything sent to the NAV device.

Unfortunately - its difficult to do this whilst flying isn't it.

I will consider what additional info can be reported on the home page, and what additional info can be collected to be analysed offline.
I am starting to add Status/Debug information into the .trk files which are created in-flight.

Sorry to hear of the trouble, but glad to hear it was OK on the return - hopefully a glitch we can identify.

BTW, which type of GPS receiver is this, is it the Dongle or Mouse ?

Edit: Actually, you should have a .trk file for this part of the flight - can you let me have a copy ? you can download from the 'ListTrack' page. This will at least give us the NMEA messages sent to the NAV device.

Thx
Lee

[peastlake]

I've not got any screen prints - but I had this at the weekend too. "Seeking GPS Satellites" reported on SkyDemon- but with a number of "found" underneath.

It was okay before the last update, AFAIK!

[Admin]

I've not got any screen prints - but I had this at the weekend too. "Seeking GPS Satellites" reported on SkyDemon- but with a number of "found" underneath.

It was okay before the last update, AFAIK!

But you will still have the track file if you can provide that.
Did you need a reboot to resolve this, or did it resolve itself ?

Thx
Lee

[Admin]

One thing that could be happening here (but this is not a recent change)
is that some NMEA messages are invalidating others.

At the moment I collect the following NMEA messages
GPGGA
GPGLL
GPGSA
GPRMC
GPZDA
GPVTG

Each of these messages have individual status about their quality.
At the moment if any of these are reported as INVALID, then I decide that they are all INVALID
This is probably an overkill, and could be relaxed to say that validity of each individual message
should NOT be constrained by each other.

In fact I suspect the GPGLL message could possibly be at fault here, I do rarely see that message
reported as INVALID but if that is the case, this should not invalidate the GPGGA, unless the GPGGA
itself is reported as INVALID

This could be related to what is described here.

Thx
Lee

[GarethHorne]

Thanks for the the info Lee, will download the .trk files tonight when I get home and pass them on. The GPS is the dongle plugged directly into the PilotAware, I do have a 30cm extension, but it wasn't in use on this occasion.

 I've never had any issues using the GPS dongle directly connected in the past in the aeroplane, it's sometimes useful to put the dongle on an extension at home when using it as a base station in the window to get a GPS lock.

[GarethHorne]

Hello Lee, here are the track files from yesterday, hopefully you can identify the relevant  one

https://www.dropbox.com/s/7ckf4ffcpzpie34/2016-07-25%20PilotAware%20tracks.zip?dl=0

thanks

Gareth

[Admin]

Hi Gareth

Yes here it is, just as the GPS stops

Code: [Select]

$GPGGA,121812,5310.927,N,00101.809,W,2,05,1.0,925.4,M,-34.0,M,,*74
$GPGSA,A,3,20,02,10,13,04,08,07,23,,,,,1.00,1.00,1.00*0A
$GPRMC,121812,A,5310.927,N,00101.809,W,106.000,137,250716,,,A*7A
$GPGGA,121813,,,,,1,11,,,,,*6F
$GPGSA,M,1,,,,,,,,,,,,,,,*12
$GPRMC,121813,V,,,,,,,,A*54
$GPGGA,121814,,,,,1,11,,,,,*68
Unfortunately, what this does not tell us - is why.
So I need to capture some more information in the tracking, so if we see this again we can reverse diagnose
the cause.

one thing I did notice, is that there were restarts at the following times

Code: [Select]

2016-07-25_11-39.trk // 12:39
2016-07-25_12-05.trk // 13:05
2016-07-25_12-10.trk // 13:10
2016-07-25_12-13.trk // 13:13
Does this sound correct ?
Were you rebooting at these times, because if not it would indicate a power issue, possibly causing reboots

Thx
Lee

[GarethHorne]

The first restart was definitely deliberate Lee, that would be before we left Netherthorpe, whilst setting it up in the aeroplane. The next 3, no don't recall selecting reboot from the homepage although I was switching WiFi on and off, closing and reopening SkyDemon to try and get it working and may have had finger trouble! I'd got the PilotAware set up behind the seats under the canopy in the Eurostar so I couldn't physically reach it to power it on and off manually.

I was in the right hand seat by the way, if I'd been flying I'd have simply switched to internal gps it until back on the ground. I've not had issues with that power pack before (been using it since last Autumn) and it still had plenty of juice for the flight home without problems. I do have another power pack I can try to see if that makes a difference next time I fly.

Thanks Gareth

[Paul_Sengupta]

I had this too, weekend just gone. I can't remember on which flight though to get the track logs, but I power reset the PAW and all was well.

[Admin]

Hi Paul

I thought I posted something on this, but must have sent a personal email.
I tracked down a potential bug where I was being too pessimistic in decoding the GPS/NMEA.

As I am sure you are aware, there are a number of messages I decode, such as
GPGGA
GPGSA
GPRMC
GPVTG
(cannot recall all the others)

Some of these sentences have a status or quality indicator. in the 20160708 release and prior,
if I decode any of these messages which have a status=invalid or quality=2D (rather than 3D).
I pessimistically decide ALL messages are invalid - this is wrong, and the status should be
applied individually to each message. It is then incumbent on the Navigation device to decide the
overall quality/status of the NMEA sentences rather than PilotAware trying to filter the messages
early in the process.

This relaxation will be in the next release.

Thx
Lee

[Paul_Sengupta]

You said it a few messages further up this thread... 

[exfirepro]

You're obviously working too hard, Lee 

Peter