Improve Light A/C Separation
 

New post regarding separation, I feel the Coventry thread is not the best place to continue this. Thanks. :ok:

PCAS for traffic spotting
 

I know it is by no means 100%, but many times I have been flying along, looking out to the best of my abilities - and also many times, head down looking at maps etc. - when my little portable PCAS unit goes off and warns me of another aircraft.
Just a few weeks ago I was flying along maybe 500-1,000ft below a broken cloud base, and the unit went off - warned me of an aircraft ahead, same level. I had been looking out but just had not seen it. I quickly descended by a few hundred feet and very shortly after saw a twin only a few hundred yards away, pretty much nose-on to me, which passed a few hundred feet overhead. Based on the 'big sky' we probably would not have hit each other, but it would have been close.

The unit itself is pretty small, very light, sits easily on top of the panel, and uses 12V power from the panel (or a battery unit I carry) so is no problem to use in the club aircraft that I rent.

It doesn't necessarily give peace of mind, but at least it helps a lot to spot aircraft that are transponding Mode C (or S) and which are a 'threat'. (Of course not all aircraft have Mode C/S, like perhaps the smaller aircraft in the Coventry accident, but it tends to be most of the faster ones, where you would have less time to avoid.)

It was pretty expensive - over £1,200 - but having used a PCAS unit I would be pretty reluctant to fly without.

"Of course not all aircraft have Mode C/S, like perhaps the smaller aircraft in the Coventry accident, but it tends to be most of the faster ones, where you would have less time to avoid."

Thanks for the info. A Rotax or a IO540 makes little difference landing on your lap.:eek:

So by way of resume, and to solicit peoples views, one aspect of this discussion which I find particularly interesting was developing as follows:

Very few light aircraft have "full" TCAS. Full TCAS, in addition to actively interrogating other aircraft, will provide the pilot with an RA, in other words what action to take if a collision becomes likely. (This is a simplistic explanation for the purpose of this discussion).

To keep down the price GA typically uses two different types of systems. The first (such as Skywatch) also actively interrogates traffic which is then displayed on a PFD (moving map) or stormscope showing the relative position of the traffic, its height, its change in height (relative to you) and the trend in its position relative to you.

PCAS on the other hand relies on piggybacking traffic information from ground based radar returns (in other words it is passive, and would not work in an environment without any other interrogators). In its simplest version it indicates range and altitude relative to you. In its more "advanced" version it also indicates direction, but only to the extent of the four quadrants relative to you.

PCAS has some other limitations. A return may not be received because it relies on a single antenna, whereas Skywatch has two antennas above and below the aircraft and mounted externally. PCAS is not approved and it is unclear how well the technology has been tested.

Skyforce typically offers the following level of accuracy:

Range accuracy 0.05nm (typical)

Bearing accuracy 5d rms (typical), 30d peak error

Altitude accuracy +/- 200 feet

I haven’t looked up the figures for PCAS.

FLAME is also used, particularly by the glider community, but very little within powered aircraft. It has some similarities with ADS-B.

I am familiar with the first two and have used both, but not with FLAME.

This discussion I think is relevant to all these systems.

Skywatch say that the intention of the system is to enable pilots to far more readily visually acquire conflicting traffic. They caution that separation should not be initiated until the traffic has been acquired visually. As far as I recall PCAS don’t say anything in their OM, but I may be mistaken (it is not to hand). I don’t know what FLAME say.

The discussion is should you do nothing until you visually acquire the traffic because of the inherent errors in range and bearing accuracy and because the other pilot might resolve the conflict in the same but opposite way to you. Only in the case of TCAS are expected to carry out an RA even if you have not visually acquired the traffic.

I think it is an interesting discussion as to how this might work in the GA environment giving the differences between TCAS and CAS.

What are the differences in environment.

Well for GA traffic outside CAS the traffic has complete freedom to manoeuver both laterally and vertically as it wishes. In other words as we all know there is no need to tell anyone that you are departing from your heading or altitude. Moreover other traffic often cannot be verified by reference to ground based radar because the traffic is not receiving any ground based service.

So the question is, in short, outside CAS do you make any adjustments to avoid an apparent conflict with other traffic based solely on CAS, or do you always wait until you have acquired the traffic visually however close that may mean you get.

I gave in the previous thread an example. You are enroute, VFR in 4k viz. Traffic at a range of 10k is converging your track at right angles, same height.

Do you:

React immediately either by altering course, height, or course and height,

or

Do you do nothing and wait until you have acquired the traffic visually how ever close that may take you?

Thoughts welcome from anyone using any of these sytems or just interested in how they work in a "non controlled" enviroment with the mix of traffic we are all accustomed to.

Thanks for your post. Now I think we are making progress with a problem that we have to find a solution to.
:ok:

Tcas will only ever be reliable if all aircraft are forced to be transponding. That is the case flying in the IFR invironment of airways.

The downside out of controlled airspace is that Tcas can give a false sense of security and hence in a certain respect make a collision more likely.

So its really an all or nothing game ie make all aircraft use working transponders ie gliders, microlights light aircraft even balloons before they can legally fly.

Most of us who fly in IMC conditions out of controlled airspace are at risk especially as one poster said when making a cloud break blind to VMC and not knowing what aircraft are circling or flying below the clouds.

Maybe we should consider the possibility of a complete network of radar coverage to be allowed to fly in IMC offering RAS or RIS services but even that is not foolproof especially low level.

The only "almost foolproof system is a combination of both ie TCAS and radar from takeoff to touchdown or controlled airspace.

Pace

Pace. Please can you explain how. Transponders alone do not give you separation.

Fuji, you may wish to know it’s “FLARM”, not “Flame”. The Flarm people emphasise in their manuals that it is an aid to lookout and visually acquiring other Flarm carrying aircraft (and/or obstacles in its database – in Switzerland, cable car cables etc.), not a collision avoidance thing in itself.

From their website: “FLARM is designed and built as a non-essential 'situation awareness only' unit to support the pilot, and cannot always provide reliable warnings. In particular, FLARM does not give any guidance on avoiding action. Under no circumstances should a pilot or crewmember adopt different tactics or deviate from the normal principles of safe airmanship.”

My comments are limited to “Original FLARM for gliders and portable use” – I see that they now have other products including one “for GA” – dunno what that does.

It does have algorithms that separate what it deems non-threat (e.g. formation flying, gliders sharing a thermal and on non-intersecting courses) from threats – projected collision paths. So it does not do the same job F-F as Txp-Txp or PCAS-PCAS.

FLARM is the ONLY solution available now and in the foreseeable future that all, or almost all, gliders could use – because its battery requirements are low.

Sorry it’s not interoperable, but that’s a fact. Transponders are also not interoperable – notably, with things that can’t carry enough battery and/or can’t install it, as well as not being interoperable with other transponder-carrying aircraft unless they have TCAS or PCAS or something like it, or ATC and a totally known environment.

I presume other glider pilots who have it believe, like I do, that Flarm is the best available tool for us at present. I leave others to judge whether it could be so for them.

Chris N.
[edited to add points from Flarm website]

chirsN. Many thanks. Your post is exactly how i see the situation to date. You have seem to posses an in depth knowledge of the Flarm system please let us know all you can.

TCAS comes in two flavors; TCAS I, and TCAS II. TCAS II provides resolution advisories, whereas TCAS I does not.

Even a professionally installed TCAS II system in a radar environment has it's limitations. It's a tool, but still misses traffic, and collisions still occur with TCAS onboard and functioning.

See and be seen is still the best policy, with everything else serving only to back that up.

I never said transponders alone would, but if you have TCAS you will not pick up non transponding aircraft.

TCAS is a tool but can give a false sense of security making you believe you have a shield of protection which you do not have.

In the same way an RIS also gives you a false sense of security. How many times do radar miss an aircraft that passes in front of you?

Pace

This is why TCAS is a dead duck as far as light aircraft/ microlights and gliders are concerned.
The cost alone will prevent most people from installing such a system.

R400

If my PCAS is showing a contact closing steady at the same alt I may change my alt to avoid. If above and coming down I'll make a judgement as to what to do depending on the rate in change of height and difference in height. Doing nothing does not make much sence to me.

Robin

It may be a dead duck as far as gliders microlights etc are concerned but transponders fitted to those aircraft will at least allow aircraft fitted with TCAS to see them.

A white glider circling in one spot under a cloud is not very visible especially to a twin prop chopping in and out of cloud, IMC one second VMC another second.

Maybe it should be a choice to have TCAS but compulsory to have at least mode C transponder for all flying machines?

Pace

Pace. Do you have Tcas II or a variation of ?
Robin.
Without doubt that is correct. TCAS II warnings with no level displayed frighten me to death!!!:eek:

I detect the same prejudices in some quarters here as happens with GPS.

TCAS allegedly damages your lookout.

GPS allegedly damages your traditional navigation skills.

Why not just have a long spike in the middle of a steering wheel, and ban the use of seat belts. It would do wonders for road safety - without a shadow of doubt. Mandate crossply tyres, with excellent aquaplaning properties, for good measure.

But seriously, in the GA OCAS context, one uses TCAS to assist in visually spotting the target, and if one cannot visually spot it then one has no option but to take avoiding action based on TCAS alone. It is better than doing nothing.

Just to clarify terminology.. . . .

When we refer to "TCAS" it is only applicable to "TCAS II" equipped flying machines.

Is it possible to fit an error free static source to microlight type aircraft?

If not the mode "C" is of no value.

TCAS cost - well the Avidyne TIS starts at $10,000 and moves on up. Skywatch $19,000 and on up.

FLARM £350.

Wonder which is likely to have any substantive takeup?

Perhaps a little more time looking out of the window rather than playing with the 3285 GPS functions and dreaming of a "magic" bit of kit to relieve us of one more bit of responsibility to avoid hitting another aircraft is the true low cost solution to this problem............... Sorry for the younger pilots that is consulting the large reality display!

“Is it possible to fit an error free static source to microlight type aircraft?

If not the mode "C" is of no value.”

Yes it is. I have an MCR01 home built (the group a version but the micro would be identical in this case). Despite my kit being entirely self installed it works well (BK76a + encoder). The problem with modern 3X micros is not a technical one it is the regulations. UK micros have a max empty weight. The popular designs are built to come very very close to this limit. The CT for example is 1lb under the max. This makes it almost impossible to install such kit. When the CAA was pushing Mode S for all we pointed this out to stunned disbelief. The CAA types initially thought it would be easy to get their own organisation to increase the limit, but this was ruled out completely. This area of flying is the fastest growing and all 2000 ish of them fly around at normal GA levels, at typical GA speeds – VFR day only.

If you add in the LAA aircraft, the gliders etc then there are more aircraft flying at “normal GA levels” without transponders than with. It often amuses me when people complain that pilots do not turn on transponders that they do not have!!

What we need to do to improve separation is to improve lookout. In the gliding world, if you cannot demonstrate a good lookout to your instructor, all the time, you will not be allowed to fly solo. Some people (particularly ex royal observer types) were trained to be very good at lookout. We need to actively teach lookout to PPL’s and test the lookout of existing pilots. This should take priority over any “black box” solution, unless the solution is going to detect non-transponder aircraft.

Rod1

Rod1. Your para 5; agree entirely.

Not GPS but the number of times I've flown abeam the LIC NDB and watched GA traffic pass its overhead at similar levels but seemingly oblivious to each other's presence is quite alarming.

For the record, I do not want any transponder in my aeroplane (I've better things to route the limited juice through and squander lift on); ENDEX. I have windows and perfectly good (and trained, disciplined) MK 1 eyeballs.

Have you told ICAO and all the TCAS I equipped aircraft operators ??

My (limited) experience of TCAS in a 182T (G1000) is that it's useful on route but it's value diminishes as one closes on a GA airport with a busy circuit. Any circuit traffic sends it nuts and the continual TRAFFIC warnings just become a distraction. I guess it's possible we don't have it set up right.

No. TCAS applies to TCAS I, and TCAS II systems, as previously described.

Other systems in use such as TPAS, FLARM, etc, are not TCAS systems.

Rod1 & GBZ...."Not GPS but the number of times I've flown abeam the LIC NDB and watched GA traffic pass its overhead at similar levels but seemingly oblivious to each other's presence is quite alarming"

I'm quite astonished to see the amount of traffic that uses airfields as navigational waypoints by flying directly over them at 2050' (estimated!). Common sense suggests to me that flying directly over NDB's/VOR's/VRP's and airfields is best avoided, particularly at around 2000'. Why don't pilots navigate with some sort of offset from the feature that they're using ? Actually, thinking about it, the more pilots who navigate this way, the safer it is for me as I avoid such hotspots!

Remember, we as a community, or at least certain parts of it, have "successfully" fought off (at least delayed) "compulsory" transponders for GA. You might say the fight was over Mode S v Mode C, but in practical terms the effect is the same... (quick Google shows an A/C Xpdr at £1, S at £1.5K - each + same installation costs).

The problem you "fight" is that you, with a TCAS / PCAS / Skywatch / FLARM or whatever are expecting / relying on someone else to purchase / fit / get approved a device to make yours work. Some of the latter would, maybe quite rightly, ask you to pay for it? *

I do not know the numbers who have Mode C / Mode S / FLARM / whatever, but for collision avoidance purposes, especially given the lack of radar service(s), we are surely a long way from the "critical mass" to significantly reduce the chance of a mid-air?

NoD

PS before it gets personal, we are just fitting Mode S, but for other reasons...

If on a visual approach, the rule is "see and be seen" 100% lookout and no gadgets to help. I appreciate this as a former fast jet and airline pilot; I also used to be a CVT resident before moving to Scotland, Now a pensioner, too!!:\dbee

Laziness?

Navaids and airfields are all in the GPS database under their normal ICAO code so it's easy to string a bunch of them together to make a route, then follow the magenta line.

(VRPs are a different matter. Most GPS databases have a limit to the length of a waypoint and a VRP like "South Woodham Ferrers" has to be abbreviated, which doesn't happen in a consistent way across GPSs and GPS manufacturers, or omitted altogether.)

But even without GPS, navaids are intended as navaids: string them together to form a route, then fly the route with fairly simple nav equipment. And airfields are rather easy to recognize and identify from the air if your nav is purely visual/DR.

But I agree that it concentrates the traffic, particularly in busy areas or areas without much else to base your navigation on, onto a single point in space. Flying offset (in case of a GPS not that hard to do, just make sure the cross track error is constant at 1 nm or so) would make a lot of sense.

That depends on where you fly. If you fly at 1000ft then I agree 100%. If you fly at 3000ft+ then I am sure nearly all are Mode C/S equipped and transponding.

From my 900hrs of flying, with as much under an RIS as I can get, of the "level unknown" i.e. nontransponding contacts that I recall spotting, countless contacts were below me, and none that I ever recall was above me. (Of course the majority I never spotted). The statistical picture here is overwhelming and that is why I sometimes appear a bit cynical on this forum about the correlation between who is flying without a transponder (often a homebuilt/microlight type) and how low they fly, and probably how far (I mean not far) they fly.

Practically everybody who flies seriously, doing real distances and using the available airspace to the full, has a Mode C at least and uses it. But there is a large and vocal group who are against transponders but who probably do little beyond local bimbles, at low levels.

(time to duck under the barrage of examples of adventurers who flew their motorised hang glider all the way to Kathmandu, etc)

Backpacker - I don't think airfields generally make good waypoints. I would challenge you to to a dead reckoning exercise with say 10 waypoints, all of them being grass-only ones. Some are damn hard to spot for a visitor (easy for locals, obviously). And the bigger ones have an ATZ so you have to be at least 2000ft AGL and preferably more due to overhead joins at 2000ft, and you ought to talk to them. I never use airfields as waypoints, in the GPS route. They have minimal visual benefit - unless it's Heathrow ;)

IO540

“That depends on where you fly. If you fly at 1000ft then I agree 100%. If you fly at 3000ft+ then I am sure nearly all are Mode C/S equipped and transponding.

From my 900hrs of flying,”

The trouble is I have more than 900 hours, I actually fly one of these and I KNOW they fly 2-5000 ft on a regular basis!

“and how low they fly, and probably how far”

A typical 912 powered machine will climb at over 1000 fpm (mine is typically around 1700 fpm) and cruse at 100kn+ (mine does 138kn at 75%). Why would such aircraft a) fly low or B) stay at home. I am based on a strip with 18 other aircraft 2 of which have C of A and most fly significant distances and at normal GA levels using normal GA methods. The majority are flown by ex spamcan drivers who have found a “better” way. If you were to argue that weight shift micros were flown low you would have more of a point (about 3000 aircraft not transponder equipped), but now the engines are getting bigger you increasingly see them at 2-3000 ft too.

The LAA hold a series or regional rallys around the country. You will find 200 + aircraft a day visiting from all over the UK, with some from Europe. The picture of a home built / micro which is just capable of getting airborne is completely out of date. A CT Micro (factory built) will do 120kn with 4 hours fuel, nobody flyes such a machine at low level, too many ATZ, MATZ etc. The 12000 paramoters probably do fly low, but add in the gliders and traditional transponder equipped GA is a minority at 3000 ft on a summer’s weekend

I raise the above so that we all understand the problem. The CAA came in all guns blazing for every flying machine to be fitted with mandatory Mode S. Just a few short month ago they accepted it was an impossible dream for a host of reasons. Current technology transponders will never be made mandatory for all airspace users. If we are serious about improving separation we must go back to basics and be prepared to retrain people in better lookout and test to measure the improvement. This is the only game in town right now. If there is a form of airborne radar we can fit which detects non transponding aircraft, costs 2k and 2kg then I will buy one now, but until then go out and get your eyes tested and clean the canopy.

Rod1

I just knew you would be next in here, Rod1 :)

When is your next trip to Kathmandu?

"If you fly at 3000ft+ then I am sure nearly all are Mode C/S equipped and transponding"

As a converse example, on Saturday 23rd August there were (NOTAM'd) gliding competitions at Dunstable, Lasham, Bicester, Pocklington, Husbands Bosworth and Aston Down. These alone will have accounted for around 200 gliders airborne between 12:00-16:00. Cloudbase in the task area (basically most of Southern England) was between 3000-6000'. Therefore I'm pretty sure there'll have been several hundred non-transponder equipped aircraft operating between 1000'-10,000'. Anybody out flying that might day might ponder on how many gliders they saw (and importantly, how many they didn't).

Is there any interest in a fitting a cheaper system such as Fl..m to all types of light aircraft?

About 30 yrs ago students at Cranfield uni experimented with a system that detected aircraft strobe lights. It was basically sphere covered with photelectic cells that detected the flash from the strobe lights.
This info was then displayed on the flight deck.

With the vast development in electronics since the would this be a possibility?

Outside of gliding competitions, there were also plenty of people flying above 3000 feet on other tasks, whether self-selected or club gliding tasks. I flew from Essex to Saltby, Lincolnshire, and back to Ely, much of the time above 3000 feet. I encountered several other gliders at similar heights, nothing to do with the main competitions.

The previous week, when flying between Cambridge and Suffolk in the Lakenheath area, I heard the pilot of a transponder-equipped aircraft near Bury St Edmunds making repeated efforts for his squawk to be seen, and Lakenheath could see nothing of him, on either primary or secondary radar. So please don’t think that having a transponder automatically makes you visible to air traffic control. Like any other machine, they are not 100% reliable.

Regarding wider use of FLARM, my personal opinion is that for the UK, use by gliders will increase slowly from a few per cent to a significant proportion, when the critical mass will be perceived as being large enough to encourage most glider pilots to use it. Unless something better comes along for powered GA, I think it quite possible that the same thing would happen, with the timing a few years later. [Always provided that it is permitted, and not prohibited, by the CAA or other authorities.] I suspect that the middle phase, rapid increase in use once a critical mass is reached, will happen because those without will be shown how many more aircraft they can’t see that are in fact detectable. Just my opinion.

Chris N.

IO and Rod

I think there are a few issues at work.

I commented earlier on a recent trip to the West Country.

In both directions it would have been difficult or impossible to fly at altitude without an instrument rating. This summer such conditions have been a common feature of the weather. To remain "VFR" (and even then not strickly legal) you might have weaved around the cloud or found a route on top but even then without an instrument rating a route down was far from assured.

I think this means that had the viz been 10K with a base well above GA levels there might have been more of a mix of traffic but the fact of the matter is there wasnt and that seems to be typical of any number of trips this year.

For that reason I think LAA types will often be "held down" by the weather but when the weather is good we will increasingly see their numbers grow at higher levels.

In my view there is no doubt the percentage of faster traffic has grown. As you say LAA types are flying at speeds that were never obtainable not that many years ago and there are more fast singles around.

To nail my colours to the mast I dont believe see and avoid works - or should I have said works sufficiently well enough of the time. The faster the traffic the more this becomes true.

It leaves me wondering if we are not going to mandate the carriage of transponders for all traffic we should mandate its carriage for traffic flying above a certain speed or above a certain altitude (regardless of the class of airspace). At least that would mean in the second instance we could be assured that en route above a certain altitude we were no longer totally reliant on see and avoid.

I remember many years ago coming across a hang glider at just over 5,000 feet. Given that the terrain was at most 700 feet I never expected to see him there (all his mates were at least 2,000 feet below). He was legal and he was entitled to be there. Perhaps I should even have expected to come across him. However, despite his slow speed he presented a very poor target - I hasten to add we never the less managed to avoid each other!

I appreciate this may not suite the gliding community or some paraponting and hang gliding sites but how much of this traffic is en route? NOTAMing or establish "danger areas" around sites with non transponding traffic operating above the transponder base might help accomodate all.

Already is is it not? Mode C compulsory > 10,000' I think: I suspect you mean though wanting a much lower altitude e.g. confining the nasty LAA types to <2000' where they can have even more chance of bumping into each other :oh:

NoD

Yes

No

Confining non transponding aircraft of any type.

I wonder what percentage of LAA types are unable to fit a transponder (because of weight or power) and what percentage are unwilling because of cost?

Or just don't want to full stop? Bear in mind the recent campaign by the LAA (and others) to stop mandatory Xpdrs...

I am not sure it would achieve much, since mid-airs seem to happen in the lower levels (?), and you would still have to transit in and out of the "upper areas" through the "danger zone" (unless you could confine that to CAS).

The 10,000' is a long established rule? What would you change it to? On what basis/reasoning? What arguments would alter the debate we have just been through? Would it be amsl? Or agl?

NoD

I started this thread to try and prevent another terrible accident.

It seems to be going the way of most threads and ignoring the core question.

How can we stop banging into each other?


We all have to share the same airspace irrespective of the type of flying we do.

Please lets try to have constructive discussion.

NoD

For the purpose of debate (because I am not certain my proposal is serious)

1. I agree most collisions occur in or around the circuit. However, see and avoid should work well in the circuit (the fact it doesnt may be for other reasons). Nearly all the traffic (around GA airports at any rate) is likely to be slow moving. The circuit should help pilot's know where to look for traffic. Where there is AT they should provide additional help.

2. The 10,000 foot rule is well established but how much GA traffic is there above 10,000 feet? Very little. Oxygen constraints provide little headroom above 10,000 feet for most, combined with semi-circular or quadrangle levels and CAS. In short I would suggest the 10,000 rule is largely irrelevant to GA.

3. Providing a corridor above the terrain but below transponding height would point in favour of agl however I am not in favour of the use of dual or alternate altimeter settings.

4. Perhaps 10,000 feet is simply too high to be relevant but that opens up the debate as to what would be a more sensible height / level.

5. As I commented earlier perhaps speed would provide a better common demoninator. How many aircraft capable of flying above 100 knots indicated are incapable of fitting a transponder for reasons other than cost or desire?

Robin 400

I dont see your point.

I agree there are many aspects to avoiding collisions. Only one aspect is the impact of PCAS, TAS and TCAS but I think it is very relevant. A PCAS unit can now be purchased for a few hundred pounds and fitted to anything that is capable of getting airborne! I have noticed the up take of these units has significantly increased but of course there is no relevant training involved in their use and their limitations.

By all means lets discuss how we can adapt our flying to reduce the risk of collision a very effective means of reducing the risk - the floor is yours on that topic as you wish. I will be happy to chip in.