PilotAware
British Forum => Technical Support => Topic started by: RobertPBham on September 12, 2016, 03:17:44 pm
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Hi all,
Just got back from a fly out this weekend to Jersey with the club I am with - first trip across water and overseas and it was amazing.
I'm sure your not interested in my trip ramblings but spotted the following when I was flying over the water to Jersey - five aircraft made the trip and as I got over the water a bearing less alert appeared on SkyDemon - it was picking up one of the club planes. I spotted the reported aircraft - approximately 1/2 KM ahead and about 200 feet above. SkyDemon was reporting the aircraft as -0.2 - now I thought this meant they were below us and originally that's where my scan started. Does the -0.2 mean distance from my aircraft or is it height - it it's height is there any reason it was reported below (in my understanding) or am I understanding the -0.2 incorrectly and it means that my aircraft is 200 feet below the reported target.
Thanks
Rob
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Hi Rob,
Well done... I bet you enjoyed your trip. I well remember my first channel crossing. I left Headcorn with a colleague, but he took off like a scalded cat heading for Dover, so I just dawdled along on my own at 5,500ft casually taking photos of ships and the view. Had I realised that one of my mags had accidentally got switched off (long story), I might have been more concerned, but flying from East Fortune we get used to flying over water so wasn't concerned 'til my engine eventually gave out on final into Abbeville - very embarrassing when I realised why!
The figure attached to the bearingless target ring denotes the relative altitude of the other aircraft to your own, so should as you say have been showing as +0.2 if the other aircraft was definitely 200ft above you. It is possible for the reported relative altitude to vary slightly within the tolerances of the technology, but 400ft out seems excessive. Is it possible that the alert you saw was coming from one of the other aircraft in your group - perhaps below you and behind rather than the one you saw in front and above you?
Regards
Peter
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Hi exfirepro,
Your trip sounds very interesting - mine was no where near as exciting! It was a great experience though - stopped off at Alderney on the way back - I was a passenger on the way back so managed to get some great photos.
I'm sure it was the club aircraft ahead and nothing behind - we were the last two across the water (us being the last plane). I tracked G-RU for a good 20 to 30 minutes and the alerts displayed the call sign and then the height (as I remember it). The alerts varied from -0.2 to -0.8 - there attitude seemed very stable to ours so not varying very much in that time. I've checked the SkyDemon log and my altitude was between 2200 and 2400 for the time we were behind G-RU - they were always above and ahead of us - at approximately 1 o'clock. We were in contact with various control zones and had no other reports of traffic behind and below - especially that close.
There's a possibility the PilotAware antenna was at an angle in my bag - I don't think this should effect the reading but just thought I'd mention it.
Thanks
Rob
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Hi again Rob,
No, the angle of your PilotAware antenna(s) might have had an effect on signal strength, but shouldn't have any effect on the reported altitude.
Judging the altitude of another aircraft relative to your own in flight is always difficult, however if as you say the bearingless target ring was displaying -0.2 to -0.8 with the aircraft always ~200ft above you as you saw it, this would mean a reporting error of between 400 and 1,000 feet - which I would certainly not consider to be within tolerances. It's unlikely, but I do know of one case of a faulty barometric sensor on a PAW bridge, which could certainly lead to incorrect altitude reporting. Next time you are flying, check the barometric pressure reported on your PilotAware Home Screen against the actual QNH setting from your own altimeter before you take off. If there is a significant variation please let us know. As I say, not likely, but possible and worth checking.
Regards
Peter
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Hi Peter,
I'll definitely check that and report back.
One uncertainty - the day before I had a flight and had set the incorrect QNH - SkyDemon was reporting the correct altitude - I know this as it alerted me to airspace above at the same time a friendly controller did! Does SkyDemon use the barometric sensor from PAW? If so, I'm sure the sensor is fine.
Also the SkyDemon log from from flight to Jersey matches the altitudes I was flying - all assuming it's using the PAW sensor for this though.
Thanks
Rob
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I believe Sky Demon shows the GPS altitude.
It was my baro sensor which is faulty, but it shows about 5-6000ft out! However, with suction around the cabin, the pressure inside the cabin can be lower than static, and this will cause the baro sensor to think you're higher than you actually are. A couple of people have reported this sort of thing now. I suggested to Lee that a "calibration" setting be put in the menu to adjust accordingly. It could even suggest a value based on the GPS altitude (best to do while receiving EGNOS).
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I would advise against using GPS altitude to modify barometric.
The further away from ISA temperatures, and the higher you go, the further they will be apart. A manual method of syncing the baro chip to the QFE on the ground would be better.
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Just to clear up some possible confusion here:-
Altitude used in SkyDemon is the GPS altitude, whether you are using Location Services or PilotAware.
This is all derived from the GPS/NMEA data.
Traffic data that is passed to SkyDemon (and others) contains relative height differences.
In the case of ADS-B, Mode-C and Mode-S traffic data, the relative height difference is calculated using Barometric Pressure.
In the case of Mode-C this is only accurate to the closest 100ft, I recall in Mode-S/ADS-B it can be a higher resolution of 25ft
The original discrepency (if correct) was a 400ft discrepancy - which is pretty large.
First thing to check is the reported QNH on the PilotAware homepage, this will report both the Pressure and the calculated
altitude, please ensure these reported values are correct, if they are, then the issue is either the other aircraft pressure sensor, or this was not the aircraft reported.
One final mention, is that there was a fix in SkyDemon (last 2 weeks) which resulted in miscalculations for Mode-C/S traffic due to a metres to ft conversion
Final word on this, PilotAware to PilotAware traffic uses GPS altitude comparison, which seems to be a more accurate and finer resolution than Barometric.
Thx
Lee
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A manual method of syncing the baro chip to the QFE on the ground would be better.
This wouldn't help as the problem is the dynamic pressure within the cabin when the aircraft is at cruise speed.
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I've just had chance to pop in to Wellesbourne and jump in to a plane - no flying so all of this was tested on the ground.
Wellesbourne QNH was 1008Mb as reported by the tower.
PAW QNH was 1009mb, QNE was 265ft and GNSS was 154ft.
On the ground there doesn't appear to be a major discrepancy - not sure how this translates to in the air though. I would guess the pressure could be quite different inside the cockpit to outside and hence the possible discrepancy?
If I get some aircraft time I'll try and see what the reported details are in the air.
Thanks
Rob
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On the ground there doesn't appear to be a major discrepancy - not sure how this translates to in the air though. I would guess the pressure could be quite different inside the cockpit to outside and hence the possible discrepancy?
Hi Rob,
is it a pressurized cabin ?
If not there should be no discrepency.
Thx
Lee
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If not there should be no discrepency.
Many enclosed aeroplanes have a slightly lower cabin pressure due to the suction effect of the airflow around the fuselage.
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Hi Lee,
It's not a pressurised cabin - the test was done on the ground with the door open on a stationary PA28. Only using the plane to get the QNH from the tower.
Sounds like I may have a faulty sensor if that is the case!
Thanks
Rob
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Sounds like I may have a faulty sensor if that is the case!
Hi Robert,
Hmm, this looks pretty accurate to me
Wellesbourne QNH was 1008Mb as reported by the tower.
PAW QNH was 1009mb, QNE was 265ft and GNSS was 154ft.
What makes you think it is faulty ?
my comment
If not there should be no discrepency.
Was referring to the fact that either the A/C you saw was not the A/C reported by PAW
or the plane you saw was not returning the correct ALT
or the version of SkyDemon has the bug I mentioned earlier
As Peter mentioned earlier, the Track files will tell us diffinitively, we are just postulating at the moment.
(Edit: that was another thread, doh, are you able to supply the track file from your flight ?)
Finally, was the discrepency you observed an ADS-B, ModeC or ModeS return ?
and do you possibly know the reg of the A/C you had a visual, we can check this against the track file
Thx
Lee
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A manual method of syncing the baro chip to the QFE on the ground would be better.
This wouldn't help as the problem is the dynamic pressure within the cabin when the aircraft is at cruise speed.
Accepting that every individual aircraft could be slightly different, but every aircraft I've flown I flip to alt-static just to see the effect on altitude and airspeed, so I know what to expect if I have to do it for real. I don't think I've ever seen anything greater than 1 or 2 mb, say 50' in altitude, i.e well inside the tolerance for an altimeter anyway.
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Well Rob, didn't you open a can of worms here!
Thank you for checking your PilotAware QNH against your aircraft / local tower as I requested. As Lee has already said - your test (within 1mB - i.e. within 30ft of the reported 'Tower' QNH) is well within tolerance for PilotAware - or any other pressure based setup. I would therefore certainly not be concerned about your Baro sensor. I had already considered the 'known' issue whereby the current version of SkyDemon can misrepresent relative altitude due to a conversion issue between height reported in metres and feet (which by the way has been corrected in the latest Beta version of SkyDemon, which I tested this morning and which should be released later this week) and had ruled this out as a likely cause as the reported relative altitude difference is usually far greater then the 400ft you originally reported.
If you can as suggested provide Lee with your track log and both aircraft's registrations, he will be able to check this for you. Otherwise I suggest updating SkyDemon as soon as the new release comes out (your device will notify you) and let us know if the problem persists after that. If so I would suspect a defect with the other aircraft's pressure reporting or as Lee and I have both suggested, that the aircraft displaying on your screen was NOT the one you were observing.
Regards
Peter
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Hi Lee,
Sorry - I thought when you mentioned there should be no discrepancy that it was faulty - I didn't think there was a big issue with 1mb. :-)
I'm happy to supply the track file - the aircraft I was following was G-WARU - it was a mode C or S target as it was bearing less.
Who should I send the track file to?
The version of SkyDemon I have is the latest - from the Apple App Store - not sure if this one has the bug or not.
I'm not too worried as you mentioned it could be an issue with the other aircraft reporting height but just thought I'd mention it in case I was interpreting things incorrectly.
Thanks
Rob
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And sorry for opening a can of worms! :-)
This was my first real chance to test and see the bearing less target alerts in action - following another club aircraft at a safe distance and seeing the information appear. I've checked the track file using the Java app that you can download from the site - I cannot see G-WARU registration in the track file - I've been through virtually every listed plane using the app and none are closer than 7KM (I may have missed a plane).
Thanks
Rob
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Hi Robert
Dont forget bearingless have no coordinates, hence no range, so nothing to show ini the post processor.
If you give me access to the trk file and an approx time I may be able to work it out
Thx
Lee
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That explains it - can I email it to you? It's 7MB - compressed using 7Zip is 603KB.
I can approximate the time - it will be 1 hour 15 minutes in and I'm sure we were following G-WARU for a good 30 to 45 minutes. The plane I was flying was G-GYTO.
I've just opened the track file in Notepad++ and still cannot find WARU call sign listed - odd as when I saw the alert on SkyDemon I know that's the call sign list - I mentioned it to people in the plane - one of them was taking photos of it while we followed and said it's definitely WARU with the zoom lense in action.
Thanks
Rob
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Hi again Rob,
I was only joking about the can of worms. ;) I thought you told me your flight was uneventful!! Not so the post-flight analysis it would seem. All part of the learning curve. Lee will no doubt be able to use his 'magic' to get to the bottom of things and let us know what he finds.
Best regards
Peter
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Hi Peter,
I know you were joking! :-)
I've had a bit more of a nosey at the track file in Notepad++ and am guessing that you are listing the Mode C and S targets via Hex ID rather than call sign? I converted the clubs aircraft call signs to Hex ID's and can find many occurrences within the file.
I have no idea what the other numbers mean though on each line but interesting all the same - I like to investigate things. The hex ID occurrences appear towards the middle to end of the file so would tally roughly with the times I mentioned and the detections.
Thanks
Rob
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Hi Robert,
Can you tell me the settings you have selected for
Mode-C/S
- Separation
- Detect
- Select
Initial findings, PAW started running at 10:13:08 (Zulu Time)
so 1:15:00 into flight would be about 11:28:00
at 11:32:01 I see the following
$PFLAA,3,1500,,741,1,,,,,,0*72
this indicates an A/C 741 metres above - 2431 ft, in SD this should have been shown as 2.4
then at 11:32:49
$PFLAA,3,1500,,-1,1,,,,,,0*5C
this indicates an A/C 1 metre below !
This repeats for 10 seconds, very close, or at your height
$PFLAA,3,1500,,-1,1,,,,,,0*5C
$PFLAA,3,1500,,-2,1,,,,,,0*5F
$PFLAA,3,1500,,-3,1,,,,,,0*5E
$PFLAA,3,1500,,-4,1,,,,,,0*59
$PFLAA,3,1500,,-3,1,,,,,,0*5E
$PFLAA,3,1500,,-2,1,,,,,,0*5F
$PFLAA,3,1500,,0,1,,,,,,0*70
$PFLAA,3,1500,,1,1,,,,,,0*71
$PFLAA,3,1500,,2,1,,,,,,0*72
$PFLAA,3,1500,,5,1,,,,,,0*75
this should have shown in SD as 0.0
more importantly, it sounds like you are receiving your own transponder, which is why I wanted the settings above, this repeats a few times whilst I presume your transponder is interrogated.
I then see an A/C at 11:42:09
$PFLAA,3,1500,,-355,1,,,,,,0*5E
1100ft below
I then see an A/C at 12:03:02
$PFLAA,1,4500,,283,1,,,,,,0*7E
928ft above
There are lots more contacts, but this looks like the period you were referring to.
Thx
Lee
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Wellesbourne QNH was 1008Mb as reported by the tower.
PAW QNH was 1009mb, QNE was 265ft and GNSS was 154ft.
Hi Robert et Al
Sorry for getting to this thread a bit late but my internet has been out for 3 weeks thanks to a thunderstorm and a VDSL modem that took a lighting strike.
So I was down at Wellesbourn today and have loaned them a PilotAware unit so that Jon in the tower can set up a virtual radar for you good PilotAware users when you are in cct. This will also allow you to take photos of your transmissions if you want to convert Mode S to ADS-B and present them to CAA.
However, the control tower is made up of two shipping containers stacked on top of each other with a pod on the top is at a rough estimate 20-25ft high. The difference between 1008 and 1009 Mb is 27.4ft so I think that we can discount the inaccuracy of the barograph.
Ken Richardson and Alan Brame? have both got PAW so we should get a little cluster going at Wellesbourne.
Robert I guess that when you are in circuit you should let Jon Mike, or Frankie know that you are Downwind PilotAware so that they get used to using the facility.
That would be great if the standard at all provincial and private airfields and airstrips became G-ABCD Downwind - PilotAware. Then you would know that you are being seen.
At the moment Wellesbourn, Tatenhill and Damyns Hall have set up or are in the process of setting up ground stations for this facility. Do you think thesis a good idea?
Cheers
Keith
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Hi Lee,
Thanks for looking at the track file - interesting findings!
I've checked the settings for Mode-C/S and they are as follows:
Display - Req-ID
Separation - +/- 4000ft
Detect - Medium Range
Select - Mode-CS(Beta)
I did originally think that the alert could be my plane as I thought I may have forgotten to change the Hex-ID within PilotAware - however, I checked this and it was set correctly for G-GYTO (40438D).
It is definitely possible that G-WARO was at a similar height to me before I spotted them when they were above - we were all following a similar course! I'm guessing that the Mode C and S targets aren't saving there call signs in the track file. I'm certain I saw G-WARU listed and a -0.2 on SkyDemon.
Looking at all the details you have found it appears that it could be just the SkyDemon bug with translating heights from metres to feet.
I'm happy to monitor once the new version is released. This has been the only opportunity I've really had to follow a plane and 'see' what happens with PilotAware etc.
Hi Keith,
Great news that Wellesbourne now have PilotAware - lets hope the airfield stays open!! Very interesting on the QNH - I always assumed it was taken from ground level but that would definitely explain the difference!
More than happy to let Jon, Mike and Frankie know I'm about with PilotAware - great to get them used to it - not sure on changing the phraseology for downwind though - completely understand the logic but it may add some confusion to anyone who doesn't know what it is - they will be thinking the Pilot is Aware of what?? Just my thoughts anyway!
Thanks
Rob
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Hi Rob
Aha!
OK, if you have a transponder, you should select the option with FILTER, this will attempt to remove your mode C return
Thx
Lee
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Hi Lee,
Now set to Mode-CS+Filter(Beta). I might be lucky as all the planes I fly have a transponder!
That may explain a few things with what's being reported in the logs! I'm hopefully flying on Friday, so will report back any further details although waiting for the new version of SkyDemon may be more sensible! I bet a won't be lucky enough to be following a plane! :-)
Thanks
Rob
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I think Derby are also setting up a ground station?
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I hope all these people are going to set them to 'Rx' only, the last thing we need are spurious traffic warnings springing up.
I wonder what software they will be using to display traffic, as it seems a bit clunky to use a full blown nav package in flight mode.
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I hope all these people are going to set them to 'Rx' only, the last thing we need are spurious traffic warnings springing up.
I was thinking that myself, Graham. The last thing you need on short final is a sudden unexpected danger warning from the tower :( (though in reality you would have 'seen' their PAW from several miles out).
Regards
Peter
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Hi Peter, Robert,
The basestation can be configured as
RX, or
TX/RX
I agree about not having false warnings generated,
so when the RF data is sent, it is tagged saying what the sending type is, ie type=basestation,
therfore it is very easy in S/W (at the receiver) to code up ignoring/icon-type/non-display of type=basestation
I am trying to do some forward thinking, and hoping to get the NAV tools to have different icons for the traffic/obstacle types,
at the moment in the display, you can have any icon type you want (so long as it's an aircraft ;))
but of course, in the future we will probably want :-
- Control Tower (basestation)
- Dynamic Obstruction (e.g. Crane)
- Dynamic Zoning (e.g. NOTAM)
- Static Obstruction (e.g. Windfarm, although these can generally be coded directly to the NavTool Database)
- Helicoptor
- Balloon
- Glider
- Drone (Dare I say!)
etc ...
Thx
Lee
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That sounds great with the obstacles icon types. Definitely helpful long term! I've had a couple of Mode S reports in the circuit and ignored them as they were reported ground level - the worst thing to happen with erroneous reports is that you start to automatically ignore them which is a danger!
Do we know how Wellesbourne is viewing the traffic - I can always go up to the tower and see but was interested in what they are expecting to see and how they are handling the information?
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At Wellesbourne Jon in the tower is very tech savvy as you will know from the weather website. Initially he is going to use his own personal copy of Sky demon. But I think that he will also investigate XC Soar, free and less cluttered as you say. Although I must add that sky demon can be very effectively de cluttered and works well.
Other brilliant navigation packages are also available 8)
Keith
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Not directly a PAW issue, I know, but I wired the audio from SD into the headset system for the first time. On final there were so many warnings about imminent collision with the traffic at the hold and on the apron that I had to physically pull the plug. Very distracting.
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Hi Richard
I guess that it's PilotAware doing its job. However it is distracting. We need to think about how to overcome this operationally in a better way than pulling the plug
Keith
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Just to confirm, this is SkyDemon audio NOT Pilotaware?
Have you reported to Tim at SkyDemon ?
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Yes, SkyDemon audio. I have not reported it to Tim, I assume it is the nature of the beast. Is it supposed to suppress warnings from A/C on the ground, or some such? After all, I was heading very close to someone at the hold.
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Hi Richard
I'm not sure of the algorithm used by Tim but you can be sure you are one of a small group who have exercised it, so please give Tim some feedback/reporting to help him refine his product
It would also be worth mentioning that we have track files to replay the events to help him reproduce your findings
Thx
Lee
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Hi Lee,
The trouble is, I can't make a very objective report. I heard a racket, and pulled the plug without even looking at the display. Good point about the files though, I will take a closer look.
Richard
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Hi all,
On Friday I had a trip to Newquay (arriving back yesterday).
This gave me a good chance to test with the new version of SkyDemon.
On the journey down we had one Mode C/S alert - this was for a helicopter 200 feet below us. The height was reported correctly (by eye) but the helicopter was rather close before it flagged up as an alert - approximately 500 to 1000 metres. We both knew of each other's presence as we were under controller (listening squawk) but I did think it was a bit close for comfort if you were unaware of the traffic!
This could be due to the positioning of my PAW but what is expected detection range and alerting range (horizontally)?
I had one alert close to Newquay of a plane at 0.0 but I believe this was our own plane being detected as none of us saw any other traffic. The weather was fairly rubbish on Friday so not much was about!
Thanks
Rob
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Hi Robert,
Bearingless Alerts are not based on distance but on received signal strength. The distance at which you receive alerts therefore depends on the power output and efficiency of the transponder system, the efficiency of your own setup and the 'Detection Range' you have selected in your PAW.
You should have received a series of 3 alerts - 'Traffic Notice', then 'Traffic Alert' and finally 'Traffic Danger' as the helicopter approached. Are you saying you didn't get these? We took a lot of care designing the trigger levels to cope with 'GA' strength transponders at 'safe' alert distances, so if not I would suspect screening of your ADSB antenna from the helicopter's transponder. Please let me know if this is likely.
Regards
Peter
Peter
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Hi Peter,
Thanks for the information.
As a rough guide the helicopter was at our 11 o'clock as we approached it. We then passed it as 9 o'clock (200m away and 200ft below) - we were heading south and it was travelling west - so approaching each other and going in different directions. I don't have the audio alerts as my PAW isn't connected to the internal comms system - I rely solely on the SkyDemon alert rings - I only received one SkyDemon alert and this was a yellow ring as I remember with the -0.2 - seem to roughly remember it did change to green once he had passed behind.
My PAW is set to 4000ft - I assumed this was height based but if horizontal as well, then it was a lot closer than 4000ft. Definitely a possibility shielding was an issue - PAW located in rear, passenger in front of that and then us pilots and engine!
Would you say it's a requirement to have the audio connected or should the SkyDemon rings be enough - I've never seen a SkyDemon ring alert at 4000ft - the most I've seen is 1000ft and that was on the trip to Jersey.
Thanks
Rob
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My PAW is set to 4000ft - I assumed this was height based but if horizontal as well, then it was a lot closer than 4000ft. Definitely a possibility shielding was an issue - PAW located in rear, passenger in front of that and then us pilots and engine!
Hi Rob,
These settings are for the Maximum Vertical Separation that will appear as warnings. Horizontal alerts for bearingless targets (the rings) are determined by the Range Setting in PAW, which as I said earlier is not based directly on distance. I normally fly on the 'Medium' setting, which generally gives me plenty of warning.
Would you say it's a requirement to have the audio connected or should the SkyDemon rings be enough - I've never seen a SkyDemon ring alert at 4000ft - the most I've seen is 1000ft and that was on the trip to Jersey.
In general PAW's audio warnings will alert you slightly quicker than the rings, so worth connecting it. They also mean you don't need to watch the screen so much, so are more likely to pick up aircraft visually - remember many won't appear on screen at all if they are not transponder, ADSB, or P3i equipped.
Regards
Peter
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Yes, the 4000ft is height.
Having the antenna down the back is possibly the worst place for it as you really want the longest range of detection being the direction you're travelling in. I have my PAW stuck up on my dashboard with a clear view ahead and to the sides, though shielded ahead and down by the engine and airframe. However, it might work ok if you increase the detection range (using lower signal strengths to alert) as transponders are reasonably high power. Might not work so well for P3i though.
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Hi Paul,
I'll give that a try next time I'm there. One of the main issues I have is cable length for the ADSB antennae - with both front seats occupied and passengers, trying to get somewhere to locate the PAW is difficult (hence it being in the luggage compartment at the back) - especially as they are club aircraft and I cannot permanently install the PAW.
Thanks
Rob
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I have stuck some rubber feet on the bottom of mine and place it on the coaming...
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I am new to PAW - in this thread there is mention of setting the "detection range" in PAW. How do I access this (and other?) settings? Thanks.
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Roger
To get to the settings you need to get to the PAW configurations page the link below will guide you to the correct area
http://www.pilotaware.com/wp-content/uploads/2016/09/160901-Initial-configuration.pdf
I hope this helps