PilotAware
British Forum => General Discussion => Topic started by: dimme on February 14, 2016, 11:53:38 pm
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So I was wondering why Mode A and C transponders are not supported?
Given that you have an on-board GPS unit, and you know the RSSI from other Mode A and C transponders, and given that the aircraft is moving through the air, localization should be possible even for Mode A and C transponders by using a simple free-space path loss propagation model (the air doesn't have many reflectors anyway).
Slides 10 and 11 present a simple solution: http://www.eit.lth.se/fileadmin/eit/courses/etin10/2014/LectureA3_Positioning.pdf
E.g. the RSSI for the last X known positions could be used to estimate a static position, and since the other airplanes are moving through the air the next position could be estimated by adding the newest sample and discarding the oldest one (rolling estimation). Kalman filtering could also be applied to get rid of most of the errors.
/Dimitrios
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There's beta software in the pipeline which does this.
Not much flying going on at the moment to give it a proper test though.
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Sign me up for it =)
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If there is Beta SW it is invisible to this forum.
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So you don't want a beta tester that has access to an airplane and is willing to fly it up for you?
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ModeS detection is working pretty well in the Engineering Prototype.
ModeA/C is proving a little more difficult, this is due to the slightly different way that ModeA/C is transmitted.
This leads to potential sampling errors when using Software Defined Radio.
This is not a simple problem to solve for various reasons.
Thx
Lee
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There are too many variable for this to be any use, if you ask me....
Results will be unreliable and possibly more useless than no result at all! :-)
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Nah, I think it's pretty good. But it should be easily turn-off-and-on-able, as an advert once said!
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How do you know it's any good?
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There are too many variable for this to be any use, if you ask me....
Results will be unreliable and possibly more useless than no result at all! :-)
Mode A and C detection is the only useful thing in Sweden if you are flying below FL300.
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I do take your point, believe me :-)
One of the major 'issues' (if you call it that) and criticisms of these type of systems is that if the data isn't spot on reliable without introducing pilot workload, then there is an argument that this is a negative safety benefit.
So you spot a ModeC return on your screen... instead of being confident of its location (like you would a mode s return), a proportion of pilot workload time is taken trying to verify the position of the Mode C return... when this was originally conceived one of the big things from feedback was that you need untainted pilot assistance to detect traffic WITHOUT increasing pilot workload.
Mode S returns are reliable and alarms can be created based upon accurate position data, which means that pilot workload is not hindered, more that the system is offering genuine assistance and only takes your attention when it really is required..
Adding into the mix an unreliable Mode C return and now the pilot has to take cockpit time to verify the accuracy of this information (very time consuming!). Now we have a system that is arguably not helping, more that it is increasing your workload with unreliable data.
Spend time trying to verify this and you may be victim of using a percentage of your workload time being unnecessarily distracted on something where there could be more important matters to be thinking about.
The naysayers would have a field day on this one..... Is this an assistance device where no pilot workload is used looking at the screen (which was what we were aiming at), or is it something which given a mode C return actually distracts you from what you should be doing?
It is important not to invent technology just for the sake of it "because we can".
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Adding into the mix an unreliable Mode C return and now the pilot has to take cockpit time to verify the accuracy of this information (very time consuming!).
That's not a valid argument really. If you're sitting there unaware of any other traffic, is it better than having an alert that there is other traffic around, say roughly within a quarter of a mile of you? Maybe Mode A is unhelpful, but Mode C/S will be useful, and is the basis of the Zaon MRX device and a few others which only give you a height an approximate range based on signal strength.
Now we have a system that is arguably not helping, more that it is increasing your workload with unreliable data.
There's a news item on the BBC at the moment about lions who have escaped from a national park and are wandering the streets of Nairobi. Would it be better to have a news alert that there are lions in your neighbourhood or is it unhelpful as you can't pinpoint where they are accurately and it may distract you from "more important" matters?
Spend time trying to verify this and you may be victim of using a percentage of your workload time being unnecessarily distracted on something where there could be more important matters to be thinking about.
What important matters?
It is important not to invent technology just for the sake of it "because we can".
Maybe, but this isn't it. It's the only feature which many admit would convince them to buy a PilotAware. It's a very useful addition which will warn of other squawking traffic who don't have ADS-B or another PilotAware.
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Hello Paul,
I'm not trying to be deliberately argumentative here, merely challenging the thought processes :-) From very early discussion about PAW, much of the feedback was "I don't want another bloody gadget that is going to distract me", which is after all a valid point of view... And to be fair, many of the gadgets we use can be quite a distraction.
The argument of being fixated on something which isn't actually a risk, while being completely oblivious to something else which is a significantly higher risk (i.e. "more important matters" - it could be anything) is a known attribute of human factors... it is also a well documented and understood psychology which is manipulated by illusionists and marketers alike!
I'm not saying one or the other is right or wrong (and I do accept that a Mode C detection scheme would be very useful).. what I'm saying is the system should not be designed to include more distractions leading to a loss in "improved" safety, over and above its main intention, which was to give a reliable and accurate traffic data feedback to the pilot - without increasing cockpit workload.
By the way I was looking for that bloody lion all morning.. couldn't find it... and didn't get any of my other work done which was %^&*£"$ urgent. Turned out the BBC got it wrong and it was actually Mr Miggins's cat seen through a telescope (they didn't mention that). I wish I would have known that, since I wasted my entire morning and could have been much more constructive doing something more important... ;-)
Rgds
Andy
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I see your point Wobblewing, but there are methods to verify the accuracy of an estimation. It doesn't have to be presented to the pilot unless let's say the estimation is within a 95% confidence interval.
Now I'm taking it to another level, but since radar locations are known, it is possible to listen on 1030 MHz for interrogation pulses to transponders with a second SDR and based on timing and geometry get a much more accurate position estimate of the aircraft.
There are technical solutions as long as there is a will!
EDIT: You can even run them on the same clock if you want thus maintaining phase coherence =)
http://www.rtl-sdr.com/passive-radar-dual-coherent-channel-rtl-sdr/
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Yes indeed. like I say not trying to kill it off, but like to add some practical angle :-) The naysayers would be worse, believe me :-)
I had thought about timing etc off the radar heads, but I'm not sure this would work because it's probably not possible to correlate the Mode C response to the radar interrogations?.. so you'd loose the timing reference in order to make the calculation... AFAIK Mode C doesn't have a field in its return transmission which describes the radar head it's responding to (unlike Mode S where reduction of "FRUIT" is one of the main advantages, so is more controlled by the radar head itself).
In any case the current PAW implementation uses the standard widely available DUMP1090 program to decode transponder squawks, so a "DUMP1030" would be required, including the associated algorithms etc. Not impossible, but quite an undertaking. in addition you need a lot of MIPS in the DSP to be able to discriminate very small difference in the arrival time of the received signals. Timing resolution could be a challenge, so perhaps not suitable for our low cost RPi solution.
An idea I thought of which might work is the use of multilateration, based on lots of ground based PAWs that could broadcast Mode C positions using a special format over the P3I channel. Each of these ground stations use GPS timing for triangulation of the mode C reception, they then coordinate the measurements to calculate position.. I could envisage a ground network broadcasting P3I based packets to airborne PAW systems, which could give a more reliable Mode C detection method..... It's one hell of a lot of effort though! I suppose you could take MLAT outputs from FR24 and broadcast on P3I.. only issue there is that FR24 adds too much delay, so we'd get the data too late!
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Hi All
This argument keeps appearing on this and other forums about the possibility of PAW (and other devices) generating false alerts that distract the pilot from other important tasks and the possibility that it increases rather than decreases pilot workload and may diminish peoples perception of its usefulness over time.
Now I have to confess to being a relatively newly qualified NPPL and find this hard to understand. I can vividly remember the syllabus for the NPPL in which every exercise has a sub-heading "Airmanship".
At the top of this section the very first item was "Lookout".
The whole idea behind the "Bearingless Mode a, c, s, Alerts" generated by PAW is to concentrate the mind on LOOKOUT, not to stare at the screen seeking information which is not going to be there.
Depending on your own settings in PAW and your navigation software you will be alerted to a target within +/- xxxx feet of your own altitude. The only clue to its distance will be the colour coding, Green, Amber, Red. If you then fail to obtain a visual on that target and it disappears without trace, no problem, if you do get a visual and it's no threat, again no problem, if you get a visual and need to take avoiding action, OK. In all of these situations PAW will have done its job. If you didn't get this warning whilst you were busy doing "something else important" as has been quoted and you encounter someone else also doing something other than "lookout" it could turn out to be the last warning you never get.
I've said it before and will say it again, there are no "False Alerts" generated by PAW (or other systems), it is telling you there is something in your vicinity that requires your attention and it's up to you what you do with that information. Ignore it at your and others peril.
If a few minutes of extra vigilant lookout is considered extra pilot workload then it's a burden we should all be prepared to carry.
Alan
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Very succinct, AlanG!
I agree with all you said.
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If you didn't get this warning whilst you were busy doing "something else important" as has been quoted and you encounter someone else also doing something other than "lookout" it could turn out to be the last warning you never get.
Spot on Alan,
A warning of an aircraft in the vicinity at a similar height has got to be good thing even without direction information.
It could help prioritize "lookout" at a critical moment.
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Ok I can take a hint :D
I know where I fly there will be mode C all over the place, so it'll be a case of lookout or lookout!
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I took the PAW out for a test in a PA28 and it picked up the ADS-B planes at about 10-15Nm with a stubby 1/4 wave aerial. We were advised of Military Helicopters operating at low level which we saw but as expected these do not currently show up in PAW. I see from the RAF's excellent AirClues online magazine Issue 14 that in an article which mentioned airprox and Class G "that many military aircraft are now equipped with TCAS and many others are being upgraded. All military aircraft squawk Mode3A/7001 with C when low flying and if they have a transponder use it with Mode3A/7000 Mode C selected to make themselves more detectable by TCAS-equipped aircraft" - and hopefuly by ourselves as the Mode A/C work comes to fruition.
Chris
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There needs to be a contact to equip all military aircraft with a PAW... :D
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There needs to be a contact to equip all military aircraft with a PAW... :D
I doubt they'd use it for the same reasons they generally don't carry ADS-B out.
Alan
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If you are watching for Ext Squit on say FR24, how do you tell if they are either Mode C, Mode S or ES returns ?
John
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If you are watching for Ext Squit on say FR24, how do you tell if they are either Mode C, Mode S or ES returns ?
John
The non Mode S are "MLAT" returns. MLAT stands for multilateration and they estimate these positions based on triangulation from all available ground stations.
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Rather non-ADS-B ones show up as MLAT if they have Mode S. If they don't have Mode S then you can't identify them so they don't appear. Maybe someone could suggest they show Mode C contacts as well, but just marked as Unknown. I don't know if the current FR24 receiving system is set up for Mode C.
As for military and ADS-B, some do have it, but they're blocked in FR24. You can see military aircraft on the PAW which don't show up on FR24.
Remember this was the RAF who painted their training fleet black to aid visibility. I suspect the RAF would be quite happy to try low cost means of preventing their multi million pound assets from hitting puddle jumpers.
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I found out that Royal Helicopter G-XXEB has ADSB when it flew directly over my house the other day. I was quite surprised at that.
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....I suspect the RAF would be quite happy to try low cost means of preventing their multi million pound assets from hitting puddle jumpers.
Mil need tough vibration performance, so while a good idea in concept it would struggle to meet their specs. Reference oscillator needs to be tolerant to high vibration, which is usually a fairly high cost item.
It would need to be ruggedised, but do-able of course.
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Not necessarily. If all that's too difficult they just Velcro something to the dashboard like they did with their Garmin GPS IIIs back in the day...
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Cool. Are they still flying the Tiger Moth?
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Sure! But they're also still flying their Hawks and C130s!
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I agree with Dimme about this. Some kind of implementation of mode A/C is crucial in Sweden. I think PAW wont be able to attract a general interest without it here.
If mode A/C is not implemented as a visual in the Flarm protocol it would still be great to have a list with known transponder broadcasts in a separate mobile app or something.
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Mode A and C detection is the only useful thing in Sweden if you are flying below FL300.
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