Mode "S" - Rfq [Archive]

rustle

24th Nov 2002, 21:26

QDM,

GA is most definitely affected.

Original timings would have been (simplistically) IFR-ops require mode S by 2003, all other aircraft (incl. balloons/gliders/airships) by 2005.

CAA went for extension. IFR-ops by 2005, all others by 2008.

But, and this is worth remembering, AFAIK the other countries adopting Mode S have not yet agreed a deferral :(

There are currently ZERO Enhanced Mode S boxes available for GA.

Likely outcome from that is IFR-ops will have to seek exemption until the kit is available, on the basis that as soon as kit available, it will be fitted (including proving fitting "appointments" and proof-of-"purchase")

Estimated cost for an enhanced Mode S box: unknown - captive market, high R&D = give them a blank cheque :(

Quite important, really...
---------------------------------
There are currently three very significant things happening in UK that will have an affect on our hobby.

AIS changes
Rule 5
Mode S

Maybe I need to talk Mike into making our website permanent ;)

QDMQDMQDM

24th Nov 2002, 22:36

Does this seriously mean that if I were to go for a potter around the totally uncontrolled, empty airspace of North Devon, as I did this afternoon, that I would have to have a functioning Mode S transponder? What an incredible load of bollocks if that is so. What about non-radio aircraft, gliders and the like? This is ridiculous.

QDM

chrisN

25th Nov 2002, 00:23

QDM, you would have to have Mode S, I would in my glider, and so would everyone else from 2008.

It is possible that this would cause so much clutter on ATC screens that it would then be mandatory to switch it off in some areas, like in Holland beneath their TMA. A recent thread on PPrune ATC issues had several ATCO's saying that they could not cope with all GA including gliders etc. squawking.

(On good days, there are more gliders than anything else flying. During one day, it was found that about 350 transits of Didcot power station were made by gliders.)

The thread on the ATC forum I had in mind was called gliders and transponders, and included the following extracts:
-----------------------
posted 7th October 2002 13:39

In the netherlands gliders are obliged to squawk mode a/c everytime they are flying above 1200 ft. This rule comes into effect by 1-1-2003.
The reason, be-sides european regulations, is to enhance safety and avoid mid-air collisions.
The ironical thing is it is MOST STRICTLY FORBIDDEN to squawk below the schiphol tma........?
[snip]
----------------------------------------
posted 7th October 2002 14:53

I am both a controller and a glider pilot from Germany. I don´t like the idea of every glider having to squawk generally at all...from either side. First, there are not many certified transponders available suitable for gliders (they use a lot of electrical power). But most important is the fact that on a nice weekend there ARE already so many targets shown on my screen, that I can hardly see my IFR-traffic. If every glider would have to squawk when flying in controlled airspace I would go mad because I would see even less. [snip]
---------------------------------------
posted 8th October 2002 09:33

Completely bonkers idea!

Quite apart from the fact that the SSR clutter on radar would drive us to distraction, the lateral and height envelope of a manouvering glider is so unpredictable it would be of little use to us in atc or a TCAS equipped aircraft.

I don't know about the rest of Europe, but in my experience the UK glider fraternity generally operate to very high standards, keeping us informed well in advance of their intentions/operations, and also generally manage to stay away from similarly busy airports/airfields.

----------------------------

rustle

25th Nov 2002, 07:44

Chris,

Just to clarify one aspect, the pilot would not, infact, switch off the transponder - ATC will filter it out and not display your data to avoid "clutter".

You will still be "squawking" (pardon the expression) so that TCAS still functions (notwithstanding the limitations you mention above)

So, buy the kit so you show up on radar, then we'll filter you out so that you don't again...

Who has control?

25th Nov 2002, 09:19

OK, so lets see if I've got this straight.

We need to have Mode S transponders - with height readout, (I thought that was Mode C), so that TCAS will function properly.

At the moment, if I'm down at 1500' with my transponder on and a 747 goes overhead at 25000' its TCAS will flag me as a potential target as it doesn't know that I'm 23500 feet below. Correct??

So this system is of absolutely no use to me at all and is only for the benefit of IFR traffic.

So how about getting Mr Boeing or Mr Airbus to pay for it?

rustle

25th Nov 2002, 10:44

Some of the "rationale" (is that the correct word?) behind Mode S can be found here:

http://www.ais.org.uk/aes/pubs/aip/pdf/aic/4Y065.PDF

Of course, because this is secret you will have to log in to read it :rolleyes:

chrisN

25th Nov 2002, 10:54

Rustle, my comment about maybe having to stop squawking in some areas was based on what happens now (allegedly) in Holland, as I quoted above:

"The ironical thing is it is MOST STRICTLY FORBIDDEN to squawk below the schiphol tma........? "

WHC, TCAS works with Mode C. I have read elsewhere that the TCAS unit in an airliner (say) scans 30 degrees above and below. If true, it won't "see" you when you are 23500 feet below except when you are too far away to cause an "advisory" (instruction to the airliner to take avoiding action).

We could do with some expert posting up just what Mode S brings extra to the party. My understanding is that it would carry info additional to position (Mode A) and height (Mode C) such as registration, make and operator of airliner, whether they need extra baggage handlers or have had a medical emergency and need a midwife or a doctor, etc. - none relevant to TCAS.

For gliders I suspect it would just transmit that "this is a glider", and possibly the serial number of the transponder and the fact that the glider does not itself have TCAS so won't be telling the glider pilot anything to resolve a potential conflict, leaving it all to the airliner (or whatever) to do that.

NigD2

25th Nov 2002, 12:00

Elementary mode 'S' is due to become live in certain parts of Europe from March 2003 but not the UK who is going straight to enhanced mode S in 2005.

A mode S transponder can be configured to transmit aircraft information including the maximum ceiling, maximum climb performance , aircraft type, flap position etc. This is then interfaced to the TCAS, which in the event of both aircraft having TCAS will determine which aircraft climbs and which descends.

Mode C considered to be a poor mans TCAS as the TCAS equipped aircraft will always get the avoidance manourve.

There has been reports in CHIRP of helicopters flying in the London airports area (Heathrow low level corridor I think) that have just been operating Mode A and as there was no altitude transmission, the TCAS has been giving Traffic alerts while on final.

To me as an engineer, the more info that aircraft can pass between each others avionic boxes the safer things will be, then again I'm biased and trying to keep in employment!!!!

Back in the real (to me) GA world, the cost would be extortionate.

FlyingForFun

25th Nov 2002, 12:21

NigD2, if a mode-C equipped aircraft gets too close to a TCAS-equipped aircraft, the TCAS will not give either party any avoidance instructions.

It will tell the pilot of the TCAS-equipped aircraft that you're there. But, unless both parties have Mode S, neither will receive any instructions. Unless you have Mode S, the other aircraft doesn't know what you're doing, so it's not able to give avoidance advice.

FFF
----------

gasax

25th Nov 2002, 12:23

But it gets funnier and funnier - so long as you don't have to actually pay for these things.

The CAA have just issued 'consultation' requiring all Public Transport Category aircraft - regardless of use - to carry Mode C transponders. The legislative impact assessment is pretty short and strangely seems to have ignored the fact that these nice new boxes, costing over £2.5k by the time they are fitted will have to be thrown away within 4 years!!!

Am I missing something or is the CAA trying to clear UK airspace of those bothersome little things to give free rein for Public Transport aircraft over 5700 kg?

NigD2

25th Nov 2002, 12:24

FFF

Sorry, my mistake, finger troubel !!!!:)

Meant to say Mode 'S' alone is poor mans TCAS.

NigD2

englishal

25th Nov 2002, 12:28

A good idea...in theory....if the boxes were provided by the EU. Yet again, the UK / European GA user is going to get shafted.

Maybe they ["Eurogovernement"] could spend less time discussing the number of ° in a banana's bend to allow it to be called a bananna and UK chocolate vs Beligum chocolate, and use some of the cost savings to send every aircraft owner in Europe a Mode-S box.

Why not make it like when cars had to have catalytic converters fitted? Old cars were excempt, but new cars after a certain date had to have them fitted.

Rgds
EA
:(

rustle

25th Nov 2002, 12:50

chrisN

"Rustle, my comment about maybe having to stop squawking in some areas was based on what happens now (allegedly) in Holland, as I quoted above"

I know, but Mode S kit cannot be switched off - sorry I didn't explain that very well :)

Now a cynic might suggest that one of the drivers here is to enable a mechanism for charging (via Eurocontrol/NATS) for flights in "designated" airspace (read anywhere)

Before you laugh, we have a precedent:

Night flight in Class 'G' in a > 2 tonne aircraft when all the LARS have gone home :(

Fuji Abound

25th Nov 2002, 15:55

Joe operates from her privately owned strip in the South of England and his friend is based at L2K. They regularly fly cross channel to meet up. Both have just spent 4,000 euros on a mode S box because someone in Brussels said they must. They didn’t realise it cost another 1,500 euros to have it fitted. Joe found nobody wanted her three year old mode C transponder which was perfectly serviceable, and Pierre had to reorganise his panel because he had not had a transponder fitted before, which cost him another 500 euros.

Joe set off in reasonable visibility, but by the time she got to Dungeness visibility had deteriorated. She had an IMC but knew at the FIR boundary her vanilla PPL would be her only license privileges. She thought she would try Manston for a LARS, but was beneath and beyond their cover. London info had her details, but also could not provide a radar service – they were sorry. Pierre was a bit more fortunate because Lille gave him a radar information service – he was pleased he had the box for 10 minutes until he got to the FIR boundary.

Both were now with London info and both were “surrounded” by the L2K day trippers. London info was manfully coping with all the different position reports, and generally pilots were altering altitude to avoid conflict. Unfortunately both Pierre and Joe altered for another aircraft and ended up on reciprocal headings at the same level. Fortunately they missed, but only just.

Joe and Pierre each fly around 100 hours a year. Joe operates occasionally within CAS, but spends most of her time in Northern France or Southern England were it is easy to avoid CAS. Pierre’s bi-plain is a beautiful old girl – his new mode s box is the only new bit of kit he has fitted in the last twenty years. Other than his cross channel sorties he potters around northern France. Most of the time he is lucky to get a flight information service never mind a RAS, but they told him he must fit the box.

They both wonder whether their shiny new box was worth the price.

bluskis

25th Nov 2002, 16:34

Seeking to make an intelligent comment to the CAA, I posted a question on the ATC forum asking for their input as to how they may be adversely affected if GA (light) were given an exemption or partial exemption from the Mode S regulations.

After all it would be difficult to protest if there were significant safety issues.

So far zero responses.

From what has since been posted on this forum am I right in concluding that there are no significant safety issues?

slim_slag

25th Nov 2002, 20:13

Just a quick read, the 'consultative document' suggests four options. Option 1 is do nothing, all the way to Option 4 which isOption 4. Await the maturity of alternative technologies to Mode S SSR, such as ‘Automatic Dependent Surveillance – Broadcast (ADS-B)’, and implement them at a later date.Funny, but to my reading of the doc the decision has already been made (Option 3), so I wonder what is 'consultative' about it. Maybe I am being cynical.

I think in order to get cheap kit, you need a massive market. I hate to harp on about it, but that means waiting for the US to decide what to do, and then you will get a massive economy of scale. Although Mode S groundstations are alive and kicking all over the US, I get the impression the US has decided to pass by Mode S for GA and is getting into true 'consultation' with the GA community with regard to ADS-B, Option four in the CAA doc.Since ADS-B is a "cooperative" surveillance technique and 96% of the civil aircraft operating in the national airspace system are "general aviation" aircraft, the affordability of ADS-B is crucial to its success. (And don't get too excited, that's the FAA talking)

So it would be a real bummer if you had to purchase and install Mode S kit, then the world moves to ADS-B, and you had to go out and buy some more new kit!

alphaalpha

25th Nov 2002, 20:27

bluskis:

Mode S has been debated on the ATC forum several times. This may be why you are having a slow response.

Last thread I read seemed to conclude that there was little benefit for ATC in having GA outside controlled airspace squawking mode S. If all flying machines so squawked, the radar screens would be so overloaded that they would have to filter-out the squawks of no interest. I believe the TMA controllers (and some airways) filter out 7000 squawks now.

Why not do a search and you will see what I mean?

bluskis

25th Nov 2002, 22:54

Thanks for the info AA

englishal

26th Nov 2002, 07:04

I notice the document is titled:-

"Consultation for The Proposal to Amend The Air Navigation Order 2000 to Require the Carriage and Operation of Mode Select Secondary Surveillance Radar Equipment for Aircraft Flying in Designated UK Mode Select Airspace"

The big question, is what is "Designated UK Mode Select Airspace"? If it is present Class A airspace, then VFR pilots won't have anything to worry about, or if it is like the USA Mode C Veils which only exist 30 nm radius around major airports.....I don't know.....

I have been checking the price of Txpdrs, and the current price is around $5,000 US for a Garmin. Hopefully by 2005 - 2008 the price will drop significantly....though as with everything to do with aviation, the price will remain horribly over priced.

EA;)

rustle

26th Nov 2002, 10:44

EA,

"...current price is around $5,000 US for a Garmin..."

Sorry, a Garmin what? As the requirement isn't yet clarified how can Garmin (or anyone else) quote a price?

Or was that an "un-enhanced-Mode-S" piece of kit?

TIA

englishal

26th Nov 2002, 12:20

Not advertising here but just a few examples:-

"Garmin has introduced a value-priced Mode-S transponder, the GTX 330. At $4,995, the GTX 330, Garmin believes, will be a cost-effective option."

"Bendix King KT70: Similar to KT-71 but DOES include Mode S (Select) capability "

GTX 330 Panel mount, Mode S datalink transponder (black face) $4995

GTX 330 Panel mount, Mode S datalink transponder (gray face) $5237

GTX 330D Panel mount, Mode S datalink transponder with diversity (black face) $9995

GTX 330D Panel mount, Mode S datalink transponder with diversity (gray face) $10487

KT-70 Solid State Digital Panel Mounted Mode S Transponder OHC
*includes installation kit upon request $2750 $995

KT-70 Solid State Digital Panel Mounted Mode S Transponder NEW $5504 $---

KT-70+ Silver Crown Plus Solid State Mode S Transponder NEW $5504 $---

[Not sure what enhanced is....:)]

EA;)

Keef

26th Nov 2002, 17:00

It's all very scary.

Enhanced mode S means, I think, that the transponder tells ATC what you've set on your autopilot, your mag track, number of Pax, number of hot meals left on board, hostie's telephone number, and so on.

That means a "glass cockpit" to feed the Mode S. That's going to look very odd on Tiger Moths and the like, isn't it.

I can understand that if I want to fly IFR in Class A airspace in 2010, I'm likely to need enhanced Mode S. I don't like it, but I can understand it.

For everything else, and up to (say) 10,000 feet, surely common sense should prevail. I would like to see our CAA telling Eurowhatever not to be so silly, and to change the rules they've just dreamed up without use of brain.

An "exemption" is NOT a good idea. Those have a habit of being withdrawn, and anyway don't work elsewhere.

Where is AOPA? Not heard a lot from that quarter about what's being done... Should we all write in to say our views, or will that drown the CAA in conflicting arguments, leaving the "do nothing" option as the best one?

FlyingForFun

26th Nov 2002, 17:17

Enhanced mode S means, I think, that the transponder tells ATC..... hostie's telephone numberCool - how can I get a job in ATC? ;)

FFF
---------------

slim_slag

26th Nov 2002, 17:24

englishal

I haven't reread the doc, but I think you will find that VFR flight in the middle of nowhere gets dragged in around 2007/2008.

keef

:D

I think the only relevant thing for GA traffic with "enhanced" mode S is because it "squitts" your position in 3 dimensions. I get the impression the only thing "bog-standard" mode S does in the GA world is provide a unique key which can be used to look up your tail number and send you a letter for busting restricted airspace. I'm not sure how the EU is going to find out where you are in 3D without using that nasty US GPS system which is totally unsuitable for EU aviation purposes (like approaches) :) Mode S is obviously not required for GA because there is model out there where mode S is obligatory for TCAS (even for on demand part 135 charter operations), and huge numbers of VFR planes not using it is irrelevant.

My airline pilot friends tell me that in the low level airspace where you find swarms of VFR traffic, squawking mode C is perfectly adequate for their situational awareness purposes. They also tell me they would rather you squawk mode C than turn your transponder off and not be able to see where you are. They can filter out all the VFR traffic in busy terminal areas, just like ATC can.

With some digging, there is some good stuff to be found on the FAA web site, and the CAA doc has a bilbliography. Years down the line this technology could be very useful for GA because the mode S (or more likely ADS-B) groundstations will be able to transmit positions of conflicting traffic to you in real time. I think this has been demonstrated in the US, but they are still working out (ie consulting :)) how this will affect the WHOLE aviation sector.

All this is all from a very basic understanding, others will know more.

Cheers

rustle

6th Jan 2003, 17:28

I know you're all busy thinking about my NOTAMs question - so just a gentle reminder about this. :D

Responses need to be received in relation to this by 24 January 2003 (this month)

bluskis

6th Jan 2003, 17:58

I asked some questions on the ATC forum when you posted the first alert on Mode S, and got the impression that there were sufficient problems and sufficient unknowns that the experts would be unlikely to impose mode S on GA without more thought.

If my impressions are wrong perhaps I should panic at the cost implications.

However, the knowledgeable people on the ATC forum threw up so much technical detail that I found it difficult to formulate what might be considered to be a balanced objection.

To object on the basis of cost would be valid, to object on the basis that the cost is not justified is more difficult without really understanding the problems it would cause if GA was exempted.

To object on the basis that there should be cheaper technical solutions to the problems is voicing a suspicion, but without a solid basis of knowledge.

Can you help with a precis of the pro's and cons?

Keef

7th Jan 2003, 00:43

I wrote to my MP asking him to intervene to stop this silliness until someone has PROVED that GA needs Mode S, and that ATC will really use the information.

I got a load of twaddle back from the Ministry, telling me that Mode S is needed for TCAS (wrong! Mode C works just fine) and that GA was consulted. I've not yet managed to find anyone who thinks he/she was consulted - just a few who were "told" this is the way it's gonna be.

Mode S in its basic form does two things in a GA aircraft (compared with Mode C):

1. It provides more detail to Mode S enabled ATC radars - but there's only one of those so far, and when there are more, the Controllers will have to filter it all out again to avoid cluttering their screens beyond readability.

2. It enables Eurocontrol to know when you're flying so that you can be sent a bill for use of airspace. You think the air is free, and ours? WRONG!
You think VFR flights won't be billed? Want a bet?

You have about two weeks to write in and object. DO IT NOW! There's good information on the AOPA website to craft into a suitable letter.

PhilD

7th Jan 2003, 12:12

What is 'notified TMA or En-route Mode S Airspace' (quote from the exemption policy for this proposal). Can I assume that 'notified' means whatever TMAs the CAA decide to include from time to time?

slim_slag

8th Jan 2003, 03:34

Well keef,

If the ministry think the reason Mode S is required is so TCAS will work, and they are making little planes put it in for that reason, the only logical conclusion is that they are going to force little planes to install TCAS too. Otherwise as is well known, Mode C will work perfectly well.

Thank God logical conclusions mean nowt to government departments, or in this case you can only hope so.

Doesn't the CAA say little planes shouldn't use Mode C in airport environments because it upsets people with TCAS???

FlyingForFun

8th Jan 2003, 10:03

Forgive me if I'm wrong, but no, TCAS doesn't work (completely) with Mode C. The airliners will get a TA (traffic advisory - tells the pilot there's traffic, but won't tell him what to do about it) if the traffic has Mode C, but not an RA (resolution advisory - which tells the pilot to climb or descend, after negotiating with the Mode S transponder in the other aircraft).

I want to make it clear that I do not think this is a valid reason for installing Mode S in all GA aircraft! But we need to get our facts right if we're going to complain.

As for not squawking Mode C, the only time I've ever heard this is when I've been told to squawk Standby when approaching airfields like White Waltham which lie on the edge of busy airspace - and that's to avoid cluttering up the ATC screens, not because of TCAS. But, having spoken to the controllers at Heathrow about this subject, I will now continue to squawk Mode C until I'm off the runway. I have been told not to squawk Mode A because of TCAS - I believe that pilots will be given a TA for any traffic in the same area if the traffic is squawking Mode A and not Mode C, even though the airliner is probably over 30,000 higher than the other traffic.

Apoligies if anything I've said in this thread is wrong... it's been about 6 months since I did the exams, and I've forgotten lots since then! I'm sure someone will put me right if necessary though...

FFF
---------------

Wrong Stuff

8th Jan 2003, 12:17

FFF - perhaps I'm being a bit thick here, but I don't understand what the difference is.

If I get a Mode S transponder, the TCAS of an airliner coming the other way is able to chat to my Mode S transponder and find out what level I'm at, the same as Mode C. I can't see where the negotiation is going to come in, though, because I won't have TCAS. Sure, if both a/c have TCAS one can command a climb and the other a descent, but as I don't have it there's no negotiation to be done - my mode S transponder, if it's being honest, is just gonna shrug its shoulders.

Or am I missing something here?

slim_slag

8th Jan 2003, 14:58

fff

AIP ENR-1.6.2,

1.2 In airspace where the operation of transponders is not mandatory pilots of suitably equipped aircraft should comply with paragraph 2.2 [squawk 7000] except when remaining within an aerodrome traffic pattern below 3000 ft agl.

I think it is being amended, not sure whether it has come into force.

My understanding of TCAS, Mode C and Mode S is the same as Wrong Stuff's. I think we all should be using the term TCAS II in here, but that's just a nit-pick.

bluskis

8th Jan 2003, 16:12

We are now being asked to keep squawking C all the way to the ground.

This is per a recent document which I have read, remembered, but forgotten exactly what the document was.

The present and urgent requirement is to be able to submit a credible objection to GA (light) having to buy expensive mode S equipment.

I have yet to look at the AOPA link mentioned, but it would help if those that know post on this forum a credible arguement.

slim_slag

8th Jan 2003, 16:55

bluskis

AOPA should be giving you the information, then you write to your MP, and as keef suggests you get ignored.

Not sure whether this (http://www.aopa.org/pilot/features/future0002.html) is the link you are talking about, but it might interest some. One para says:"

On the downside, Mode S wasn’t really designed to pass huge amounts of data. Update rates of changing traffic situations may drop to critically slow speeds in areas of dense traffic. Also, Mode S doesn’t have a sufficiently wide bandwidth to permit the exchange of weather graphics, text data (e.g. clearances, weather reports) and display traffic. Mode S, you see, already operates on a very crowded frequency—the one that supports TCAS and ground-based surveillance radars. With all those radar sweeps and TCAS interrogations and replies, it could be difficult to use the frequency to display all traffic.

So it isn't too far fetched that you get to pay thousands to install Mode S in your little planes, all the little planes overload the system, and you get told to turn it off :rolleyes:

rustle

8th Jan 2003, 17:38

Bluskis

The thread in ATC Issues, started by Bookworm:

http://www.pprune.org/forums/showthread.php?s=&threadid=73769

Has a lot of info in it.

I particularly liked this quote (referring to the ground installations):

"Have taken some 'expert' advice on this now.

Mode 'S' will not appear anytime soon in UK. Although its essentially a software upgrade for the ATC radars the main UK radars require to be replaced (not only for mode 'S'). NATS had a 10 year plan to replace them all, but the cost is now £150million and with the HUGE debt NATS has the interest repayments have crippled that size of investment."

Another thing, your (GA) Mode S squawk will be "filtered", so no-one on the ground sees it in busy airspace - a bit like the filtering of 7000 today in some TMAs.

slim_slag

9th Jan 2003, 04:18

To filter something, you have to see and process it first, so you know you can ignore it :)

A and C

9th Jan 2003, 07:46

No one has asked the question "where dose the enhanced data for mode S come from ?"

If you all think that it will cost you a lot to go mode S then that is just the half of it !.

Enhanced mode S requires data inputs for HDG, TK , IAS , OAT , PX alt , the only way to get this is from an air data computor (ADC) these cost about $4000 this requires the HDG info from a slaved compass system that has a HDG bootstrap output and depending on the RMI system you may also need an inverter to boost the HDG syncro systen signal and then the whole thing needs linking to a top of the range GPS ( garmin GNS 430 or the like).

The down side to this is the cost , if you dont have a HSI I could see the bill hitting $15,000.

The up side is that the ADC will come with a fuel flow system and real time air data is at your finger tips , if you have the display space you will get a wind speed and direction arrow just like the airliners !.
In short the system is approaching the capabilitys of an airliner flight managment computor , and is hardly a requirement for a VFR trip across the channel.

FlyingForFun

9th Jan 2003, 09:25

Wrong Stuff wondered:If I get a Mode S transponder, the TCAS of an airliner coming the other way is able to chat to my Mode S transponder and find out what level I'm at, the same as Mode C. I can't see where the negotiation is going to come in, though, because I won't have TCASThat's not the way I understood it - I thought that the TCAS-equipped aircraft would still negotiate with the other Mode-S equipped aircraft, and the pilot would get an RA. The pilot of the other aircraft would obviously not get an RA, not having TCAS. But I'm not certain, so I've started a thead on the Questions forum (http://www.pprune.com/forums/showthread.php?s=&threadid=77568) to try to find out.

FFF
--------------