Ghosting?

[Charliesixtysix]

You should get a PilotAware, then you could see the rest of us! 

And you can connect the PowerFlarm into it, so you'd get the lot.

Not a bad idea Paul and one that we will most likely do soon.

However, as far as I can see no one has answered the OPs' query as to why he was seeing us labelled up close to him and at a similar height, when we were transmitting ADSB-out from fifteen or more miles west of him and some 3000 ft above.

Ideas?

[Paul_Sengupta]

Do you both have GPS tracks to maybe send to Lee and has the OP sent the PilotAware log?

[Charliesixtysix]

I'll pop mine over when I am next in the office but that will not be until 13th Nov.

[exfirepro]

Paul,

Dave did try to attach the track log to a previous Forum post, but of course it's far too big. I did suggest using Dropbox, but he may have missed my suggestion, or not know how to do so. If this is the case Dave, please get back in touch.

However, as far as I can see no one has answered the OPs' query as to why he was seeing us labelled up close to him and at a similar height, when we were transmitting ADSB-out from fifteen or more miles west of him and some 3000 ft above.

Ideas?

Without the track log(s), it is very difficult to answer this. In my years of testing, I have NEVER experienced a 'false alert' from a known position aircraft and have only ever heard of two instances (IIRC in the Project Eva Trials Report) where due to a technical issue, one of the aircraft was transmitting its position as the wrong side of the Greenwich Meridian.

The only way we will be able to resolve this issue properly is to look at Dave's PilotAware Track Log, however re-reading the thread yet again, the following points are clear.

Firstly, Dave says of the first alert on his 'inbound' flight to Cromer [My Edits....]

The aircraft on my inbound flight to Cromer was G-CCZD... [ - ]... it looked less than a mile at 12 o'clock (and stayed at 12 o'clock when I started the lookout weaving turns, so I'm guessing bearingless). So in fact, if he was a bearingless target, he could have been anywhere, as well as dead ahead, yes?

Regards,
Dave

The fact that the 'indicator' stayed at 12 o'clock on Dave's screen while he carried out his clearing turns indicates fairly positively that what he was seeing was a bearingless contact indicator. If this had been a known position aircraft (P3i or ADSB), it would have moved round on the screen away from the 12 o'clock position as Dave turned his aircraft (the amount of movement would of course depend on how big / prolonged the clearing turns were, but nevertheless the contact would have moved to some degree). It's also correct that a bearingless aircraft 'could' have been 'anywhere' [round 360 degrees, at the relevant altitude indicated on screen] as well as dead ahead.

A fault with G-CCZD (if for example the PowerFLARM temporarily stopped sending GPS data to the transponder), would cause G-CCZD to (temporarily) revert to Mode S, however it is unlikely that Dave would receive a bearingless target 'Alert' from G-CCZD's Trig TT21 at 15Km. Even if Dave was running Mode C/S Detect on 'Long Range', aircraft normally need to get much closer than this before bearingless target alerts start to appear on screen - except in the case of CAT aircraft running high power transponders!

Is it possible that what Dave saw was a bearingless alert from a CAT Mode S (e.g. Flybee) at long range and somehow confused this with the ADSB alert from G-CCZD, which would have been easily visible at this range, ....or was there a temporary fault on G-CCZD's transponder? Only a hypothesis, and no disrespect or criticism whatsoever intended or implied to either Dave or G-CCZD, but without seeing the log(s), these are the only explanations I can think of that make any sense whatsoever.

As I say, the logs will reveal all - if you can get them to Lee, Dave.

Regards

Peter

[Charliesixtysix]

All understood, thanks ( and absolutly no need to worry about airing possible failures, we are all here to learn).

Pretty sure our ADSB was working at the time for two reasons:

1) In the event of loss of gps, the Trig flags up an ADSB error message on the screen and we saw none.
2) I reviewed the  Flarm .igc trace after the event and it shows solid gps logging all the way on that flight.

As I mentioned earlier, I shall send the trace ( via dropbox) on my return to the office next week.

PS range at the time of reported hiccup was in region of 15Nm ( not km), not that it makes much difference other than it being even more unlikely that Dave would have seen a TT21 pure Mode S alert at that range.

[exfirepro]

Thanks for the update. All understood. Hopefully we will get to the bottom of this soon 

Regards

Peter

[exfirepro]

Thanks both

Yes I am using the latest PAW version and 'bearingless targets' is on. Obviously there is a difference between Mode C and Mode S signals, but are you saying the threat levels are treated differently with Mode C or Mode S?

I've checked the logs on the days in question but only Mode S equipped (or ADSB-OUT or PAW) show up when I know I was close to Mode C squawking traffic. I'm flying later in the week and will check again

Peter G,

The main difference between Mode 'S' and Mode 'C' is the lack of a 'Hex' identifier linking the data in the Mode C transmission to a specific aircraft. When we first started reporting Mode 'S' on PilotAware, it was 'relatively' easy to use the Hex identifier transmitted as part of Mode 'S' to establish which data was coming from which aircraft.  Unfortunately, Mode 'C' transponders, don't transmit a Hex address, so we have to 'analyse' all altitude responses from bearingless aircraft very carefully (and for a bit longer) to establish whether they come from a Mode 'C' transponder or are a Mode 'C' 'altitude' response from a Mode 'S' transponder (for two aircraft at the same altitude, the transmitted data packet is the same). Once identified however, 'threat levels' between Mode C and Mode S are treated exactly the same - but at any point in time SkyDemon can only display one bearingless target presenting the highest perceived threat. Also, although the targets all appear on the PilotAware Traffic Screen, threats will only be passed to the Nav device if within your chosen PilotAware bearingless target altitude filter range (show within vertically) and dependent on your chosen Mode C/S Detect 'Range'.

Remember also that Mode C transponders only transmit in response to an interrogation from a Radar Head or aircraft TCAS system, so won't transmit if out of radar coverage.

Regards

Peter

[PeterG]

Thanks for that. It shows how tricky things are for you.

Peter

[Admin]

Hi Dave,

Lee, I think you've answered my question, because in reading your replies carefully, I begin to understand a bit more about how PAW works. The aircraft on my inbound flight to Cromer was G-CCZD - I don't think I can attach the track file as it's 5.2Mb and apparently I can only attach 512Kb? I don't know what kind of contact it was - I don't recall an audio warning and I'm not sure of the difference between the other types of warning. The pilot of 'ZD said he had an ADSB output if that helps. By very close, it looked less than a mile at 12 o'clock (and stayed at 12 o'clock when I started the lookout weaving turns, so I'm guessing bearingless). So in fact, if he was a bearingless target, he could have been anywhere, as well as dead ahead, yes?

Finally got time to investigate.
I can tell you this aircraft did come close to you, the closest he came was here

Code: [Select]

$PFLAA,3,149,-559,151,1,404B40!GCCZD,32,,49,1.5,8*79
$PFLAA,3,211,-522,150,1,404B40!GCCZD,34,,49,1.5,8*7C
$PFLAA,3,253,-498,150,1,404B40!GCCZD,36,,49,1.5,8*78
$PFLAA,3,285,-474,150,1,404B40!GCCZD,40,,48,1.5,8*71
$PFLAA,3,330,-439,150,1,404B40!GCCZD,42,,48,-1.5,8*58
$PFLAA,3,334,-444,151,1,404B40!GCCZD,44,,48,-1.5,8*51
$PFLAA,3,414,-373,151,1,404B40!GCCZD,46,,48,-1.5,8*55
$PFLAA,3,449,-338,143,1,404B40!GCCZD,47,,47,-1.5,8*5F
$PFLAA,3,482,-313,151,1,404B40!GCCZD,47,,47,-1.5,8*52
$PFLAA,3,514,-273,143,1,404B40!GCCZD,52,,47,-1.5,8*5C
$PFLAA,3,547,-232,143,1,404B40!GCCZD,55,,47,-1.5,8*58
$PFLAA,3,553,-234,143,1,404B40!GCCZD,55,,47,-1.5,8*5B
$PFLAA,3,599,-171,143,1,404B40!GCCZD,57,,47,-1.5,8*5D
The fields are
PFLAA, <Threat>, <Metres N>, <Metres E>, <Metres Above>

so for example

Code: [Select]

$PFLAA,3,334,-444,151,1,404B40!GCCZD,44,,48,-1.5,8*51334 Metres North
444 Metres West
151 Metres Above

I think PilotAware was doing its job correctly, if it helps, this was your GPS Position at the time

Code: [Select]

$GPGGA,122901,5253.557,N,00119.023,E,1,10,0.9,60.4,M,45.8,M,,*76
Paste the above into here
https://rl.se/gprmc

If you have a specific time for when you thought there was a threat I could take a look at that moment.

I also saw some ModeS Warnings of less than a 50ft below for GRVUK

Code: [Select]

$PFLAA,3,1500,,-12,1,405020!GRVUK,,,,6.1,8*30
$PFLAA,3,1500,,-14,1,405020!GRVUK,,,,6.1,8*36
$PFLAA,3,1500,,-14,1,405020!GRVUK,,,,0.0,8*31
$PFLAA,3,1500,,-16,1,405020!GRVUK,,,,0.0,8*33
$PFLAA,3,1500,,-17,1,405020!GRVUK,,,,0.0,8*32
this generated audio messages (if you are connected)

Code: [Select]

$PALOG,405020,AUDIO,MODES,,,189*60
your position was here when this threat was raised

Code: [Select]

$GPGGA,121735,5257.118,N,00102.552,E,1,09,1.0,244.4,M,45.9,M,,*4B
Thx
Lee

[Charliesixtysix]

Lee,
Thanks for looking into this.

However, I have some doubts that this bit of the flight is where the initial reported in flight conflict/ warning occured

I certainly did come close to him at the location indicated above and would hope that  it would have generated the report you highlighted - because, if I am reading it right, that was at Cromer airfield where we both landed( and the time coicides with his final approach and touchdown as I entered the  circuit at around 600ft under low cloud - the time matches Dave landing and my touchdown some two minutes later.

His inital report ( as described to me by Dave himself) of the in flight conflict alert was some minutes earlier than that when he was west of Cromer at around 1000ft agl and I was some fifteen miles further west than that and quite likely several thousend feet higher than him.

Ishall send my file to you tomorrow in the hope it might help.