PilotAware
British Forum => Technical Support => Topic started by: a.alexeev.p on April 20, 2023, 10:34:47 pm
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Hi all,
Recently was trying to watch some aircraft through PAW while on the ground and noticed a strange thing - couple aircraft that I know for sure had an ADS-B out CAP1391 devices on (and no Mode S transponder as one was actually parked) were showing up as bearingless. What could be the reason for it? I believe they were showing normal after take off…
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Hi all,
Recently was trying to watch some aircraft through PAW while on the ground and noticed a strange thing - couple aircraft that I know for sure had an ADS-B out CAP1391 devices on (and no Mode S transponder as one was actually parked) were showing up as bearingless. What could be the reason for it? I believe they were showing normal after take off…
Do you mean no mode S as not fitted, or no mode as not flying/in standby?
Does the CAP1391 have the setting for flying/not flying enabled? I think the default may be 10 knots to switch over? Been a while since I looked...
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So aircraft electrics completely off as somebody just forgot their CAP1391 device on in a parked aircraft. Not sure what their transmit settings are, but it was visible on a flight tracking app and clearly shown as ADSB as I would expect and it is just PAW that for some reason was treating it as bearingless
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Hi Alex,
What PAW software version was in use?
I seem to recall there was an issue where some DF18 devices (SkyEchos) were showing as DF17 (Transponders), but I can't recall whether this was due to a PAW or ATOM software fault. I'm pretty sure it was fixed at the time though.
Regards
Peter
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I don’t recall the exact version, but it was the latest one that was released in the past 1-2 months. Same behaviour on my old classic paw and my friend’s brand new rosetta. It is just the classic picked up one aircraft and rosetta another (both with SE2 left on).
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Do these aircraft also have mode S transponders?
Are you sure that the transponder is giving a bearingless, and cap1391 is not detected?
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Just to reconfirm:
Aircraft does have a mode s transponder only (not ADSB), but it is not very relevant because it was parked and completely off, just the pilot left their 1391 device on. I am sure of that also because on a flight tracking app I could see the exact position and clear marking that the signal was ADSB.
Two different PAW devices were nevertheless showing it as bearingless. When the the aircraft took off later - it started to show normally (although I can’t be 100% sure if when showing normally it was direct from the 1391 device or Mode S MLAT function of PAW). It was still showing as ADSB on the flight tracking app.
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A skyecho has a vso setting
Anything less than this and it will not emit a position report
Can you check its setting
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I can definitely try and ask, however, as a flight tracking app was definitely showing it’s position on the ground (definitely not MLAT) and clearly marking it as ADSB - then it is fair to assume it was transmitting?
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I can definitely try and ask, however, as a flight tracking app was definitely showing it’s position on the ground (definitely not MLAT) and clearly marking it as ADSB - then it is fair to assume it was transmitting?
Yes if it was not moving
Do you have the icao of the se2 devices, and date/time of flight?
Thx
Lee
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Thanks Lee! Yes sure:)
40632D around 14:30-15:00 UTC on 17th April 2023
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Edited
Alex,
That aircraft reports as a Cessna 172 out of Goodwood.
I don't of course have the full picture, but looking at PilotAware Replay and the PilotAware Database for the date in question, the aircraft was reporting what appears to be a very weak Mode S signal (via MLAT) around the south coast in the Goodwood / Selsey area from about 9:15am - initially operating what appear to be circuits out of Goodwood until about 09:30, but with pretty erratic position reporting. The weak MLAT reports on our network were to be fair probably partly attributable to the aircraft operating at very low level (less than 1000ft). It then appears again from about 10:30 to 11:30 - again as an extremely poor Mode-S (MLAT) signal, but with very occasional bursts of ADSB 18 - probably from a poorly sited CAP1391 device. It next appears from about 12:15 to 12:30 - again as a very irregular CAP1391 ADSB 18 Only signal between Goodwood, Selsey and Hayling Island, before suddenly switching from CAP1391 ADSB Only back to Mode-S again (as if the transponder was suddenly switched on) and thereafter showing a poor mix of ADSB / Mode-S MLAT back to Goodwood - again with extremely erratic position reporting (at low level) and lots of gaps. There is then a single 'ping' at 14:06 at 375ft (at Goodwood - presumably in the circuit or on the ground), followed by a re-appearance as a mixture of CAP1391 ADSB and MLAT in the Goodwood /Selsey/Bognor Regis area from 15:40 to 16:15, after which it seems to be operating as purely Mode-S at a fairly consistent altitude of between 750 and 950ft until it returns to Goodwood at around 16:50.
The erratic nature of the Mode-S reports would mean that PilotAware would keep changing between known-position (when the MLAT is reliable) and Bearingless (when it is not) and the aircraft would be reported as such on SkyDemon (provided you had 'Show Bearingless Targets' enabled). This would certainly explain (at least as far as I can tell from what you have sent us) what you were experiencing - i.e. intermittent known position reports from the poor MLAT/CAP1391 interspersed with random intermittent Bearingless target reports from the Mode-S - NOT the CAP1391.
It's certainly one of the most erratic reports I have ever looked at. If it was my aircraft I would be extremely concerned about the poor quality signals which appear to be being transmitted from it - with ADSB CAP1391 (perhaps understandably) only reporting out to less than 10Km, but my greater worry is the extremely poor quality of the MLAT reports which may well indicate a problem with the aircraft's Mode-S transponder.
Best Regards
Peter
p.s. you can check this for yourself at https://playback.pilotaware.com/playback/groundstations/ by selecting the Transmission Type, putting in the ICAO code and Start Time (3 hour segments max, though shorter periods give a more detailed expanded report) and clicking on 'Search'.
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Thanks Lee! Yes sure:)
40632D around 14:30-15:00 UTC on 17th April 2023
Take a look at this icao code using vector
https://www.pilotaware.com/analysis/vector
Be sure to disable ALL days except 17/4
You will notice the performance is not great, and this is base upon a 12db antenna on the ground stations. A 2db / 3db gain antenna airborne will be considerably worse
Thx
Lee
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Edited
Alex,
That aircraft reports as a Cessna 172 out of Goodwood.
I don't of course have the full picture, but looking at PilotAware Replay and the PilotAware Database for the date in question, the aircraft was reporting what appears to be a very weak Mode S signal (via MLAT) around the south coast in the Goodwood / Selsey area from about 9:15am - initially operating what appear to be circuits out of Goodwood until about 09:30, but with pretty erratic position reporting. The weak MLAT reports on our network were to be fair probably partly attributable to the aircraft operating at very low level (less than 1000ft). It then appears again from about 10:30 to 11:30 - again as an extremely poor Mode-S (MLAT) signal, but with very occasional bursts of ADSB 18 - probably from a poorly sited CAP1391 device. It next appears from about 12:15 to 12:30 - again as a very irregular CAP1391 ADSB 18 Only signal between Goodwood, Selsey and Hayling Island, before suddenly switching from CAP1391 ADSB Only back to Mode-S again (as if the transponder was suddenly switched on) and thereafter showing a poor mix of ADSB / Mode-S MLAT back to Goodwood - again with extremely erratic position reporting (at low level) and lots of gaps. There is then a single 'ping' at 14:06 at 375ft (at Goodwood - presumably in the circuit or on the ground), followed by a re-appearance as a mixture of CAP1391 ADSB and MLAT in the Goodwood /Selsey/Bognor Regis area from 15:40 to 16:15, after which it seems to be operating as purely Mode-S at a fairly consistent altitude of between 750 and 950ft until it returns to Goodwood at around 16:50.
The erratic nature of the Mode-S reports would mean that PilotAware would keep changing between known-position (when the MLAT is reliable) and Bearingless (when it is not) and the aircraft would be reported as such on SkyDemon (provided you had 'Show Bearingless Targets' enabled). This would certainly explain (at least as far as I can tell from what you have sent us) what you were experiencing - i.e. intermittent known position reports from the poor MLAT/CAP1391 interspersed with random intermittent Bearingless target reports from the Mode-S - NOT the CAP1391.
It's certainly one of the most erratic reports I have ever looked at. If it was my aircraft I would be extremely concerned about the poor quality signals which appear to be being transmitted from it - with ADSB CAP1391 (perhaps understandably) only reporting out to less than 10Km, but my greater worry is the extremely poor quality of the MLAT reports which may well indicate a problem with the aircraft's Mode-S transponder.
Best Regards
Peter
p.s. you can check this for yourself at https://playback.pilotaware.com/playback/groundstations/ by selecting the Transmission Type, putting in the ICAO code and Start Time (3 hour segments max, though shorter periods give a more detailed expanded report) and clicking on 'Search'.
Thank you so so much! All super interesting and very details and triggered lots of thoughts, so might not be a short answer from myself either as some points are carry over from the original post idea and some completely new :)
1) The erratic behaviour you shared – does that mean that if I have mode-s 3D enabled – I am fairly likely to be displayed with similar output in my PAW? If so – I must admit I would probably go for disabling the 3D MLAT as got me thinking that I might be wrongly looking for a plane in a certain direction, so rather look all around due to a bearing less notification.
2) I in fact flew today and experienced a situation when an aircraft was first showing as bearlingless target and then next minute as a specific position. My Mode S 3D was disabled then, so in such circumstances it would totally make sense that possibly that other aircraft had some portable device that was visible sometimes to my PAW but not always. See first screenshot attached.
3) I have to point out that original question is unfortunately still remains a bit of a mystery because it was not really about MLAT or anything. I know for sure that they left a CAP1391 on by mistake in a parked and completely shut down aircraft and I was only 50m away from it, but still saw it as bearing less through PAW (second screenshot).
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Also found the following log line:
$PALOG,20230417,152910,PAWRT,40632D,1,A,1,C,1,S,0,ES,0,P,0,F,0,U,0,M,00,valid,00,vers,00,nacp,00,nica,00,sil,00,sils,*07
which sounds like a signal was decoded as Mode AC only? As it was on the ground with engine off for a long time – there is no doubt on my side that that all standard electrics including normal onboard transponder were completely off at the time...
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Hi Alex,
Sorry for the delay in replying. I was away at Popham all weekend so rather busy, then had to fly all the way back up to East Fortune.
You still haven't given us your actual current PAW software version - it is reported on the first line of each track file, including the one you quote from in your latter post.
Thank you so so much! All super interesting and very details and triggered lots of thoughts, so might not be a short answer from myself either as some points are carry over from the original post idea and some completely new :)
1) The erratic behaviour you shared – does that mean that if I have mode-s 3D enabled – I am fairly likely to be displayed with similar output in my PAW? If so – I must admit I would probably go for disabling the 3D MLAT as got me thinking that I might be wrongly looking for a plane in a certain direction, so rather look all around due to a bearing less notification.
No definitely not - enabling Mode-S 3D simply allows you to see Multilaterated (triangulated) Positional Targets Reports for Mode-S aircraft where these are available, instead of just Bearingless Target Reports. It has no effect whatever on the performance of your own aircraft transmissions. My advice would always be to enable Mode-S 3D as soon as you are fully aware of what it does and how it works (which is why it isn't enabled by default).
2) I in fact flew today and experienced a situation when an aircraft was first showing as bearlingless target and then next minute as a specific position. My Mode S 3D was disabled then, so in such circumstances it would totally make sense that possibly that other aircraft had some portable device that was visible sometimes to my PAW but not always. See first screenshot attached.
Unfortunately the screenshots are a bit poor to see exactly what they are reporting (especially the one with the red ring). Even zooming in, I simply can't see enough to confirm whether the two reports are from the same aircraft. Assuming, however that they are, that would be perfectly normal expected behaviour for a Mode-S aircraft if you had Mode-S 3D enabled. Mode-S displays as Bearingless (so a circle on SD with Relative Alt - and Reg ID if 'Show Registrations' is selected in SD Nav Options) when you have NO ATOM, iGRID or SkyGRID uplink. It then swaps automatically to a 'known position' target if you get a Mode-S 3D report from ATOM, iGRID or SkyGRID, then drops back to Bearingless if you lose the uplink(s) again. I note, however, that you say you had Mode-S 3D disabled. In that case the signal must have been swapping between raw Mode-S and CAP1391 (or PilotAware) - so between Bearingless and Known Position - which fits with what I found in my analysis of your earlier track reports for G-NXOE). PAW would then prioritise the 'known position' reports while they were being received (even from a weak CAP1391 or PAW signal) but would drop back to a Bearingless Report with no position whenever the CAP1391/PAW signal dropped out.
3) I have to point out that original question is unfortunately still remains a bit of a mystery because it was not really about MLAT or anything. I know for sure that they left a CAP1391 on by mistake in a parked and completely shut down aircraft and I was only 50m away from it, but still saw it as bearing less through PAW (second screenshot).
That is still a bit of a mystery.
The lower screenshot 'appears' to show G-NXOE reporting as 'Mode-S + ALT' - or we a.) wouldn't have a Bearingless ring, and b.) wouldn't have the Aircraft Reg showing. If it was only transmitting Modes A/C, it would report as 'C-xxxx'). The REG 'might' of course be coming from the SkyEcho, but I can't see how you would get a Bearingless ring associated with it - except as I explained earlier that there was a very short-term glitch in (I think) the Ground Station Software, which was reporting some CAP1391 units as DF17 - which is the mode transmitted by Mode-S/ES (ADSB) Transponders. That fault was however found and fixed extremely quickly, so shouldn't 't have persisted (hence why I need to know the PAW software version that was in use at the time of your log.
My log decoding skills are a bit rusty (I usually leave that to Lee), but your reported log-line certainly does seem to show G-NXOE reporting as Mode A/C - and not Mode-S or S/ES (ADSB), sorry I can't remember what the rest of it means. That might be explainable if the transponder had been left in 'Standby' or 'Ground Mode' or has a Squat Switch, to stop full transmission until in the air.
I still thing it's an issue with G-NXOE.
Best Regards
Peter
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Thank you so much for being so detailed an helpful once again :-) and hope the event went well!
So, the software version was 20230316
1) Apologies I probably sounded a bit confusing here. So it was nothing about transmission really... In the screenshot attached (hopefully readable) is playback of me flying GLOOC that only had Mode S transponder and sub sequentially MLATed by PAW atom network on the morning of 19th of April. The playback contains a big "jump" to the south, which did not occur in reality. So, if my friend was in another aircraft nearby with PAW and 3D Mode S enabled, then it sounds like s/he would see GLOOC quite far away from the actual position?
2) Thanks a lot! All makes sense. I was able to figure out from your playback system that that aircraft likely had Mode S + PAW, so what you explained totally makes sense and no questions on it.
3) GDBOD is another aircraft that was just next to GNXOE. It is a club aircraft that also normally has a CAP1391 onboard, also was parked and completely shut down, so I am very reluctant to agree that something was not right with the transponder as both aircraft were definitely off completely. I need to see if I can reproduce the issue myself, but I don't have a 1391 device available, so need to ask someone.
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3) GDBOD is another aircraft that was just next to GNXOE. It is a club aircraft that also normally has a CAP1391 onboard, also was parked and completely shut down, so I am very reluctant to agree that something was not right with the transponder as both aircraft were definitely off completely. I need to see if I can reproduce the issue myself, but I don't have a 1391 device available, so need to ask someone.
The most common CAP1391 device is the SkyEcho 2, it is totally autonomous, and if not specifically shut down on the power button on the front of it, it will stay up and not go off with aircraft power. It will then stay up until the battery goes flat, 12 hours?
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Exactly right! So what I think the issue is that when aircraft is shut down - a SE2 likely to be left on. An easy thing to miss as I sometimes have forgotten to unplug power from my paw in the past
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So I attempted to replicate the issue… didn’t have much time, so I admit I did not see bearingless ring in SD, but I didn’t see the SE2 position either. On traffic page the aircraft of interest (GDBOD hex 40632C) was showing as CS only.
In the log found the following line:
$PALOG,20230516,162817,PAWRT,40632C,1,A,1,C,1,S,0,ES
Any more thoughts or suggestions of what I should try?
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Can you please confirm if G-DBOD has a transponder
Also was the se2 detected by ANY receiver?
Also, how close were you to the unit during the test ?
Thx
Lee
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Hi Lee,
I just borrowed the SE2 from the aircraft owners for 5 minutes for my testing, so I suppose what the actual aircraft has is less relevant? But normally the aircraft is flown with a Mode S transponder + SE2.
The SE2 was visible on a flight tracking app - same as before with exact position and ADSB source confirmed. I placed it a few meters away i.e. my PAW was inside an aircraft and the SE2 on tip of the wing.
It was purely stationary ground test with no engines running or anything.
Regards,
Alex
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Any more thoughts or suggestions of what I should try?
A skyecho has a vso setting
Anything less than this and it will not emit a position report
Can you check its setting
Does the CAP1391 have the setting for flying/not flying enabled? I think the default may be 10 knots to switch over? Been a while since I looked...
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I must admit I was in a rush and didn’t look at that to be absolutely sure, so will make sure to confirm. However, don’t see how it would show on a plane tracker if it wasn’t transmitting… hence I am quite sure setting is set to transmit always, but will check
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Ok, so…. This time I spent a good amount of time trying different settings of a SE2.
I tried:
1) transmit setting at 0 kts and at 10 kts
2) position SE2 within 2-3 meters of paw and within 10-15 meters of paw
3) Ensured that the actual aircraft was parked and OFF
This time I did not manage to replicate the bearingless target issue in any configuration…in fact, initially SE2 signal did not show at all. After a couple of reboots it did show on SD via PAW with either transmit setting and distance from PAW.
Very inconclusive tests to be honest… the only thing that remained consistent was that SE2 was always visible on a flight tracking app (even when not visible on PAW). I know for sure that in principle (and probably in most cases) I do see SE2 from flying aircraft. But what happened here will still remain a mystery.
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Hi again Alex,
Thanks for the further update.
Ok, so…. This time I spent a good amount of time trying different settings of a SE2.
I tried:
1) transmit setting at 0 kts and at 10 kts
2) position SE2 within 2-3 meters of paw and within 10-15 meters of paw
3) Ensured that the actual aircraft was parked and OFF
This time I did not manage to replicate the bearingless target issue in any configuration…in fact, initially SE2 signal did not show at all. After a couple of reboots it did show on SD via PAW with either transmit setting and distance from PAW.
SE2 shouldn't show on PAW or the flight tracking app if its Tx setting was set (and saved) at 10Kts, unless the unit was moving at more than that threshold speed. If as you say, it was reporting on SD via PAW (and on the flight tracking app) after a couple of reboots with either transmit setting, (and when presumably stationary), that would indicate that the VSO setting in the SE2 clearly isn't working as it should.
Very inconclusive tests to be honest… the only thing that remained consistent was that SE2 was always visible on a flight tracking app (even when not visible on PAW). I know for sure that in principle (and probably in most cases) I do see SE2 from flying aircraft. But what happened here will still remain a mystery.
That is entirely possible. You must remember that flight tracking apps use multiple receivers with high-gain antennas to pick up 1090 Traffic Signals from multiple directions. These are then combined before being presented on the app, so the app can often report weak transmissions where the signal might be obscured from an individual PilotAware, SE2, (or any other aircraft-based receiver) by metal or carbon fibre, human body tissue or any other non-RF-friendly components in a specific aircraft equipped with PAW, SE2, or any other receiver. This is why we strongly advocate the use of externally mounted antennas wherever possible (which of course isn't possible with SE2).
Best Regards
Peter