SSR in the Aerodrome Traffic Pattern

[2 sheds]

Re the latest addition to MATS Pt 1 (UK), does anyone have practical experience of this yet?

Aerodrome Traffic Pattern Conspicuity Code (7010)
The UK SSR Code Assignment Plan includes a conspicuity code 7010, which may be allocated by ATS units, or selected by a pilot as local procedure may require, when the aircraft is operating in or within approximately 2 nm of the aerodrome traffic pattern. The purpose of this conspicuity code is to facilitate greater availability of the collision avoidance function provided by ACAS. It also allows a unit with appropriate surveillance equipment to filter or highlight the aircraft’s position symbol as appropriate. Considerations for the use of 7010, specific to an individual unit shall be documented in MATS Part 2.

ATSIN 100 also refers, with further explanation, including no longer instructing aircraft to squawk standby when entering the ATP.

If the stated intention is to "facilitate greater availability of the collision avoidance function provided by ACAS", how is the end result going to be anything other than unwanted TAs and RAs? Queried with SRG regional inspectors - they don't understand either!

[chevvron]

LTCC are actively discouraging use of 7010 as it doesn't 'fit in' with CAIT, so you probably won't see it anywhere in southern England.

[2 sheds]

Chevvron

Could you amplify, please? At what aerodromes is LTCC "actively discouraging" it, and with what authority? What is the perceived problem?

2 s

[Dizzee Rascal]

LTCC are actively discouraging use of 7010 as it doesn't 'fit in' with CAIT, so you probably won't see it anywhere in southern England.
I'm watching a 7010 going round the circuit on 7010 at the moment, previously the aircraft did not have the transponder switched on at all until instructed to squawk 7010.
Nobody has asked the shift working today not to use it and we are not too far north of the CAS around EGKK and not that far from EGLC either ?:confused:

[chevvron]

Ah but TC Ops only work on weekdays, so you wouldn't expect a reaction until tomorrow.

[TC_LTN]

TC Ops have asked your SATCO if you would not use 7010 in the aerodrome traffic pattern at Biggin Hill and he kindly agreed that you guys wouldn't allocate it. It has been agreed that we will try to get a discrete squawk for the exclusive use at Biggin and I should have some news about this when I indeed drag myself back into the office, tomorrow. I am surprised your SATCO or Bill have not passed it on?

Just to explain the thinking behind our request; At TC we have a number of airspace sharing agreements with various operators/organisations who operate within controlled airspace without making r/t contact with TC, under the terms of an associated Letter of Agreement. Although not specifically written down, we have often understood that these operations would not operate the transponder, if so equipped, to avoid unnecessary clutter etc. With the change in CAA policy with regard to operation of transponders in the aerodrome traffic pattern, NATS policy now requires us to actively encourage every aircraft, if transponder equipped to operate their transponder. We are encouraging the aircraft which are operating under an LoA and not in r/t contact with us to squawk 7010 and will exempt this code from CAIT (Controlled Airspace Infringement Tool) although the code will always be displayed on our approach displays and not filtered. 7000 will always be subject to CAIT activation and will chnge colour and alert whenever the software determines they penetrate controlled airspace.

For the above reasons we are asking units very close to the boundaries of control zones NOT to allocate 7010 but encourage the use of 7000 to enable the maximum effectiveness of CAIT in detecting infringements.

[TC_LTN]

NATS operates just the system you describe by issuing Supplementary Instructions, Temporary Operating Instructions, Operational Notices and Information Notices. We share this information with non-NATS units via e-mail and snail mail but obviously we cannot guarantee that this information gets to the 'troops' at these units in the same way we can with our own Electronic Briefing System. None-the-less, we are always looking at ways of making sure we all have a clear understanding of what is going on even if this means letting the widest community have an insight via PPRuNe.

[2 sheds]

Quite apart from specific considerations with aerodromes immediately below or adjacent to CAS, back to my original query...If the stated intention is to "facilitate greater availability of the collision avoidance function provided by ACAS", how is the end result going to be anything other than unwanted TAs and RAs, particularly with VFR traffic in the circuit very adjacent to IFR traffic, for example, on final?

[throw a dyce]

We have used a local squawk in the circuit for some time now after an Airprox.It seems to work well and has not caused anything like the RA's and TA's that have been mentioned.We also have a great deal of squawking VFR heli traffic in close proximity to ILS traffic again with little problem.
Isn't there something about below 1000ft, RA's and TA's can be expected,but don't always have to be acted on if visual.:confused:

[2 sheds]

That's what I wondered. Would be useful if that had been explained if it is so.

[throw a dyce]

I think RA's might be supressed below 1000ft but I'm really not sure.Maybe someone can confirm or tell me I talking rubbish.We used to get TCAS alerts for every departure at HongKong on 07R.They reckoned it might be off all the aircraft at the terminal,or the terminal itself.If pilots avoided that,they would hit a 3000 ft mountain.Can't win with that one.

[London Mil]

tad, you are correct. RAs inhibited below 1000ft radalt.

[withins]

Working at some of the smaller units, I can imagine the folllowing scenario occurring;-

Phone rings,aero club requesting circuits however a/c has either an unserviceable transponder or is perhaps an older a/c with no transponder at all, not very common these days I know but still a possibility.In the case of the first example it is something I could defineately see happening.

What should the controller then do? I have some initial thoughts, ie accept the traffic give traffic info to other TCAS equipped a/c as we used to but by doing so would be going against the intention of ATSIN 100 and then be open to criticism "in the event of" something happening.

Your views?

[Chilli Monster]

Withins - Transponder is still not a legal requirement in Class 'D', let alone outside CAS. So - in that event, he hasn't got the power to say the aircraft can't fly circuits. "Operate as before" would be the solution. Whether the aircraft is or isn't so equipped doesn't stop the Controller doing his job properly, and if he does that there will be no conflict.

London Mil - not strictly true. There will be no downwards RA's below 1000ft Rad Alt - RA's giving an upwards resolution can still be issued down to 400ft Rad Alt on certain types of aircraft.

And herein lies the problem. How many people here have GA circuits above 1000ft agl? I know 2 Sheds does. There is the possibility that you will get RA's between inbounds on the ILS and aircraft being held on base leg even though you are quite legally using "Reduced separation in the vicinity of the circuit". If that happens then all you can say, as an ATCO, is "c'est la vie" and put up with it - as it's not your problem but that of the persons who have introduced this without fully thinking it through.

[Data Dad]

Chilli,

as TAD has already stated, up here at the Ice Station (appropriate today:ok:) we have been using a nominated circuit squawk for some time now. Add to that the large number of VFR/SVFR arrivals that we integrate into the IFR arrivals pattern and we are talking a very large scale, real world test (they regularly set the SMF going due to [legal] close proximity). I do not know of ONE RA report/go-around that has occurred during that time between these aircraft (movements circa 440 per day).

I think fears are over stated, but the potential benefits are very real.

Finally, in response to the no/bust transponder question - the ATSIN says
The UK SSR Code Assignment Plan includes a conspicuity code 7010, which may be allocated by ATS units, or selected by a pilot as local procedure may require, when the aircraft is operating in or within approximately 2 nm of the aerodrome traffic pattern.Note the "MAY" - it is not mandatory.

DD

[surface wind]

Data Dad,
It may say 'may', but ATSIN 100 also says
In view of the associated reduction in protection from the ACAS ‘safety-net’, such circumstances are to be regarded as exceptional
You can't win :ugh:

[BackPacker]

I don't get it - but I'm just a lowly PPL not an ATCO. If I squawk 7010C instead of 7000C, will that really make a diference to TCAS or other warning systems?

As a low-time PPL (of which you'll find loads of in a regular circuit, or student pilots) I would hate to receive an instruction from ATC (or AFIS or A/G) "squawk 7010" when I'm about to join downwind. A circuit is a busy place, both in the cockpit (reducing speed, getting the flaps out, carb heat on, gear down, you name it) and outside (lots of planes may be around). If I need to bury my head into the cockpit for a good 5-10 seconds to set a different squawk (depending on the exact type of unit, how familiar you are and what the previous code was that was set, it might indeed take 5-10 seconds), is that worth the trade-off?

Let's rephrase that. Every action I need to undertake in the cockpit when joining the circuit, or in the circuit itself, can be done by feel, by ear (RPM reduction) or requires just a very quick glance in the cockpit (check airspeed, three greens, whatever). With proper preparation, I can even set the next radio frequency in standby and it requires me just one button to select that one (ground, for instance). But transponders do not have a standby window, the older ones have four rotating knobs (but I always forget which way they turn), the newer ones have 8 number buttons without any tactile aid. So instead of looking outside for other traffic, I'm now looking inside at a very inconvenient moment.

Don't get me wrong. I'm all for transponders and I even do see the benefits of mode S, despite the costs. But todays transponders are NOT designed so that you can change the code without looking because the assumption is that you will almost never have to change the code in-flight. (Yes, you may need to change it to transit CAS, but there's a reason you need to call 10 miles out or five minutes.) Transponders, precisely because of this, are also typically located at the bottom of the radio stack. (And if there's no room there anymore, somewhere on the right hand side of the panel.) So they're far outside my normal field of vision until I really focus on it. Not something i want to do when joining a busy circuit.

Admittedly, on departure, the problem is less. I can select 7010 on the ground, and a modern transponder has a single "VFR" button which sets 7000 instantaneously.

[BackPacker]

Adrian, I'm not from the UK (although I have a CAA PPL), but why would I not be squawking in the circuit below 3000ft? (Assuming I have a transponder of course, otherwise the whole point would be moot anyway.) Is there a rule against transponder usage when in the circuit in the UK?

And if I were to fly IFR, I would be given a squawk when receiving my clearance, and keep that throughout the flight, not? (Do genuine IFR flights even do circuits?)

[vintage ATCO]

Backpacker

In the UK there was a bit in the AIP about not squawking in the circuit (to reduce clutter presumably) but that has now gone. Where I work we put circuiters on a discrete code to keep track of them on the ATM! Rarely happens now.

In the UK you can fly IFR outside CAS in Class G without a clearance therefore you are not allocated a squawk unless it is a local thing to assist your departure, or you call an en-route unit for LARS. Therefore if not squawking anything else, you should select 7000. 7000 is not a VFR only code despite US transponders being labelled accordingly (OK I know it selects 1200 in the US).

Yes, IFR aeroplanes do occasionally fly circuits.

[BackPacker]

Well, I checked my PPL Air Law and Operational Procedures book (Jeremy Pratt) - they're actually on the shelf directly behind me - and there's no mention of either of these two topics.

No mention of not using a transponder in the circuit. Only this:
"The conspicuity code (7000) should be used when flying in the Open FIR (Class G airspace), unless an ATSU has given you a code to squawk. The general advice is that the transponder is normally set to squawk the conspicuity or allocated code at all times when airborne, unless an ATSU requests otherwise or there are specific local procedures." Nothing in the UK Flight Guide about not using a transponder in the circuit either.

And as my PPL was VFR only and I have no NVFR rating, IFR is only mentioned in passing. But I do know that the UK is a bit different from the rest of Europe, in that they allow a non-IR pilot to file and fly an IFR flight plan, as long as he/she remains in VMC conditions throughout the flight. You guys also have that IMC rating thing where you are in IMC conditions in uncontrolled airspace and separation is only thanks to "big sky, small airplanes". But as far as I know, in the rest of Europe (the world?) you cannot file and fly IFR without an IR, and without being under control of ATC. And they will typically give you a squawk, I guess. Departing IFR from an uncontrolled airfield? I thought that you'd get your clearance, squawk and a void time by telephone? And what about Night VFR in the UK. Does that automatically become an IFR flight as well as far as the rules are concerned?

Anyway, the "VFR" button on the transponder is only a shorthand button for "7000" so if I would be on an IFR flight and felt the need to squawk 7000, for whatever reason, I could use the VFR button anyway... I assume that the same transponders, when sold in the US, would start squawking 1200 when I hit that button. (Perhaps there's even a secret key combination that would allow you to switch between them?)

[BackPacker]

Vintage, thanks. I think we were both typing our replies at the same time, and you were finished earlier. (I had to check my books!)

[2 sheds]

Meanwhile, back at the thread...

The stated intention is to utilise the "safty net" of ACAS, i.e. in effect to deliberately provoke TCAS alerts in the immediate vicinity of the aerodrome. It sounds very much as if somebody is just demonstrating that he is being "proactive" and ticking off some safety "audit" tickbox by doing something! With a mixture of IFR and VFR flights in close proximity, some of the IFRs being separated with "reduced separation in the vicinity..." and the VFRs integrating with appropriate instructions and traffic information from ATC, what is going to be the end result?

What trials were conducted, where and under what conditions - and what constituted a "successful outcome"? I would assume that the only measure of success would be a number of examples of near collisions avoided but no unwanted/unnecessary RAs. Anyone have any info?

2 s

[Data Dad]

2 Sheds - as per my earlier post on page 1..........

as TAD has already stated, up here at the Ice Station (appropriate today:ok:) we have been using a nominated circuit squawk for some time now. Add to that the large number of VFR/SVFR arrivals that we integrate into the IFR arrivals pattern and we are talking a very large scale, real world test (they regularly set the SMF going due to [legal] close proximity). I do not know of ONE RA report/go-around that has occurred during that time between these aircraft (movements circa 440 per day).So whilst not an "official" test, we have been "doing it" hundreds, if not thousands of times and it has NOT provoked TCAS Alerts nor caused unwanted RA's.

DD

[throw a dyce]

Ah but it's Aberdeen so it doesn't count cos nothing happens here.:E:E Actually since we got SSR in 83 we have been operating this system so that hundreds of thousands times.But unless it's been tested ''Doon Sooth'' it means nothing.In fact the Airprox that causes the SSR in the circuit to be adopted here, would not have been so bad had the heli circuiter been squawking.The fixed wing departure would have had a real RA or better traffic awareness.But then helis don't do standard circuits.They even depart backwards sometimes and autorotate from the overhead.

[2 sheds]

Data Dad

Thanks - I appreciate what you are saying, but a couple of points...

Why no TCAS alerts if the aircraft are in close proximity? What would it take in this context to get an alert?

Therefore, what constituted a "successful" trial at those aerodromes where trials were conducted?

[throw a dyce]

They probably get TA's but that adds to traffic awareness.About half of our inbounds can arrive VFR from the east so regular fixed wing operators know that there are numerous helis around.As for RA never seen one,probably because they are supressed.You get the odd request but usually from BA.Also I'll try to tell them about VFR following if I have time.
It's been on trial here since TCAS was invented.

[Data Dad]

TAD

Ah but it's Aberdeen so it doesn't count cos nothing happens here.Oh yes, I had forgotten the "North of Watford Gap" syndrome ! :E:E

2 Sheds,

Why no TCAS alerts if the aircraft are in close proximity? What would it take in this context to get an alert?I make no claims to being an expert on TCAS. Yes, I expect there are Traffic TA "alerts" but that would happen even without circuit traffic squawking (all the other VFR stuff that squawks). From what I know, I believe that TCAS "looks" ahead slightly to determine whether flight paths will actually take the aircraft to the same point at the same time. So, they might be in close proximity (hence SMF triggering) but the equipment detects that they are not going to be at the same point at the same time (coupled with RA inhibition below 1000ft) = no RA's. I am sure a small number will occur - we have all seen the VFR joiner/circuit who insists he has the preceeding in sight but then "carves it up".

DD

[Red Four]

I believe the trial was done last year with 6 participating airfields, one of which was Blackbushe apparently.
CAA were unable to give our unit a synopsis of the trial, and when a request to view their safety assessment (that presumably was carried out on the revised procedure) in order to assist us in our processes, similar response. :ugh:
Can only draw our own conclusions therefore on why this was done.