PCAS collision avoidance
 

I heard yesterday about the tragic collision between two RAF Tutors, killing two instructors and two young air cadets. I recall hearing about one or more midairs last year as well.

A large number of aircraft are now fitted with transponder equipment. Because of the number of ground stations and commercial air traffic, this equipment will be interrogated regularly. PCAS units (passive collision avoidance) would therefore function well if used sensibly by pilots.

Both the Tutors were fitted with thousands of pounds worth of transponding equipment, which was useless to them because they did not have a 300-pound gizmo fitted.

I would like to hazard a guess that in most airproxes between 2+ seat aircraft, at least 1 aircraft has a transponder. Therefore, the collision could be avoided with a simple, comparatively cheap unit which every pilot could carry - it runs on AA batteries.

The accepted position of GA on any cost related issue is to put its fingers in its ears and dig its heels in. Why, this time, don't we be proactive and invest in the technology which could have saved two young lives, and those of their pilots? Even, dare I say it, pressure the CAA in to making it mandatory, so if your aircraft has a transponder, then you know that everyone else will see you?

The problem with the £300 one is that it doesn't tell you the azimuth (heading) of the conflicting traffic.

To get the one which gives you some idea, it is the £1000 one.

But all these are - for paperwork / regulation reasons - portable cigar-lighter-plug type things which IMHO put a lot of people off because you end up with the power lead strung across messily the instrument panel.

If one could fit the £1000 one somewhere neatly, that would be something else, but there is no legal way to do it because it is not certified for a permanent installation (not in a G-reg, for sure).

A proper installed system starts at around £10k, but is rendered much less than useful by the number of planes whose pilots are exercising their free citizen's privileges and flying with transponders turned off.

It brings it home to you how inadequate see and avoid is, when it fails so tragically for two experienced RAF pilots. I'd support any proposal to make mode C mandatory in all powered aircraft with electrical systems. That should encourage the take up of collision avoidance systems, and so reduce their prices.

... but the problem remains PCAS only detects transponding aircraft. You may end up coming into conflict with a Luscombe (see AAIB Feb report) or Jodel without a power source for a Tx and PCAS - both power-hungry.

I tried the £300 one coming out of the PFA Rally some years ago. The sky was black with departing aircraft but not a squeak from the PCAS, which burned through the batteries in very short order.

When aircraft are outside CAS there is no requirement to be on radio or they might even have been talking to different operators. The Luscombe incident makes it clear that even if they had asked for a LARS service, it wasn't available.

Lookout isn't perfect by any manner of means, but often it's all we have.

Does anyone else have experience of how well the units work?

On the point of it not providing bearing info - I would hope that if a unit told you that there was traffic nearby then you would find it visually, regardless of what info it gave - and that range and altitude would be sufficient for this. If it is out of line of sight behind the aircraft, then odds on it won't be a threat in most cases, at it will either see you ahead, or have insufficient speed to catch up.

I have seen euipment on sale for installing in a panel and hooking up to the electrical supply for the 300-pound set.

In the case of the two Tutors yesterday, they would very probably have been in range of a ground station interrogating their transponders, and therefore the equipment would probably have prevented this tragic accident from happening.

Flarm would also have almost certainly helped avoid this, but GA is apparently largely in ignorance of it or resolutely against fitting it, even though many GA pilots continually complain about gliders being a collision hazard, and UK gliders are getting Flarm in increasing numbers.

(Unlike PCAS, Flarm alerts when a collision is likely i.e. converging tracks, not just another unit in the vicinity which may not be a threat; and it shows the direction of the threat. It does not alert nearby but not converging track units.)

Same arguments as PCAS re wires etc., however – it would for most people be a portable piece of equipment, needing a battery supply or lead to a lighter socket or something.

As I have posted several times before, GA power/power collisions are more frequent than GA/CAT (civil air transport - thankfully none yet in the UK) or unrelated power/glider (only about 4 in the last 30 years).

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. 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.

see Flarm - Homepage

(No commercial relationship with Flarm, just a customer).

Chris N.

I do not know what the cause of the RAF Tutors accident was, but there is a possibility they were formation flying so PCAS would have been irrelevant.

If you take the recent AAIB report on the Staffordshire mid air (See separate thread) then you get an interesting picture. The vintage aircraft spotted the Micro, took avoiding action and was collected by a turboprop. The vintage machine and the micro had no transponder and there was no radar service available in the area. If the turboprop had had PCAS it would have failed to see either of the other aircraft, but see and avoid avoided the potential conflict between the vintage machine and the micro.

I fly from the same strip and the vintage machine and about 80% of locally based flying machines are not transponder equipped. It if far more likely that I will fit FLARM than PCAS.

Rod1

soay:I presume like everyone else you don't actually know (a) what these aircraft were doing when they collided, (b) whether they knew of each other's presence, (c) whether the pilots were RAF (not all AEF pilots are) and (d) how experienced they were. So I think drawing conclusions about the efficacy of see and avoid may be a tad premature.
NS

Off topic I know, but on the BBC site but one of the eye witness did mention something along the lines that "she didn't think planes flew that close" and "for a couple of minutes". So in that case PCAS wouldn't help.

Flarm is basically a 576 Euro TCAS box for us little guys.

Two bureaucratic obstacles to Flarm:

• Not Invented Here as far as ICAO is concerned -- TCAS will have to be pried out of their dead fingers:}
• The manufacturer refuses to sell in North America because of product liability issues

Were I ICAO dictator, I'd buy out Flarm, license it worldwide and mandate an appropriate version (extended detection distance) in airliners so that they could spot the little guys in good time.

Sure beats putting Mode S in everything that flies when radars and transponders are on their way to being superceded by ADSB:confused:

As to whether the Tutors were flying in formation, I would say almost certainly no - formation flying in AEF, due to the presence of civillians on board, is usually an absolute no-no.

PCAS works fine
 

I have had one of the £1,000 units (Zaon) for around 18 months and found it works very well. It gives approx range., approx heading and altitude w/altitude trend, plus an audible alert 'Traffic' in the headset if something is near.
It is a minor pain having to put it in the rental aircraft with wires each time, but there have been enough times it has alerted me to close traffic - which I have not seen before the alert - that I would not want to fly without it.
Of course, you look out as best you can but you are bound to not see some other aircraft.
Obviously it does not pick up everything - only those with transponder on - but I would rather be alerted to at least some of the other aircraft than none of those that my Mk1 eyeball has not spotted.

http://www.aaib.gov.uk/cms_resources...AY%2002-09.pdf

from the AAIB report into the mid air collision in December 2007

"Following the accident to G-AKUI and ZK-KAY, AAIB investigators discussed mid-air collisions involving recreational aircraft, and electronic conspicuity, with staff at the CAA’s Directorate of Airspace Policy. The Directorate staff explained that, although they perceived a widespread concern about mid-air collisions amongst participants in recreational aviation, they were also aware of strong opposition from aircraft owners to mandatory requirements to fit transponders, on the grounds of complexity, cost, and weight. For these reasons, proposals to mandate widespread carriage of Mode S transponders had been withdrawn, and more limited proposals had been put forward for consultation. These proposals did not amount to an effort to reduce the collision risk between recreational aircraft, but only to protect aircraft operating inside controlled airspace from collision with recreational aircraft."

Whilst this is the mentality, there will always be collisions between recreational aircraft.

The human eyeball is simply not enough for collision avoidence

From the above aaib report
 

Please don't take that comment at face value. There are genuine reasons why the recreational fleet has been contesting the Mode S hype from the CAA.

These include cost (up to £5k to fit a Mode S when the aircraft might be worth less than that) and practicality (no power source or battery life less than the length of a day's flying. There is little gain in safety except for the very short period when a commercial aircraft flies in areas where GA is prevalent - Class G. GA gets very little from that.

We were promised by the CAA a low-cost, low-powered Tx but this is years away. Add to that the cost of a PCAS and and that would wreck any idea of low-end aviation.

Don't ever think that we are hostile to appropriate use of technology - in the case of the Luscombe fatality, the pilot died, while the bigger aircraft landed successfully. It is likely to be the smaller aircraft that will come off worse.

But given that the ATSOCAS services are variable, carrying expensive kit will not give much in the way of safety. Look at the proposal for Jersey Zone, for example. In future when you ask for a Traffic Service it will be downgraded to a Basic Service - ie non-radar derived information.

I missed that. How can that be? All traffic in the Jersey Zone is special VFR, which means positive control (and seperation) by ATC. How could you get a traffice or basis service while ATC provides seperation?

Is the proposal to downgrade the class A?

I totally missed whatever it is you're refering to. A link would be much appreciated ;)

dp

From BBC News:

Flying Officer Hylton Price was a retired wing commander who was part of the RAF voluntary reserves and an experienced instructor. He was a former Tornado and Phantom jet pilot.

Flt Lt Andy Marsh, who had "excellent flying skills", was only promoted last week and was waiting to start advanced fast jet training at Raf Valley.

Gp Capt Andy Naismith said that there were "very strict rules" to ensure planes did not fly too close together.

Seems likely that they were better pilots than most of us, but still did not see each other.

This would not surprise anyone who's flown with TCAS, or a radar information service, because of the number of times you're warned of aircraft that you can't see - even though you've been informed where to look.

I agree, TCAS makes you more concerned about maintaining a good lookout because you realise how many you probably failed to see before you had use of it. Conversely, pilots not having had use of TCAS or similar systems probably have a false idea of how busy the sky actually is. Even in 8/8 blue conditions the human eye is not good at spotting fast moving targets which occupy the same part of the retina - i.e. are on a collision course.

I am surprised given past discussion on this issue some of the misconception here.

Zaon Pcas units are the ones we talk about. There are two versions. The difference is the more expensive one indicates the compass quarter in which to look.

Having used both units alongside Skyforce CAS I can report that their accuracy is outstanding.

Both units give a range and altitude difference. This means it is relatively easy to determine if traffic is getting closer and is at the same height. There maybe sound theoretical grounds for not reacting to traffic you cant see, however if the traffic is getting closer and is the same height adjusting to ensure vertical seperation has in my experience always avoided a conflict whether or not I could see the traffic.

It is interesting to note on how many occasions you never see the traffic or when you do just how close it is. Knowing the quarter in which to look to spot the traffic is a benefit but I am not convinced the benefit is as significant as you might believe.

The cheaper PCAS unit is self contained. It runs on two AA batteries for at least four hours. There are no trailing wires. It is easy to stick to almost anything. The more expensive unit does require an external power source but it is easy to connect a small battery pack.

All these systems rely on the other aircraft transponding. I am constantly surprised by how many are, particularly the higher you are and the worse the weather. You are inevitably most at risk low level on a sunny day!

In my view these systems significantly reduce the risk of a mid air. They are not a substiute for maintaining a good look out nor do they detract in any way from doing so.

Until flarm stop having anticompetitive, locking-in, unethical business practices they can sell their stuff to themselves.

They have at least on death, a friend of mine, on their shoulders. Don't ask me for details, but if they weren't such a bunch of bastards, there is a chance he would be still alive.

...

http://www.pplir.org/images/stories/...seyatsocas.pdf

I used to use Zaon PCAS (the cheap and highly transportable one). It is good, but not the be and end all. If you rent aircraft then you may have issues with false alerts. The reason is that the unit makes assumptions about attenuation of the signal to determine range and sometimes thinks the host aircraft's transponder is a threat. Once you have figured out the best placement then it should be OK or else the host transponder is weak and needs a seeing to.

No issues in my cub though, no tranny :) I have to say by and large it didn't detect that many other aircraft that I wasn't aware of from R/T, in the time (albeit just a few months) I flew with it there weren't any significant threats. It was certainly reassuring when in IMC to get traffic information and then see it on the PCAS.

One of the major arguments against PCAS is that there is no way that all aircraft can be fitted with transponders, or that the unit will function reliably. I started this thread about PCAS, but how about now looking at the possibilities of FLARM? It is a low-power unit, which is quite cheap, and could certainly be installed in all aircraft - and provide a reliable traffic warning all the time. How about trying to get this made mandatory? If GA took the initiative on this one (it is, after all, mainly of benefit to us) then it would be ages before the next attempt by anyone to get us to fit expensive and useless equipment. FLARM may also be able to provide warnings in airliners. I certainly dont think we should base our opinion on the post from 'vihai', unless he gives us more reasons.

Surely FLARM is what we've been looking for?

I use a Zaon XRX and swear by it but it does have it's limitations

Firstly of course it relys on other aircraft having their transponder on and it amazing how many GA aircraft you see in TM zones that don't and i'm not talking specials but cessna 172's etc

secondly it does pick up yourself when you alter course and sees you as a threat, that can get a little annoying but easily dismissed as it appears very close out of the blue......

......which means it is of limited use in the circuit. you just get too many warnings and convince yourself you have another or multiple aircraft within feet. It actually freaks me out.

It is fantastic though approaching an airport and transit lanes, high use areas.

As I said in my previous post I am very keen on FLARM. It is far lower cost than a transponder and PCAS, it is portable, battery powered and light. Almost all flying machines could carry it today. It has limitations in terms of range, but it is proven to work in our environment. There are many other potential solutions, but right now this one appears to be the only likely one if we want high take up.

Rod1

Vihai of Milano, Italy,

If you grieve for a friend, I am sorry; as you request that we don’t ask you for details, I won’t, but you can’t expect me to take any notice of your objection to Flarm either, when I don’t understand how intellectual property rights can cause a death.

I’m with Rod on this.

Chris N.

Thanks Robin.

So it's only outside the Jersey Zone that is being effected. The zone stays class A, and SVF and full control & seperation service.

Outside, they will only offer a basic service. From memory, they always dumped me once outside the Zone anyway, so I never got a RIS from them.

dp

So what we've basically concluded is that PCAS is useful, but has limitations (lack of transponders in many aircraft, unreliability), but FLARM seems to work (in a limited range), the only obstacle being that the idea may never catch on to the extent that there is a point in having one installed.

So a rather contravertial idea - how about petitioning the CAA to make FLARM (or a similar system) mandatory? Midairs would become a thing of the past, and it would greatly improve the image of GA in many eyes. At 500 pounds a shot (or much less when demand picks up) this would seem to be a very real solution to this massive problem.

Who's with me?

The problem with any system is that it can get you into trouble. In the case of the Staffs incident see and avoid worked, the vintage machine turned to miss the micro and that put it into the path of the turboprop. I think this could happen with any system. If you also consider formation mid airs and Gliders you will never get to zero. The FLARM system could offer valuable assistance, but why not try to get the various bodies to recommend it initially?

Rod1

I use a Zaon XRX linked to a Garmin 496. Works well enough for my needs which is to give me alerts while I get from a private strip into the airways.

As I understand the matter there is no generic FLARM. A regulatory authority should not approve FLARM for this reason alone.

It also cannot make sense to have two incompatible systems in use. Transponders are already so well established there is no possibility of FLARM becoming a widespread alternative.

I feel sure that eventually ADS-B or son of will eventually replace both.

Only up to a point. Our dear friends at the CAA would only permit ADS-B when linked to a fully approved GPS - not a Skymap III/Garmin 196 etc. So although it might well be a good thing, the devil (and massive cost) is in the detail.

ads-b
 

Information from my sbs-1 shows how many modern aircraft do not transmit ads-b data. It seems strange that although equipped with mode s transponders, they are not fully configured.

“Transponders are already so well established there is no possibility of FLARM becoming a widespread alternative.”

Do you think so? In aircraft which typically fly around below 5000ft VFR? I would have thought Transponders the exception. The Micros, LAA, Gliders etc have much bigger numbers and are mostly not Transponder equipped. The CAA tried to force Transponders on them and failed, this is a much better alternative, and you could of course have both in your IFR wonder ship…

Rod1

Quote:

---

Information from my sbs-1 shows how many modern aircraft do not transmit ads-b data. It seems strange that although equipped with mode s transponders, they are not fully configured.

---

To feed 1090ES ADS-B info into a extended squitter capable Mode S transponder (most are capable, the Garmin 328 and Funkwerk TRT600 are exceptions) requires the position/vector information to supplied by a IFR certified unit.

The vast majority of GA aircraft don't have appropriate equipment, so won't have ADS-B data.

No way. Transponders are the norm in VFR under 5000', not the exception. You do tend to mythologise sport aircraft (gliders, micros etc) as dominating private aviation and I think this simply isn't true. Whatever the number of aircraft is by category, the sporty ones must simply fly less. I don't ever recall a flight in which the majority of other movements I encountered were non-transponder. I am sure there are bubbles of airspace around in which this is the case, but no way are transponders an "exception".

I understand the issue with gliders, but I am confused about micros and LAA. You are always extolling the virtues of these aircraft compared to "spamcans" that will be resigned to history's dustbin. Suddenly a "spamcan" able to carry a transponder and supply it with power becomes a "wonder-ship". Which is it? Are Micros and LAA types able to carry sensible loads and useful avionics, or not?

The CAA was wrong to over gold-plate the transponder requirement with mandatory Mode S for everything. FLARM sounds useful for the hot spots of sport aviation, but a certified technology is the only universal solution. Just squawking Mode C is massively useful to all the TCAS, TAS, PCAS fitted aircraft and ATC SSR and should be encouraged for anyone who can fit one.

brgds
421C

So, the bottom line...

Is there a system superior to the FLARM-type system, which A) does not require a power source other than battery, B) costs as little as the FLARM and C) is always effective in alerting to nearby traffic?

If there is, then tell us about it. However, I havn't seen one - transponders and their receiving equipment are costly (particularly the active receiving boxes - 10,000-pounds) and consume a lot of power. ADS-B and ADS-B receivers will probably be similarly expensive and power-hungry. Neither, as far as I can see, could form a system capable of being fitted in all light aircraft at a low enough cost.

There will always be some new 'wonder unit' just around the corner. But some time, we need to take the plunge and settle on one type of unit. I understand that there are a number of companies producing FLARM-compatible equipment, so there is no monopoly problem. Maybe making them mandatory is a bit radical, but strongly encouraging their use by various means, perhaps followed by making them mandatory, would seem to be a good idea. They seem to be proven in the gliding community.

Any thoughts?

Of course there is no such box but you knew that :)

The point here is that technologies exist which are a lot better than the traditionalist-favourite Mk1 eyeball.

If people who can have transponders (the great majority of planes that actually fly for real, and I don't mean the 1-in-a-million Thruster pilot/adventurer who flew all the way to Kahtmandu) put in a straight Mode C unit, we would get

- a meaningful RIS, without the useless "level unknown" majority of reports

- TCAS activation in commercial aircraft, protecting GA's interests against the regulators

- TCAS activation in private aircraft whose owners have chosen to spend the money

- less resistance to CAS transits

- less resistance to CAS expansion (to a large degree because non-mode-C traffic flying under CAS has to be assumed to be OCAS, and thus far the luck in that daft assumption has held up, despite the hundreds of known CAS busts each year...)

As 421C says, it is completely misleading to suggest that non-powered ultralights or whatever make up the majority of GA. They do occassionally bust some piece of airspace as a group of 20+, all flying together, but that isn't quite the same thing :)

Trig TT21 Transponder

Very small, and compact, minimal power with battery power only around the corner. Combine the new generation of mode S units with PCAS and a TAS system is a reality. Price is still a factor and FLARM clearly has more than the edge in this respect, but sadly aviation was never cheap - but you knew that anyway.

FLARM has low power consumption because it transmits at low power and is therefore low range. It costs less than a transponder because it does not meet a certified standard. If you mandate FLARM, and therefore require certification, and increase its power to something more generally useful, you end up with something that is as expensive and power hungry as Mode S.

What we need is a low power, uncertified system that works over 1090ES and is therefore compatible with the vast installed base of Mode S and TCAS.