Ads-b and sailplanes

On Monday, April 6, 2015 at 11:36:33 AM UTC-7, wrote:

Sorry, FLARM is not an "anti-collision" system like TCAS, it is a "traffic advisory" system like ADS-B. The only thing that FLARM-specific algorithms do is reduce the number of warnings provided of nearby gliders that are determined not to be on conflicting paths. Having identical firmware in all FLARM units simplifies the programming issues and allows for use of lower-powered processors. Implementing similar algorithms on top of the more diverse ADS-B environment will not have any innate tendency towards making matters worse.


I'll explain.

After talking to the Flarm engineers, I concluded that you need to have a more nuanced view than "anti-collision" and "traffic advisory". The middle ground is what Flarm does and ADS-B does not. Call it "collision advisory" then. It tells the pilot not only is there an aircraft within some airspace volume around him, but does it have a trajectory (forecasted out some tens of seconds and based on knowledge of what type of aircraft it is) that has a reasonable probability of intersecting his aircraft's trajectory. It then displays quadrant and altitude differential for the pilot to act on (TCAS additionally tells the pilot what to do, that is true, but it doesn't fly the airplane, so the pilot is still in the loop for collision avoidance). Collision advisory like Flarm must account not only for filtering threats from non-threats, but also how pilots are likely to respond to how the threat is presented. Flarm uses a particular convention, but others are possible - all the way up to TCAS-type RAs.

The filtering of collision threat versus non-threats in a glider scenario is the entire difference in suitability between Flarm and ADS-B. Trying to do this kind of filtering without a position forecasting algorithm is challenging because you can't effectively filter threats from non-threats. Without a common position forecasting algorithm across all systems you might have one system give collision advisories based one one set of assumptions and another system issuing advisories on another set of assumptions and could lead to "you zig, I zag" kinds of asymmetric warnings and pilot reactions.

Consistent warning algorithm and advisory display results in better (but not perfect) pilot response to collision advisories. Think about a head-to-head approach. It's hard enough for pilots to deal with Flarm today (turn left? turn right? climb? dive?) but it can get worse if the warnings come at significantly different times (or not at all) and with different philosophies of what to display. Consistent position forecasting and consistent display of the threat are critical to pilots taking successful and non-conflicting action to avoid a collision.

To illustrate - Imagine three different (ADS-B-based) systems on three different gliders in a thermal - one forecasts turning and uses total energy based on received GPS position and trends (this is not as effective or reliable as doing what Flarm does by forecasting future position prior to transmission, but leave that aside for now), another algorithm does a straight extrapolation of the current instantaneous velocity vector and a third is position only. Imagine the first system also gives you an indication of where the threat will be relative to you when it is expected to be at closest approach so you can steer away from that point and the second just tells you when either gilder is pointed at the other and indicates where to look to pick it up. The third one will give you advisories continuously as long as any other glider is within a thousand feet of you or so (my LX 9000 does this, but only once when it picks up a new target. Even so, I want to turn it off most of the time). In a crowded thermal these three different approaches to collision threat filtering and display could - with pilots in the loop and reacting - create all kinds of chaos that I would think of as making matters worse.

That's why I conclude not having a single collision advisory algorithm and display philosophy could make matters worse. I wonder if this is why ADS-B systems are pretty conservative about what they tell the pilots about traffic vs collision threats.

Andy

On Monday, April 6, 2015 at 3:00:05 PM UTC-7, George Haeh wrote:
Before PowerFlarm, I had two close encounters with airliner turboprops in
Class E airspace. At my old club I took a photo of a close encounter
between an airline turboprop and a towplane pulling a glider below 2000
AGL.

With PowerFlarm, I spot their ADS-B returns 10+ miles away. Very easy to
stay well out of their way.

Air Avionics has a project website ads-b.de with a European outlook (Google
translate recommended if your German is challenged).

A Dutch website discussed using PowerFlarm for GPS input to a transponder,
but non-GPS data has to be filtered out. Can't find that webpage any more,
but filtered PF GPS data looks like a good way to go.

In pre-PCAS flying days I had an eye-opener: I was a few thousand feet AGL about 5 miles south of the Panoche VOR in California. I was working a weak thermal in my DG-303, lots of small scraggly excuses for cumulus in the area. I take a turn and as I'm coming around a Cessna 152 cuts right through my thermal circle just above me. *Wholly Crap* I pushed the nose down, they fly on off into the distance not flintching at all, I don't expect they ever saw me. They had 2 POB, I suspect a student under a hood flying a radial the Panoche VOR. I was trying to look out and all I can think is that Cessna was sitting against the background of those scraggly clouds and just very hard to see.

I ordered a Zaon PCAS after that and got one of the first ones available, an old grey unit. That easily earned it's keep.

Multiple times, especially when retuning the local busy GA airport the PCAS would give useful warnings of GA aircraft. And we sometimes had issue in the area with poor quality radio calls/position reports, sometime just due to inexperienced student pilots using that airport as an early cross country destination.

On another occasion my PCAS was going nuts and I kept looking around and could not see anybody and it just stayed a constant range (close) and warning 1,000 foot or so above and then started to get lower. Kind of a useful indication that even when you are looking you can't necessarily see them (and to trust the PCAS that something is out there). Then I spot this crazy aircraft a Thrush or similar equipped for something interesting, covered in antennas. That was orbiting right above me and slowly descending to look at me.. Maybe he was just curious, kind of annoyed me, and to this day I wonder what the aircraft was rigged up for.

OK, here is my PCAS story, then a comment for Mike:

Couple of weeks ago, flying down to Ardmore OK to pick up our new towplane, I'm riding right seat in a nice RV-6. VFR on top, squawking 1200, pilot is messing around with a radio, and I'm playing with my trusty PCAS (I NEVER fly without it). Odd, it shows our 1200 code, but shows us at FL024 (we were at about 9600ft). Tried this several times, same result. Then I lood across cockpit and at 10 I see a BIG CLOSE AIRPLANE!!, about a mile away on a collision course. I could see the top of the cabin so we were probably 100 above it, but it sure looked impressive! I yelled "AIRPLANE - PULL UP!" and we bumped up a hundred feet or so as it passed underneath us, apparently unconcerned.

Now, what we figured happened is: 1. Our transponder was stuck putting out a bad altitude (2400ft) instead of the actual pressure alt (about 9400ft). 2. My PCAS was telling me that - but I didn't connect the dots. And 3. since we were putting out our altitude as 2400 ft, the airliners (I think it was an Airbus 319) didn't get a TCAS warning, and we didn't get a PCAS warning (since it thought we we low and the airliner high above the threat bubble!)

Would have made an interesting NTSB report if we had entered that Airbus's cockpit via the windshield.

We cycled the transponder several times and it started to show the correct altitude, which is when the lightbulb came on....

So - PCAS is a wonderful thing. PowerFLARM (which has PCAS + 1090ES ADS-B in + flarm) is even better. But you still have to look out the window!

Oh, and Mike? Your club sounds like mine - bunch of ignorant cheap *******s flying beat-up old gliders, and who think a Macready ring on a Winter vario is a trick flight computer. Out of the 20 some club and private gliders on our field, 2 have PF, 2 have transponders, and the rest barely have audio varios. I really think it's a cultural thing (glassholes & racers vs the rest). But your argument against PF and for ADS-B is bogus, since YOU STILL HAVE TO HAVE A MODE A/C OR S TRANSPONDER WITH YOUR MAGIC UAT ADS-B OUT BOX! Will you please explain to me how you can get away with a UAT-only solution in a glider? And how will it help you see everyone else out there?

Kirk
66
Zaon MRX PCAS and PowerFLARM brick.

On Monday, April 6, 2015 at 12:15:02 PM UTC-7, Mike Schumann wrote:

Blaming me and other pilots who are trying to educate the glider community on what their options are for the disappointing sales of POWERFLARM is ridiculous. The reason a lot of people aren't buying POWERFLARM units is that they perceive this to be a half baked solution for areas near major metropolitan airports, where a significant collision threat is non-glider traffic.

I suspect that if POWERFLARM got their act together and fully supported the FAA's ADS-B architecture, pilots like me would have whole different attitude. With that kind of product the MN Soaring Club might even become a customer.

Flarm is installed in something like 75% of the active glider fleet worldwide as of a couple of years ago so I'd be hard-pressed to call it a disappointment. It got most of that without any ADS-B In capability. The US adoption has been slower, but there are a number of reasons that probably don't auger well for those gliders going being equipped with ADS-B either - such as relatively large fleet of older gliders without electrics, a different philosophy for non-privately owned gliders (rides and training) and a number that are in more remote locations with no urgent perceived need for much of anything.

I think it misreads the situation in the US to conclude that people are holding off buying PowerFLARM because they are chomping at the bit to put $5-6000 worth of ADS-B kit into their $6-7000 glider.

Would it be better if Flarm had implemented dual-mode UAT and 1090ES In? Possibly at the margin, but the cost of PF versus the original Flarm is already much higher and that variant would only be useful in the brain-dead US ADS-B environment.

Before doing anything I'd recommend the Flarm guys take a hard look at how much UAT gets adopted versus 1090 ES in the US. There is a decent probability that UAT Out will have lower than predicted adoption as the benefits of Mode S + 1090ES Out become more apparent in terms of cost, simplicity and installation. Most non-gliders Carrying ADS-B In will be carrying 1090ES or dual mode In anyway so putting a (hopefully) cheap GPS on a Mode S transponder will get you seen by traffic. Given the relative speed differences it will be a lot easier for them to avoid you than for you to get out of their way anyway.

Andy

On Monday, April 6, 2015 at 3:39:17 PM UTC-7, Andy Blackburn wrote:
The filtering of collision threat versus non-threats in a glider scenario is the entire difference in suitability between Flarm and ADS-B. Trying to do this kind of filtering without a position forecasting algorithm is challenging because you can't effectively filter threats from non-threats. Without a common position forecasting algorithm across all systems you might have one system give collision advisories based one one set of assumptions and another system issuing advisories on another set of assumptions and could lead to "you zig, I zag" kinds of asymmetric warnings and pilot reactions.

I'll explain my (over-simplified and and I'm open to accept wrong) view. Flarm and ADS-B start out with the same source data, a position and velocity vector obtained from GPS. The primary difference is that Flarm calculates a forecasted trajectory (I've never looked at the details, but I wouldn't be surprised if it's more of a probable trajectory sphere at some time t+x) from the raw data, ADS-B simply transmits the raw position and velocity vector. The great advantage of the Flarm approach is that all it need do is intersect all of the received trajectories (or spheres) with the calculated trajectory for your own glider, which is great if you need to do it on an 8 bit processor. A lot more computation is required to accomplish the same thing with received ADS-B data, as the trajectory calculations need to be performed for all received targets likely to be a threat. That is not impossible, it just takes a lot more computational power in your glider, but we live in the age of low power consumption 64 bit processors that cost a USD or two in reasonable quantities.

The fact that all Flarm devices calculate threats in the same way is helpful, but in the end, it has no control over what any of the pilots involved do to avoid a collision, whereas with TCAS-II, the pilots most certainly should do exactly what their device calls for. I don't know if Flarm transmits data more frequently than the once per second slots I believe are allocated for ADS-B, perhaps someone else knows. Beyond that, however, I see nothing preventing anyone from taking the received data, filtering out the more distant targets, and applying target type (including glider) specific trajectory calculations to more intelligently provide traffic advisories. If someone has facts that suggest otherwise, I'm interested in hearing them.

I think the important thing to keep in mind is that gliders probably won't be exempt from the ADS-B (or transponder) mandate in the US forever. Boeing, Amazon, Google, and the rest of the US drone industry will eventually figure out (if they haven't already) that the easy solution for their problems is to lobby hard for all aircraft in US airspace to be ADS-B out equipped.. We don't have that kind of clout, nor does AOPA or EAA.

Marc

On Monday, April 6, 2015 at 5:12:01 PM UTC-4, Darryl Ramm wrote:
On 4/6/15 12:15 PM, Mike Schumann wrote:
On Monday, April 6, 2015 at 3:35:11 AM UTC-4, Darryl Ramm wrote:
On 4/5/15 7:11 PM, Mike Schumann wrote:
On Sunday, April 5, 2015 at 4:45:31 AM UTC-4, wrote:
Amazing how big a mess the FAA has made of the ADS-B thing isn't it? It seems like it had the potential to streamline things and provide useful situational awareness about other traffic with a relatively simple and inexpensive device - sort of a like a universal implementation of FLARM-like technology in all aircraft. So much for that.

My club held off on FLARM for a couple of years as some members thought that ADS-B would make it redundant. We're now installing it to club ships and the tow planes as funds allow and many of the privately owned gliders have it. In my case all it took was one flight to be convinced of the usefulness of FLARM and I was a bit skeptical of its value in our location at first.

I wouldn't ignore ADS-B as the long term solution to the collision avoidance puzzle. It's almost inevitable that this technology will be the cornerstone of collision avoidance for UAVs that are going to start sharing our US airspace.

The confusion of having two standards (1090ES and UAT) is unfortunate.. The FAA (and originally MITRE, which developed the UAT standard) had good intentions. UAT provided the bandwidth needed for the kind of system that would permit a proliferation of other new services far into the future. Conversely adding 1090ES to the Mode S transponder standards provided such limited bandwidth to support ADS-B that there was legitimate concern that this technology would not work in some of the high density US airspaces (NYC, Atlanta, and Chicago), if all commercial and GA aircraft were so equipped..

Standardization on UAT would have been the ideal solution. Unfortunately this did not happen due to the lack of availability of a common frequency thru-out the world and the reluctance of the international aviation community to support this standard. If the FAA had insisted on UAT as the North American standard, it would have dramatically simplified the whole system at the cost of requiring dual equipage on a relatively small number of airliners used on international routes.

For most GA and commercial aircraft, operating within range of ADS-B ground stations, the current mixed UAT / 1090ES environment works well. The big issue is the lack of reliable ADS-B ground station coverage for low altitude operations in remote areas.

However, even in these environments, the future looks promising. There are now low cost dual frequency ADS-B IN receivers on the market that receive both 1090ES and UAT signals. Within the next year or two, single band ADS-B receivers will probably disappear from the market, due to the low cost of the much superior dual band receivers.

The big question is whether POWERFLARM will evolve to fully support this emerging ADS-B environment by incorporating a dual band ADS-B receiver and/or supporting the ADS-B ground station TIS-B capability, or if it will become irrelevant by the introduction of new low cost ADS-B IN solutions designed for the much larger GA community, incorporating not only dual band receivers, but also more sophisticated collision avoidance algorithms that take into account non-typical GA traffic like gliders, parachutists, and balloons.


The problem described not a few posts ago was how misinformed, and just
plain wrong, people had helped delay the introduction of PowerFLARM to a
location where it sounds like it could have been useful/wanted. And
those folks did that by harping on ADS-B,... let me guess influenced by
all that Bernald Smith/Miter/UAT pipe dream crap that too many folks
listened to including yourself. But don't let that stop you, and all the
previous harm done, keep on coming back, keep on telling people there is
something just around the corner...

---

So where is it again you fly? What glider do you own and what ADS-B
avionics have you been flying with? For how long? How long have you been
flying with a transponder? And how much practical experience do you have
flying with FLARM? All questions I've asked of you for before and you
never answer. So let me take a stab at that whole situation and if I get
any of this wrong I apologize and feel free to correct me...

You are a member of the Minnesota Soaring Club, you don't own your own
glider, you don't fly cross country much, you never fly competitions,
and you don't own or fly with a PowerFLARM or ADS-B Out? Is that right?
Just trying to judge your background for all the stuff you post about.
And from a technology viewpoint maybe you could let us know what
experience you have with high-technology, electronics, avionics, or say
actually getting any technology product to market?

You've been on r.a.s many times describing what seems like a dangerous
environment with lots of GA traffic where you fly and why gliders in
that environment apparently urgently need ADS-B equipment. And lots of
us have been baffled about why FLARM never seem appreciated by you since
it seems at times you might also fly with other gliders and/or towplanes
especially if operating from a club/gliderport. I've also asked you
several times where exactly you fly and you never answered. So let me
try there as well, again sorry for any mistakes and feel free to correct
any errors.

I believe you fly with the Minnesota Soaring Club, operating out of
Stanton Airfield. So based on all your past r.a.s posts you seem to
have serious concerns about (mostly GA) mid-air collision risks in that
location. Given those risks I would hope you have convinced the
Minnesota Soaring Club to at least equip their gliders with transponders
so at least ATC can easily see them if they fly within SSR radar
coverage and any PCAS, TCAD and TCAS equipped traffic also have a chance
to detect them as well. That would seem a prudent thing to do for any
glider club operating in what sounds from your past posts to be a high
traffic/high risk-environment. So I have to admit I was a little
surprised when I noticed that you had described to the SSA Executive
Committee back in 2011 that none of the Minnesota Soaring Club Gliders
were transponder equipped. I'm just going by your concerns you have
raised publicly, but in the four years since your comments to the SSA
has the club since corrected this apparent safety problem by installed
transponders and/or ADS-B Out in its glider fleet? Maybe you could give
everybody here an update about your mid-air collision concerns with the
Minnesota Soaring Club?

You are correct. I am a member of the MN Soaring Club. I don't fly competitions. We operate out of Stanton Airfield, which is just inside the Twin Cities Mode C veil.

None of our club ships and most private gliders at Stanton are neither FLARM, Transponder, nor ADS-B equipped. The reason for that is that most of our pilots are not willing to invest in partial solutions that we think will become obsolete in the next couple of years, as lower cost ADS-B options become available.

As far as my background goes, I was extensively involved with MITRE a number of years ago in their attempt to demonstrate to the FAA the performance capabilities of their low cost UAT ADS-B technology. All the testing was a success. The problem, which continues to this day, is that the FAA has dug in their heels on authorizing low cost consumer grade GPS chip sets for ADS-B OUT applications in VFR GA aircraft. My personal feeling is that eventually the FAA is going to cave on this issue, or they are going to be forced to subsidize a certified chip set that meets their specs. Otherwise, the political pressure from AOPA is going to become unsustainable as 2020 approaches.

As far as FLARM goes, a number of us were quite excited about this technology when it was first introduced in Europe, before the ADS-B bandwagon started rolling here in the US. Unfortunately, FLARM specifically prohibited the use of this technology in the US. One reason was that the European FLARM frequency was unavailable in the US. A bigger reason seemed to be the unwillingness of FLARM to expose themselves to the litigious US product liability environment, which is certainly understandable.

A number of years ago FLARM apparently had a change of heart, resulting in the introduction of the POWERFLARM product. The problem that I, and numerous other glider pilots have with POWERFLARM is the half baked implementation of ADS-B support, which significantly limits its usefulness in identifying non-glider based threats. TIS-B support would have been a huge feature, as this would immediately make all existing transponder equipped aircraft visible.

Unfortunately, the FLARM team did not want to bother with TIS-B. I assume that one reason is that they though this would be a temporary technology, which would become redundant in 2020 when most aircraft will be ADS-B out equipped. Unfortunately, the FLARM team didn't take into account that there are going to be UAT equipped aircraft that will be invisible without the TIS-B function. One work around would be incorporating a dual frequency ADS-B receiver so that POWERFLARM can see both UAT and 1090ES equipped aircraft. That approach is actually technically better than TIS-B in remote rural areas where aircraft are out of range of ADS-B ground stations.

Blaming me and other pilots who are trying to educate the glider community on what their options are for the disappointing sales of POWERFLARM is ridiculous. The reason a lot of people aren't buying POWERFLARM units is that they perceive this to be a half baked solution for areas near major metropolitan airports, where a significant collision threat is non-glider traffic.

I suspect that if POWERFLARM got their act together and fully supported the FAA's ADS-B architecture, pilots like me would have whole different attitude. With that kind of product the MN Soaring Club might even become a customer.


Thanks for the info.

TIS-B won't work without ADS-B Out, as you know. And in certified
aircraft, including any glider used for training you know that is a
multi-$k cost, and eventually TIS-B will go away, whether there are
affordable systems that could be usable in glider before then is an open
question. Meanwhile PCAS provides many PowerFLARM owners with useful
help for purely transponder equipped traffic, but with usual PCAS
limitations. And for compatibly with PCAS/TCAD/TCAS II then you need a
transponder anyhow. So I do not get why any club flying in what you keep
describing as such a high-risk environment would keep putting off
adopting transponders. Seems a bit of liability exposure, maybe one I'd
might have been careful about talking about publicly, but I appreciate
you being willing to publicly share your safety concerns about the
Minnesota Soaring Club operations. Especially since most of us just have
not been able to fathom the apparently unique situation, where other
clubs and owners have been willing/able to adopt PowerFLARM and/or
transponders as a best-available solution for their needs.

So the Minnesota Soaring Club is making what seems like (from your
description) critical safety decisions based on the hope that things
will change and an ADS-B solution will appear? Do they have a timeline
when they expect that to happen? Is there a time for when they will
revisit fitting currently available transponder technology to help
reduce the collision risk in this dangerous high-traffic area? Does the
FAA organizations in the local area and local GA pilots know of the
clubs mid-air collision risk concerns? And that most of the gliders are
not transponder equipped? Any joint-work on how to minimize those risks?

In high traffic areas (including GA) in the CA/NV area the local FAA
folks have been very encouraging/welcoming of adoption of transponders,
and have been really good at working together with the glider community.

Equipping a glider with a transponder will help protect you from airliners that are TCAS equipped. It won't help protect you from your average Cessna that is flying around recreationally, which in our environment is the most significant threat (as well as other gliders). Having a transponder doesn't help your personal situational awareness.

There are a number of very affordable ADS-B IN systems out there that give you great situational awareness today, IF you are ADS-B OUT equipped and within range of an ADS-B ground station. Granted, it won't come close to the functionality that FLARM provides in providing traffic advisories for gliders that are sharing thermals. That's important for competition pilots. Most recreational glider pilots are primarily interested in getting an overview of what A/C are in the area. If I get into an area where there are numerous A/C which I can keep track of visually, I find myself another thermal and stay out of everyone's way.

The reality is that ADS-B is the long term future foundation of the US airspace system. Claiming that it is "crap" is absurd. As glider pilots, we should be working on systems that are tuned to the specific needs of the glider community, but also fit into the overall ADS-B architecture. UAT is, for better or worse, part of this environment, and in the long run any solution worth buying needs to be able to handle this type of traffic.

The BIG problem right now is the cost of ADS-B OUT solutions. Technically, there is no reason that these systems can be as economical as currently available ADS-B IN systems. The entire price premium is a result of the FAA's absurd gold plated specs and certification requirements that are totally inappropriate for VFR aircraft (both gliders and piston powered A/C).

ADS-B OUT solutions for GA applications have finally started shipping, and prices are starting to come down significantly. Glider pilots, like their GA counterparts are to a large degree holding out, waiting for prices to come down. How long people wait to equip is going to be a function of price and capability.

My gut instinct is that we are going to see another slug of very interesting ADS-B products introduced at Oshkosh this year. I wouldn't be surprised to see Trig introduce a new version of their popular transponders with integrated GPS sources for a turnkey ADS-B OUT solution. As prices come down, more people will bite the bullet and make the investment.

The big question for the glider community is whether people will buy a POWERFLARM product that incorporates a half baked ADS-B implementation, of if they will just buy a low cost ADS-B IN receiver and couple it to an iPhone or iPAD running a navigation app. If the POWERFLARM community would quit bashing ADS-B and instead upgrade the product to handle both UAT and 1090ES traffic, there are a lot of people (me included) who might be interested in making the investment.

On Monday, April 6, 2015 at 6:37:14 PM UTC-7, wrote:
On Monday, April 6, 2015 at 3:39:17 PM UTC-7, Andy Blackburn wrote:
The filtering of collision threat versus non-threats in a glider scenario is the entire difference in suitability between Flarm and ADS-B. Trying to do this kind of filtering without a position forecasting algorithm is challenging because you can't effectively filter threats from non-threats. Without a common position forecasting algorithm across all systems you might have one system give collision advisories based one one set of assumptions and another system issuing advisories on another set of assumptions and could lead to "you zig, I zag" kinds of asymmetric warnings and pilot reactions.

I'll explain my (over-simplified and and I'm open to accept wrong) view. Flarm and ADS-B start out with the same source data, a position and velocity vector obtained from GPS. The primary difference is that Flarm calculates a forecasted trajectory (I've never looked at the details, but I wouldn't be surprised if it's more of a probable trajectory sphere at some time t+x) from the raw data, ADS-B simply transmits the raw position and velocity vector. The great advantage of the Flarm approach is that all it need do is intersect all of the received trajectories (or spheres) with the calculated trajectory for your own glider, which is great if you need to do it on an 8 bit processor. A lot more computation is required to accomplish the same thing with received ADS-B data, as the trajectory calculations need to be performed for all received targets likely to be a threat. That is not impossible, it just takes a lot more computational power in your glider, but we live in the age of low power consumption 64 bit processors that cost a USD or two in reasonable quantities.

The fact that all Flarm devices calculate threats in the same way is helpful, but in the end, it has no control over what any of the pilots involved do to avoid a collision, whereas with TCAS-II, the pilots most certainly should do exactly what their device calls for. I don't know if Flarm transmits data more frequently than the once per second slots I believe are allocated for ADS-B, perhaps someone else knows. Beyond that, however, I see nothing preventing anyone from taking the received data, filtering out the more distant targets, and applying target type (including glider) specific trajectory calculations to more intelligently provide traffic advisories. If someone has facts that suggest otherwise, I'm interested in hearing them.

I think the important thing to keep in mind is that gliders probably won't be exempt from the ADS-B (or transponder) mandate in the US forever. Boeing, Amazon, Google, and the rest of the US drone industry will eventually figure out (if they haven't already) that the easy solution for their problems is to lobby hard for all aircraft in US airspace to be ADS-B out equipped. We don't have that kind of clout, nor does AOPA or EAA.

Marc

Yes.

There are a couple of additional consideration on prediction pre- versus post- transmission. First, which is which is more robust in the event of lost packets, which happens pretty regularly with RF transmissions. Second, while both Flarm and ADS-B transmit at once per second, the inherent lag associated with post- versus pre- processing apparently works in the favor of Flarm in highly dynamic situations like thermalling. Add to that the lag associated with whether the traffic is ADS-B direct or ADS-R which increases the uncertainty of any predicted probabilistic position bubble and you can start to see why using ADS-B for common glider scenarios could easily devolve into a cloud of false alarms which, if the lags get close to the human reaction time of ~300 milliseconds (plus whatever dynamic response time constants of the gliders are), could melt down the prediction-reaction dynamic loop entirely.

I know less about the politics of it - whatever goes on drones will need to be cheap, cheap, cheap, and possibly lower power and range to keep the aggregate bandwidth requirements down (especially if Amazon gets their way). Flarm may have a leg up on ADS-B on both counts, but the FAA would need to agree and counting on the FAA to do sensible things would.

Andy

On Monday, April 6, 2015 at 11:17:14 PM UTC-5, Mike Schumann wrote:

Equipping a glider with a transponder will help protect you from airliners that are TCAS equipped. It won't help protect you from your average Cessna that is flying around recreationally, which in our environment is the most significant threat (as well as other gliders). Having a transponder doesn't help your personal situational awareness.


PowerFLARM, on the other hand, DOES (right now, today, in my glider) help protect me from not only other Flarm-equipped gliders, but also from airliners (by showing their 1090ES position) and from those "average Cessna"s carrying a Mode A/C/S transponder. These all show up on my PF display, on my Oudie map, and on my SN10. And since certified airplanes will need BOTH an functioning transponder and some form of ADS-B Out, the chance of someone out there with ONLY a UAT ADS-B Out system is remote.

There are a number of very affordable ADS-B IN systems out there that give you great situational awareness today, IF you are ADS-B OUT equipped and within range of an ADS-B ground station. Granted, it won't come close to the functionality that FLARM provides in providing traffic advisories for gliders that are sharing thermals. That's important for competition pilots. Most recreational glider pilots are primarily interested in getting an overview of what A/C are in the area. If I get into an area where there are numerous A/C which I can keep track of visually, I find myself another thermal and stay out of everyone's way.

So please describe for me a specific setup of hardware that you can put in your glider, today, to do what you describe above. In your certified training glider. Sure, ADS-B IN is cheap; but without the OUT you are getting what you paid for! Old weather and maybe, some partial traffic. Now, how are you going to get the OUT into your glider? And where are you going to display all the magic traffic info you might get (if you are close enough to a ground station, etc..). In my experimental glider, I can try a Trig/PF lashup, but why bother? A Mode S transponder and a PowerFLARM gives me everything I need, NOW.


The reality is that ADS-B is the long term future foundation of the US airspace system. Claiming that it is "crap" is absurd. As glider pilots, we should be working on systems that are tuned to the specific needs of the glider community, but also fit into the overall ADS-B architecture. UAT is, for better or worse, part of this environment, and in the long run any solution worth buying needs to be able to handle this type of traffic.


ADS-B, yes, but the UAT part is the "crap", as currently implemented. If the FAA and Mitre (or whoever) had come up with a $500 portable UAT IN/OUT with a display, that you could stick on your panel like a PF portable and start seeing all traffic around you (mode A/C/S/ES/UAT) - that would be great.. But that, obviously, didn't happen!

The BIG problem right now is the cost of ADS-B OUT solutions. Technically, there is no reason that these systems can be as economical as currently available ADS-B IN systems. The entire price premium is a result of the FAA's absurd gold plated specs and certification requirements that are totally inappropriate for VFR aircraft (both gliders and piston powered A/C).


Totally agree.

ADS-B OUT solutions for GA applications have finally started shipping, and prices are starting to come down significantly. Glider pilots, like their GA counterparts are to a large degree holding out, waiting for prices to come down. How long people wait to equip is going to be a function of price and capability.


Yes, for example, the Navworx PADS-B looks interesting - but again, only for Experimental aircraft. The cost of any ADS-B Out setup in a certified glider is still going to be high.

My gut instinct is that we are going to see another slug of very interesting ADS-B products introduced at Oshkosh this year. I wouldn't be surprised to see Trig introduce a new version of their popular transponders with integrated GPS sources for a turnkey ADS-B OUT solution. As prices come down, more people will bite the bullet and make the investment.

Are these the same people who don't have transponders now? I hope so, because then I'll see them on my PF!

The big question for the glider community is whether people will buy a POWERFLARM product that incorporates a half baked ADS-B implementation, of if they will just buy a low cost ADS-B IN receiver and couple it to an iPhone or iPAD running a navigation app. If the POWERFLARM community would quit bashing ADS-B and instead upgrade the product to handle both UAT and 1090ES traffic, there are a lot of people (me included) who might be interested in making the investment.

Back at you: if the ADS-B Community would quit bashing PowerFLARM (which exists and works) and encouraging people to wait for some future ADS-B magicware, perhaps more gliders would be enjoying the protection that PF provides TODAY, while waiting to see what the future actually brings.

Kirk
66

On Wednesday, March 25, 2015 at 6:15:44 PM UTC-4, Andrew Ainslie wrote:
Has anyone been following the latest moves from the FAA on ads-b and experimental aircraft? A recent article in flying suggested that they are going to relax the requirements for experimental planes so they need a GPS source that is equivalent in performance to TSO'd units.

If this is true, it might relax the requirements for those with Trig TT22 transponders so that they can use cheaper GPS sources like the GRT GPS-EXT-RAIM unit that they sell for just under $500.

I've decided that it's cheap enough to give a try, so I just ordered one and will be playing with it over the next few months. It certainly beats forking out $3000 on the TSO'd unit sold by Trig.

If anyone has opinions, experience or also intends playing with this I'd love to hear. I fly out of Harris hill which is right by a big iron airfield and it'd be nice to see them on a screen before bumping into them. I also like the idea of a couple of us flying with ads-b out so that people around us get to see the in portion. S emus like even a relatively small percentage of us on the new standard could help safety given the idiot decision by the FAA to restrict access to the "in" data to a hockey puck around each plane with "out".

Andrew, although many people want ADS-B to be used for collision avoidance, it's important to understand that ADS-B's original purpose was to improve the quality of the surveillance data that ATC receives. If you stick with that mindset, the complications that followed are much easier to understand..

(BTW - The following are very informative about ADS-B:http://adsbuniversity..com/ads-b-university)

For example:

Problem: Detecting an aircraft's location through the use of radar provides a certain level of accuracy, adding transponder data helps, but what would be best is for the aircraft to report its onboard GPS position to ATC. Solution: Create ADS-B, define the requirements for ADS-B OUT, and require certification so you are sure you know how it works.

Problem: If you are going to use ADS-B information for air traffic control, you want to have some assurance that the GPS data being reported is accurate. Solution: Define the accuracy of the GPS receiver that is necessary and certify it.

Problem: In some places there is a lot of traffic and the transponder based (1090) ADS-B systems might over-crowd the frequency either today or in the future. Solution: Pick another frequency (UAT) that has plenty of capacity and define ADS-B for it.

Problem: The rest of the world isn't concerned about frequency congestion and airlines are less than enthusiastic about having to have both mod existing 1090 transponders and ALSO install a UAT ADS-B box onboard. Solution: Keep 1090 for aircraft that fly above 18,000 since they are the ones that will encounter the overseas environment.

Problem: With two frequencies, the 1090 and UAT don't talk to each other. Not really a problem since the ADS-B ground stations can receive both frequencies and ship it over to the controller. But, okay if it's really necessary, a solution is: When the aircraft are in range of a ground station, re-transmit the data on both frequencies. And keep transponders on *all* aircraft so TCAS can function when there's no ground station available.

You've noticed, I'm sure, that none of these problems/solutions have anything to do with collision avoidance, except in controlled airspace where ATC can see the traffic and issue traffic warnings or vectors. Just like they do today. And new FAA procedures depend on getting the more accurate ADS-B out data. This explains why ADS-B out is further along than ADS-B in, which provides services for pilots, not ATC.

All of this stuff about pilot services like traffic awareness or weather is secondary to the purpose of ADS-B - to improve surveillance data for controllers and FAA. And the concern about frequency congestion still exists, so most of the ADS-B out data will be transmitted on the less congested UAT frequency. That may be crap to many people but it does explain the push for UAT ADS-B systems. The lower cost and power consumption are bonuses but not the main reason.

It's not that FAA isn't interested in improving or developing ADS-B (they are) but that isn't their main focus -improving the quality of the surveillance data they receive. With that perspective, you can see that systems like FLARM, which are intended to help pilots avoid each other without the need for a controller are fundamentally different than what ADS-B was originally designed for. Maybe someday ADS-B will do this, but not today and not in the near future.

Hope that helps sort it out a bit. You have to view it from the main beneficiary's perspective to make the present situation understandable.

On Tuesday, April 7, 2015 at 9:43:26 AM UTC-7, wrote:

Problem: The rest of the world isn't concerned about frequency congestion and airlines are less than enthusiastic about having to have both mod existing 1090 transponders and ALSO install a UAT ADS-B box onboard. Solution: Keep 1090 for aircraft that fly above 18,000 since they are the ones that will encounter the overseas environment.

Isn't it true that most of the RF congestion comes from the bandwidth-intensive interaction of TCAS with Mode C (and earlier) transponders? I've been told that the reason Europe didn't have to go down the UAT (or equivalent) path was because they mandated Mode S. It's possible the US could have done the same, but apparently the FAA didn't want to force a transponder upgrade (which seems silly given all the other mandated equipment and duplicate antennae). And so we get the mess we have that, as you pointed out, the FAA isn't so concerned about because our concerns have little to do with the problems they were solving for.

I remain somewhat skeptical that GA will go en masse to UAT. If Trig comes out with a Mode S/1090ES Out single box that hooks up to an existing Mode C antenna I think it could be quite popular.

Andy