I wonder if it will be possible to determine (by in-flight testing) a band of received signal levels that are most likely to indicate a potential close encounter?
For example, is there likely to be much difference in received signal levels between an aircraft transmitting at 1, 2, 5 and 10 miles away? My thinking is that you could ignore Mode C signals until they got to a level typical of, say 2 miles away.
Yes, there will be all the PAW variables you mentioned but perhaps a good starting point to possibly refine upon as more data becomes available?
As all Mode C transponders are built and tested to certified levels (I assume they are?), and most installations use standard transponder antennas, I wonder if there is really a significant difference in transmitted power from different aircraft/installations?
Tony
Tony, that's what Lee has asked the 'engineering group' to help him with (though due to family commitments, weather and a back problem I've yet to contribute my share). We fully acknowledge the difficulty of determining accurate range to raw transponders solely from signal strength, especially given the many variables of transmission / reception as referred to by Paul above, but feel it's really important not to simply disregard such a large group of aircraft without giving the problem due investigation.
The counter argument is that you create too many false alerts, then people will no longer trust it. At least with PAW and Mode S you know if you get an alert then it's accurate.
The Zaon devices lost credibility pretty fast, for alerting to traffic that wasn't there or vice versa. So, people don't trust them. It actually creates MORE pilot workload, because now you have to actually take time to verify the alert, thereby diverting attention from what the pilot should be doing.. BAD! and goes against the ethos of a device that doesn't impair pilot workload and cockpit efficiency.
Wouldn't want PAW to be tarred with the same brush, by giving bad alerts.... the majority of alerts would come from ModeC and would be very unreliable. The PAW system would then very quickly gain a bad reputation.
Needs to be carefully considered, in my opinion :-)
Wobble wing,
I fully agree, which is why I volunteered to help Lee with the testing. As a long term ZAON MRX PCAS user, (since 2009 including trips abroad) I am fully aware of the issues.
Yes it does give alerts for which you can't find the aircraft - generally due to a CAT with it's higher power transponder, but these are not in reality 'false' alerts and once you get used to the system can be quickly disregarded.
My real worry is that without raw transponder detection, PAW users may get lulled into a false sense of security and allow lookout to become lax. Especially bearing in mind that GA traffic - which is what we are most at risk from - which wants to fly in controlled airspace will happily fit a transponder (lots already have), but are unlikely to go down the ADSB route unless it becomes easier /cheaper (viz. the recent uncertified ADSB trials and the potential for PAW to provide the 'uncertified' GPS source if this goes ahead).
As has been said earlier, until ALL GA and commercial helicopters (very unlikely) can be persuaded to adopt PAW, raw transponder detection is the best route we have to a very significant proportion of the aircraft likely to fly into us!
Please bear with us and let us give it a fair trial. If it can't be done to an acceptable level of reliability, I know Lee won't roll it out.
Best regards meantime
Peter
p.s. In my experience, When the ZAON 'fails' to alert me to a nearby aircraft, the most likely scenario is that it is NOT transponder equipped. Don't be too quick to 'blame' the ZAON - PAW won't 'see' aircraft not broadcasting any form of alert either!!
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