Primarily for general aviation discussion, but other aviation topics are also welcome.
  • 1
  • 16
  • 17
  • 18
  • 19
  • 20
  • 29
User avatar
By gaznav
#1664185
In fact looking at it, the big circle and the other in the overlapping example are both EASA certified aircraft and so I thought they had to use certified GPS sources? I thought the SIL=0 stuff from Project EVA was for Annex II aircraft only or is that incorrect?

Project EVA: https://nats.aero/blog/wp-content/uploa ... report.pdf

According to this the original 9x trial aircraft were an RV6, Europa (x2), Bristell NG5, Jodel DR100, Skyranger, RV12, Falco F8L and a P&M Quick flexwing - all Annex II.
#1664196
gaznav wrote:In fact looking at it, the big circle and the other in the overlapping example are both EASA certified aircraft and so I thought they had to use certified GPS sources? I thought the SIL=0 stuff from Project EVA was for Annex II aircraft only or is that incorrect?


Hi Gaz,
How did you determine they were using non-certified GPS ?
The SIL=X is not supplied by the GPS itself, it is a value entered directly into the transponder, so you can connect a certified GPS to a transponder, and enter a figure of SIL=0 into the transponder.

I come back to my original point, that SIL and NACp are unrelated.
SIL is entered into a transponder as a static value
NACp is calculated dynamically by the figures fed to it from the GPS source

Thx
Lee
gaznav, Keith Vinning liked this
User avatar
By gaznav
#1664200
Hi Lee

I used to fly microlight HMCF and I’m pretty sure it was SIL=0 installation using an uncertified GPS. I also seem to recall a PAW was used (I need to confirm that), but I do know that it has a PAW and that they disconnected the audio as it was too noisy in the circuit where they flew. I’m not sure of the other 2 at all having a SIL=0 installation and also I checked the Regs to see that they were EASA airframes - hence my question whether they are using a certified position source with SIL>=1.

As I say, it’s just an observation at the moment on whether they are SIL=0 or SIL>=1 installations that are producing these large circles. I need to do a bit more digging to find out (I’ll be checking on Friday for the very big circle in the bottom screenshot) and also the microlight.
#1664205
In LAA MOD 14. the inspector must sign off on
Data settings SIL=0 and SDA=0 have been set as per the configuration guide (or SIL=1 for TABS devices approved to TSO C199) have been set as per the configuration guide.


My Aera 500 GPS receiver boasts WAAS position accuracy, but is missing a bit of paper to claim SIL=1. :(
gaznav liked this
#1664220
@gaznav

G-EDGA with the 15 mile radius is registered at RAF Halton, I presume you know that ?

**EDIT** looking at this again the Radius is 10nm which is the figure used in NACp (and measured on google maps)

Thx
Lee
Last edited by leemoore1966 on Thu Jan 10, 2019 10:14 am, edited 1 time in total.
gaznav liked this
User avatar
By PaulSS
#1664253
@Tim Dawson
Yeah, they look pretty bad. Not sure what the best course of action is. The airframes themselves are telling us, via adsb, that their position is uncertain to that degree, so we draw it. To not draw it, now that we’ve implemented that part of the protocol, would seem potentially misleading.



I think they look more than 'pretty bad'. I reckon they are a totally unnecessary distraction and cover up far too much of the map. Having them in a 'solid' circle of red really makes it look like something is very serious when, quite frankly it is not serious at all.

This display is similar to displaying another aircraft's ANP. I have absolutely zero interest in that at all, both professionally and personally. If he is outside limits AND the equipment is required to be within certain limits then it is up to the pilot to deal with ATC etc, not broadcast to everyone else that his kit may or may not be outside a probability circle. Nobody in the professional world needs to know another aircraft's ANP and that is even more the case in private flying.

I would say just because you have the ability to display it on Sky Demon does not mean you have to. It causes too much clutter and is unnecessary. The 'best course of action' in my view is to either get rid of the function or, if you want the option to have every bit of data displayed on an already-busy screen, at least give the user the chance to turn it off themselves.
Balliol, patowalker, gaznav and 1 others liked this
User avatar
By Tim Dawson
#1664262
It isn’t that straightforward. Aircraft which are telling us there’s a good chance they’re not where they say they are, are not considered for traffic warnings either. For hopefully obvious reasons.

We could suppress the big uncertainty circles and pretend everything is fine, but I’m not sure how helpful that would actually be.
leemoore1966, kanga liked this
User avatar
By PaulSS
#1664271
Thus far, we seemed to have coped quite admirably without knowing how good or bad another aircraft considers its equipment to be. It's fine for the driver of that aircraft to be aware if there's a snag with where his machine thinks it is but there's no requirement for all of us to know. I know your program is doing lots and lots of very clever stuff behind the scenes but I don't consider it's necessary that we be shown all of it. In my view those uncertainty circles are a retrograde step for a navigation app and smacks of being just a bit too clever, especially for the likes of dimbos like wot I is.
gaznav liked this
#1664283
Tim Dawson wrote:...We could suppress the big uncertainty circles and pretend everything is fine, but I’m not sure how helpful that would actually be.

Don’t shoot the messenger....
I empathise with your position here Tim (no pun intended), its a case of damned if you do, and damned if you don’t

If you were to suppress information, I could imagine the outcry if a situation occurs where information had been found to have been filtered out.

One thing I completely agree is that you cannot just ignore the uncertainty figure, I was one of the advocates who requested that you provided the ambiguity circles, I have to say I have been surprised by the amount of ambiguity in some cases of the ADSB position reporting

The genie is now out of the bottle, we know this is the case and cannot pretend it is not, so now how best to handle and represent the data ?

Could it be some of the transponders are overly pessimistic in defining NACp from the GPS data perhaps ?
There is no standard definition (as far as I am aware) of how NACp is determined from the GPS data

Thx
Lee
kanga liked this
#1664294
I'm at the limits of my technical knowledge here so please be gentle. :)

It's my understanding that NACp is an indication of the 95% accuracy of a GPS. Is this a static figure (ie related to the actual equipment) or is it dynamic (something more akin to RAIM)? Either way, the transmitting equipment (ADSB, PAW etc) needs to transmit this figure, or assign a level of uncertainty, and this is subsequently displayed by software such as SD.

If the above is correct, where is the weakness? Are we saying that the GPS chipsets aren't up to the task, either practically or from a regulatory perspective? Or is it as Lee intimates, an issue with the 'reading' of the GPS data by the transmitter element?
Last edited by Dave Phillips on Thu Jan 10, 2019 8:32 am, edited 1 time in total.
User avatar
By GrahamB
#1664296
leemoore1966 wrote:How did you determine they were using non-certified GPS ?
The SIL=X is not supplied by the GPS itself, it is a value entered directly into the transponder, so you can connect a certified GPS to a transponder, and enter a figure of SIL=0 into the transponder.

I come back to my original point, that SIL and NACp are unrelated.
SIL is entered into a transponder ....


I’m not sure you are necessarily correct on that.

AIUI, for example, the TT31 self-configures SIL according to the protocols configured on the interfaces between it and the source device; there is no way to set it manually.
leemoore1966 liked this
User avatar
By T67M
#1664298
One option might be to display the information a little less literally, for example by changing the the target in some way to indicate degraded, rather than drawing a circle showing the potential (15nm!) extent of ambiguity.

I do wonder if this might be easier if drawing the target aircraft using the normal TCAS symbology rather than little aircraft pictures. One option might be to colour the centre of the symbol to represent the threat level (as per TCAS) and changing the symbol to a different shape (e.g. triangle) or even using a dashed outline when NACp is greater than (e.g.) 1nm.
Flyin'Dutch', PaulSS, Nick and 1 others liked this
#1664301
T67M wrote:I do wonder if this might be easier if drawing the target aircraft using the normal TCAS symbology rather than little aircraft pictures. One option might be to colour the centre of the symbol to represent the threat level (as per TCAS) and changing the symbol to a different shape (e.g. triangle) or even using a dashed outline when NACp is greater than (e.g.) 1nm.


I think that would be a good thing (the normal TCAS symbol)
gaznav liked this
User avatar
By neilmurg
#1664303
GrahamB wrote:
leemoore1966 wrote:....I come back to my original point, that SIL and NACp are unrelated.
SIL is entered into a transponder ....
I’m not sure you are necessarily correct on that.
AIUI, for example, the TT31 self-configures SIL ....
But SIL and NACp are still unrelated (AIUI)
I like @T67M 's idea that the circle doesn't have to be the radius reported by the device. In the example the radius looked like 7.5 miles, 15 miles diameter, still surprisingly large, but let's not inflate the size of everything.
The aircraft's position is NOT equally likely to be at every point inside the circle, and the plane doesn't cover that much of the landscape either!

However, we aren't going to design an app via the Flyer forum are we, 'cos, you know, not all information given is as accurate as it claims.
Shoestring Flyer liked this
#1664305
GrahamB wrote:
leemoore1966 wrote:How did you determine they were using non-certified GPS ?
The SIL=X is not supplied by the GPS itself, it is a value entered directly into the transponder, so you can connect a certified GPS to a transponder, and enter a figure of SIL=0 into the transponder.

I come back to my original point, that SIL and NACp are unrelated.
SIL is entered into a transponder ....


I’m not sure you are necessarily correct on that.

AIUI, for example, the TT31 self-configures SIL according to the protocols configured on the interfaces between it and the source device; there is no way to set it manually.

Interesting...
A Dynon Skyview integrated transponder which is a rebadged Trig TT21 on first installation will give a SIL=1 setting but you can manually adjust it in Dynon Skyview settings to SIL=0 which is what the LAA say it currently has to be on a Permit aircraft.
  • 1
  • 16
  • 17
  • 18
  • 19
  • 20
  • 29