Primarily for general aviation discussion, but other aviation topics are also welcome.
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#1613177
The sky-gods who are carting a few hundred souls about, are , usually, flying well away from the "hobbyist" who makes up the bulk of GA.
It's reasonable to expect that those who pay for a professional transportation, actually get one and to that end, the equipment and aids ensure we have pretty good Commercial air transport.

It's totally unrealistic to expect the private pilot to maintain the same levels of equipment and the same level of training and currency-maintenance,as his Commercial oppo.
Hence you have the fragmented ,but pragmatic solutions to the lower-skilled, less- practised £100-hamburger-crowd bumping into each other or making too many laundry-visits.
We all know it's not a perfect scenario, but there seems to be a general consensus. - each has it's own niche.......Flarm does for gliders, what nothing else does. Uavionix appears to try to emulate the £2000 + bit of kit for ~ £600 , from what I understand, it is extremely good, but transmission- range limitations mean it's ...well, -limited ! Then you have the cheap as chips, PAW. AIUI, It's open-source, so, no proprietary system ransom....If you're a geek and want to tinker with it, it's all yours.
The inescapable fact is that Aviation is expensive at all levels. until the ultra-light deregulated market is well-established, even that totally unregulated regime is not open to the impoverished, as second-hand stuff is still a few thousand, older, tiny engines are probably a bit marginal and wings/lines /harnesses probably past their prime.....for these people, < £200 is affordable to shout "I'm here" to those who can "see" them. I don't think the Sky-God at FL umpty-umpt Knows about, or cares about the Paraglider a couple of miles below, chugging along at 30 Kts. OTOH, the once-a month in a Permit aircraft or elderly spam-can pilot really should take advantage of a" Maplin's explosion" keeping an electronic eye out for him, whilst shouting "watch out, i'm here" to anyone else prepared to pay ~£200 to see and be seen.

Local hangarage for a Flexwing is over £100 a month....If I were a pilot , i'd not hesitate to spend that 2 month's rent on my personal safety (or giving others fair warning to get out of my way :twisted:
#1613180
The daft thing is, Steve, that most of the airliners flying around at the moment may well have certified GPS and be able to guarantee the output of their position but the majority have no way of seeing other traffic, other than TCAS. There are very few airliners at the moment with ADSB In and, of course, TCAS does not use ADSB yet.

I appreciate that all this will eventually come but, as it stands, those certified units are great for telling oceanic controllers etc where we are but they do almost nothing for electronic conspicuity i.e. telling everybody else where we are.
#1613185
Straight Level wrote:@the geeks..... If I'm bimbling about, say between 1,000 and 5'000 FT and OCA, (or inside CA for that matter) what difference does it make to what I see or how others see me if I am SIL0, SIL1 or SILgoldplated?
Which aircraft sharing the airspace with me has equipment that will ignore SIL0?


No difference carry on. You are VFR OCA and that’s fine.

The only advantage SIL = 1 may have in the future is if it becomes acceptable to provide a crossing in Controlled Airspace with no other transponder outputs.
Straight Level liked this
#1613213
Whereas S&L is VFR OCA and all is fine, I think the answer to his question is that with SIL 0 only uncertified kit will be able to see him (assuming this GPS is being used for ADSB Out) whereas with 1 & 3 certified and uncertified kit will be able to see him.

Please correct me if I'm wrong because I'm also trying to get to grips with this stuff.
#1613220
PaulSS wrote:Whereas S&L is VFR OCA and all is fine, I think the answer to his question is that with SIL 0 only uncertified kit will be able to see him (assuming this GPS is being used for ADSB Out) whereas with 1 & 3 certified and uncertified kit will be able to see him.

Please correct me if I'm wrong because I'm also trying to get to grips with this stuff.


I think you have to careful here.

There are a number of devices that you can put into EASA Aircraft and there is the appropriate STC and the ability to connect to Certified GPS.

Have a look on the Mendelssohn Site for a start

These can see SIL and SDA = 0 and have "licensed the use of the TIS interface for Garmin products.

Some people might consider these to be "certified" and certainly FLARM has an STC for installation in EASA Aircraft.

{Geek Stuff Starts]
If you mean that Commercial Air Transport (CAT) using a Traffic Collision Avoidance Systems (TCAS) which provide more inclusive information to avoid conflicts then yes these are only looking at devices which indicate SIL and SDA = 1 and above.

So if you are flying on OCAS the SIL = 0 where CAT avoids flying, generally, then you will be seen. When you start entering controlled airspace with CAT then your dependant on separation by Radar and ATC and CAT with TCAS will not see you.
[Geek Stuff Stops}

Fly with the best you can afford and understand the limitations is the best advice I can give.
#1613221
PaulSS wrote:Whereas S&L is VFR OCA and all is fine, I think the answer to his question is that with SIL 0 only uncertified kit will be able to see him (assuming this GPS is being used for ADSB Out) whereas with 1 & 3 certified and uncertified kit will be able to see him.
Please correct me if I'm wrong because I'm also trying to get to grips with this stuff.


Paul, yes, that was second part of my question.
For example, a SR22 with certified bells and whistles ASDB running >=SIL1, will I appear on his display if my kit is SIL0

SL
#1613222
Straight Level wrote:
PaulSS wrote:Whereas S&L is VFR OCA and all is fine, I think the answer to his question is that with SIL 0 only uncertified kit will be able to see him (assuming this GPS is being used for ADSB Out) whereas with 1 & 3 certified and uncertified kit will be able to see him.
Please correct me if I'm wrong because I'm also trying to get to grips with this stuff.


Paul, yes, that was second part of my question.
For example, a SR22 with certified bells and whistles ASDB running >=SIL1, will I appear on his display if my kit is SIL0

SL


I'm not sure that the answer can be 100% yes given this is an internet chat room and we don't know the equipment fit in the SR22 but there is a 99.9 % possibility that the answer is yes a SIL = 0 device will be seen by your SR22 example. :)
Straight Level liked this
#1613230
gaznav wrote:...“Why aren't we raving about this?”. Because it hasn’t quite hit the nail on the head for many of us - the use of another proprietary signal standard, like FLARM, means that it just adds to another standard to detect by extant receivers like other ADS-B In, FLARM or PowerFLARM receivers. The internationally recognised standard of ADS-B is the way ahead and when, or if, PAW starts pushing out ADS-B we really will have something to “rave about”. :thumleft:


I may now really upset the apple cart :?

Firstly lets not confuse an international standard with CAP1391
Can devices which conform to CAP1391 be used outside of UK airspace - No, so how is this international ?

More importantly regarding ADSB on 1090Mhz using OOK (On/Off Keying), how much capacity is available in this spectrum some simple - back of a napkin analysis

ADSB/DF17 emits 4 packets per second
2 x Airborne Velocity
2 x Airborne Position
Each packet consists of a preamble (8uS) and the Data Block (112uS)
that is a total of (8 + 112) x 4 = 480uS every second
I am not great at Math so lets round that to 500uS for simplicity

In the most perfect of worlds, if all ADSB emitters could be synchronised then 2000 emitters could all run without ever corrupting each others data.
If that was a motorway, it would mean every car driving bumper to bumper without touching one another

The world is not ideal, these are not synchronised and so this will never be the case - which means they will stamp on each others broadcast time slot in a random and undefined manner.

This is further complicated, ADSB is not the only emitter on 1090Mhz, we also havethe following transponder transmissions :-
Mode-A (20uS)
Mode-C (20uS)
Mode-S (64uS)

Each of these transponders are interrogated by multiple ground based radar systems and air based TCAS systems, so these are NOT N-times per second, they are as many times per second that they are interrogated - now you start to see how congested the spectrum is.

Now consider the range of these transmissions, I can receive ADS-B transmissions from 200km away using PilotAware on the coaming. So imagine a geographical area with a radius of 200km all broadcasting simultaneously where any transmission can overlay any other transmission.

Usually we think that in RF transmission, the strongest signal wins over, which is great, I will only receive the strongest transmissions, which are closest in proximity right ?
Wrong, On/Off Keying does not work like this, it is a CARRIER-ON / CARRIER-OFF method so data corruption occurs very easily with overlapping transmissions, this is not the same as FSK which is a method that uses a 2 symbol carrier FREQ-1 / FREQ-2, importantly, a FREQ is always present, and never silent

Nobody has done any detailed analysis to know what the system break point is - but the FAA did envisage this was a problem and have encouraged ADS-B/1090(OOK) for aircraft flying above FL180 and UAT/978(FSK) for aircraft flying below FL180. proactively addressing any possible congestion issue.

So to the question
gaznav wrote:...or if, PAW starts pushing out ADS-B we really will have something to “rave about”. :thumleft:

Hmm, well how about, if those encouraging usage of this spectrum, in the manner specified were to indemnify the manufacturers and end users, that should the system fail and need to be retracted - all costs and investment would be compensated.
If the capacity of the system is as robust as those who promote it, then this is perfectly reasonable, as this is a zero cost sum - right ?

Who wants to volunteer first ?

Thx
Lee
T67M, Keith Vinning liked this
#1613236
leemoore1966 wrote:
I may now really upset the apple cart :?

Who wants to volunteer first ?

Thx
Lee


Ok I'll bite but I cannot publish my thoughts and answers because of confidences from my past, any way it would take the geek mode off the page :-)

If the maths were that simple :-)

What your describing is Fruit and Garble.

Ground Based Receivers and Extractors as well as this used in TCAS are a little more complex in their front end design to address the issues as well as changes being made in the interrogate frequencies and therefore reduction in replies required to determine a SSR position.

A software tuned receiver is not even close to the same level of firmware in the decoding process.

Can any one guarantee - no.

Even Safety Management is predicated on predicted levels of failures and modes and suitable mitigation applied - it does not preclude "Sods Law".
#1613252
PB wrote:We (I) am not raving about it because:

• It's essentially a solution searching for a problem. The statistical chance of a mid-air collision is (vanishingly) low and very small compared to all the other ways people choose to do themselves harm in light aircraft.


That's simply not the case. When I asked for the European data on this from EASA, it turned out that 5% of fatal accidents (54 of 1107 over an 8 year period) were mid-airs. Since you often lose more than one aircraft in a mid-air, that's 5-10% of the aircraft involved in fatal accidents. It is not the most significant cause of fatalities in GA, which remains loss of control in flight, but there is no way that 54 fatal accidents can be described as "vanishingly small".
#1613256
I apologise for descending in to Geek Mode for those who are genuinely looking for answers but are lost with the many acronyms and technicalities.

There are many technical issues surrounding the use of 1090 MHz, but sometime, just sometime, these are mis-interpreted or misunderstood and should not detract from the healthy debate about what one should be buying/using etc.

I repeat what I said before, "I believe you should chose the device you can afford and understand what it will, and will not do, and look out of the window.
gaznav liked this
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