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alphaalpha
4th Oct 2002, 14:08
At a GA safety evening, I asked the question below, but didn't get a clear answer. Can anybody comment:

In VMC or IMC I can legally fly very close to the edge of CAS, say the Luton or Stansted class D CTA. Controllers provide standard separation to IFR traffic within the CTA. How close to the edge of the CTA will they vector their traffic? If they are applying 3 m separation, does this mean they must keep their traffic at least 3m from the CTA boundary, to allow for possible invisible traffic at unknown altitude just outside CAS?

Does it make any difference if a) the controller has me on radar, ie an unidentified target b) if I am working the controller outside CAS with a squawk and verified mode C?

Is the lowest level you would descend your traffic 500' above the base of CAS? If so, this might only be 600' above me. This is then less than standard separation, isn't it?

This is not just a theoretical question as I often route along the NE boundary of the Stansted CTA in order to avoid the two gliding sites in the vicinity by flying through the small gap betweem them.

almost professional
4th Oct 2002, 15:30
alphaalpha
MATS pt1 states that aircraft inside controlled airspace are deemed separated from unknowns outside, however the controller is told to aim to keep at least two miles within the boundary-to take into account 'unpredictable' manoeuvers.
There may be local differences to this-at our unit we have slight differences in our local orders-but by and large thats how we carry on. Yes you are quite right when you state that if you are under a stub for instance you may be only 600ft below the IFR traffic-this is something that happens a lot under our eastern stub, where the base is 1500ft, but by and large is not a problem-this situation is a fact of life under the london TMA, as my previous existance working at an airfield to the west of stansted showed!
On a personal note I much prefer to be working the traffic thats near the boundary, you may well not get a radar service-but just identifying you can help a lot, again this is not always an option to my busier colleagues down south-please do not be put off calling a unit even if you dont intend to transit the airspace concerned but are flying close to them (no doubt this will set the cat amongst the pigeons with some controllers!)

ATCO Two
4th Oct 2002, 17:28
Hi AA,

In the London City Control Zone we are vectoring traffic at 2000ft downwind for runway 10 only 1 nm inside the boundary of CAS, both North and South of London City Airport. The CTR is only 4 nm either side of the extended centrelines and we are required to provide 3 nm radar separation from traffic established on final. Very often unknown traffic comes right up to the very edge of the CTR in anticipation of a clearance through, before actually contacting Thames Radar. All we can do is pass traffic information to the IFR traffic, there is little room for manoeuvre. If we turn the IFR traffic away we are in danger of losing separation from other IFR traffic in the sequence. As 'almost professional' states, we would much rather be talking to VFR aircraft operating on the environs of controlled airspace as they then become known traffic.

To answer your questions. Does it make any difference if you are known or unknown traffic operating outside CAS in this context? Well accordingly to the book - no. Traffic operating outside CAS is deemed to be separated from traffic operating within CAS, as 'almost professional' has said. Having said that, if I know your intentions and have verified your altitude it makes for a much safer situation.

The lowest level we routinely descend IFR traffic to is indeed 500ft above the base of controlled airspace. The boundary of controlled and uncontrolled airspace must be set somewhere, and to the East of EGLC/EGKB the base is 2500ft, so you can quite legally fly at 2499ft underneath when I am descending to 3000ft. I will sometimes pass traffic information on unknown VFR aircraft to my commercial IFR flights, as they are likely to receive TCAS alerts anyway if the VFR traffic is transponding. The same situation applies to Heathrow Approach descending to 3000ft in the White Waltham area. We cannot practically apply standard separation between known and unknown traffic.

Whilst I am on the subject, the use of GPS has meant that pilots tend to cut corners, and therefore pass very close to the Eastern edge of the London City Control Zone. On Easterly operations and especially on hot days when climb performance is less than optimal, aircraft departing from runway 10 barely make their SID levels by the edge of CAS, mainly due to a very limited track distance from take off. They could come unnecessarily close to unknown traffic just shaving the CTR, and not talking to Thames Radar. Again I would much prefer to have identified the VFR traffic and warned it of the situation.

chrisN
6th Oct 2002, 09:11
The gliders from at least one of the sites alphaalpha mentioned, Ridgewell (where I fly) also go right up to the Stansted CAS boundary - we don't just stay overhead our aerodrome. If we go cross-country West or North West from Ridgewell we skirt the CAS boundary via Haverhill, Linton etc. until we can follow a straighter line to a turn point (usually before returning to Ridgewell - most glider XC's are intended to be closed circuit routes).

On one occasion I was over Haverhill, thermalling, monitoring Essex Radar, and heard them working a power plane round the same edge towards me. They advised him gliders were operating, he replied that he could see none. I called up then, intending to advise my height and position to help avoid conflict, and ATC just gruffly replied "Glider XXX stay outside CAS". End of conversation.

I know ATC can be very busy, but if they can find time to talk to power planes skirting their airspace, they might at least offer the same courtesy to gliders instead of refusing to talk to us at all.

alphaalpha
7th Oct 2002, 08:21
Thanks ATCO Two and Almost Professional. I find it scary that traffic outside CAS is 'deemed' to be separated from traffic inside.

It is inconsistent that you provide 3nm/1000ft separation minima to aircraft inside your known traffic environment, but accept and use 501 feet or 1nm (ATCO Two)/2nm (Almost Professional) minma from unknown traffic (possibly IFR) outside CAS. It is certainly inconsistent, but is it unsafe? To my knowledge, there have been no accidents attributed to such loss of separation. I wonder how often you ATCOs have had to change your plan and vector CAS traffic away from an unknown tracking erratically close to your boundary?

I take your points concerning talking to the ATSU. It works for units like Essex and Luton, but I doubt that the London TMA controllers would welcome calls from GA traffic.

Is there a training point here? Especially in IMC, should pilots routing close to CAS maintain a minimum distance of say 2nm from the boundary? I'm not suggesting a legal requirement, but having heard your comments, it would be good airmanship.

Hooligan Bill
7th Oct 2002, 09:20
alphaalpha,

The real paradox is if the same aircraft is joining CAS under a RAS then the controller must try to achieve at least 5nm radar separation or 3000ft vertical against the unknown. Once it has crossed the boundary and is placed under a Radar Control Service, that requirement technically vanishes.

Duke of Burgundy
7th Oct 2002, 17:15
alphaalpha - interesting debate you started. I take a slightly different view from that of my esteemed ATCO colleagues.

As has been mentioned, the Manual of Air Traffic Services states that aircraft operating inside controlled airspace are deemed to be separated from unknown aircraft flying in adjoining uncontrolled airspace.

If the traffic outside controlled airspace is known to the controller and both aircraft are in receipt of a radar separation service i.e radar control and radar advisory then, in my opinion, the deemed separation becomes invalid and I would ensure that the aircraft were separated by the radar separation standard in use.

I don`t expect anyone to agree with me but that is the way I have always played it.

Bern Oulli
8th Oct 2002, 17:13
Yes there are certainly inconsistencies but Duke of B is absolutely right. If you are working them both under any service that requires separation then that's what you have to do. Separate to the minima required. If the traffic is unknown and outside - ignore it. There is nothing in the MATS 1 that says it has to make sense!

Whipping Boy's SATCO
8th Oct 2002, 17:20
I'm not saying this is right, but in the military under such circumstances we 'call' the traffic that is outside CAS (a la RIS). If the pilot requests avoiding action we give him a turn. Regardless, there is no clear definition of the seperation required.

TC_LTN
9th Oct 2002, 08:56
Interesting debate.

Just to point out that if I called all the traffic immediately adjacent to CAS in the Luton scenario on a summer's Sunday afternoon I would never get the closing heading in!

I guess it depends on the environment you are operating but I tend to be very selective about passing ANY traffic information on traffic outside CAS to traffic inside. One example, when I do make the call, tends to be when traffic is operating east of Stevenage at 2,400ft ALt outside CAS and I vector traffic onto a base leg from the LOREL Gate descending to 3,000ft Alt and pointing straight at it. I feel it is nice (but not required!) to pass some traffic information on the observed traffic especially in these TCAS sensistive days!

Any EZY/BAL/MON/RYR jockies have an opinion on whether this is useful or should I save my breath?

almost professional
9th Oct 2002, 10:40
tc
how do you find your operators and tcas-with us it is more and more the case now that if you dont tell them about transponding traffic, even if its known to you, they will sure as hell let you know (i've taken to giving as much primary only traffic info as I can-just to make a point-but thats just me!)

Whipping Boy's SATCO
9th Oct 2002, 16:50
TC, we have a similar problem with aircraft routeing from LAM direct for RW25. The 'gotchas' are normally helos tracking the BNN 133 radial hoping for a SVFR clearance into the CTR just north of Brent. The problem is that these helos often blunder on expecting a clearance that will never come despite being told to remain outside of CAS. Closest point of confliction is 8nm finals with approx 1nm and 500ft separation; I'm inside, they are outside on a 90 deg convergence!

Slaphead
10th Oct 2002, 10:15
alphaalpha,

I am current at Luton and Essex/Stansted and my reply to your comments would be;

I will always keep IFR traffic inside the lateral limits of CAS but it is not always possible to keep within two miles of the boundary. Luton and Stansted have similar problems as the example given by ATCO Two.

I never descend to less that 500 feet from the base of CAS but we routinely descend to the lowest available altitude above the base of Class A or D CAS. In the example given by TC_LTN, if you didn’t descend to 3000 feet on a base leg in the CTA then the inbound would be above the G/P. On 05 at Stansted you use 2000 feet in the CTA on the extended centreline for similar reasons and also sometimes to provide separation from following traffic if you are doing tight spacing.

If you contact me and advise me of a route which keeps you outside CAS then it will make no difference to my handling of IFR because, as already stated, you are deemed separated from traffic inside CAS and I will make sure that my IFR traffic stays inside. In some specific circumstances I may provide traffic information to IFR traffic inside CAS on traffic outside CAS but this is rare. Very occasionally IFR traffic will request information on traffic close to CAS if they have received a TCAS TA but most of the operators appear to understand the airspace around both airports.

If you request and are granted a VFR transit clearance then there is no requirement to provide standard separation, traffic information and/or traffic avoidance is all that is required. We routinely descend to 500 or 600 feet above operations inside CAS which are not in contact with us, for example the gliders at Halton and Dunstable if your doing Luton and the gliders at Hunsdon, North Weald and Weathersfield at Stansted.

In my opinion, if we were ever in the situation where we are required to keep IFR traffic inside CAS 1000 feet above traffic underneath CAS then the altitudes used inside CAS would stay the same and the base of CAS would be lowered. It would be difficult for a lot of departures from Luton, Stansted and, I would guess, London City to reach 1000 feet above the base of CAS and still comply with minimum noise routeings and noise abatement measures at the airports. It would also affect the altitudes used for arriving traffic and limit the amount of permissible operations within CAS such as gliding.

I understand the points made by the Duke and Bern Oulli regarding RAS but I haven’t had experience of providing RAS since we have been able to vector under RIS.

chrisN
10th Oct 2002, 10:50
As one of the glider pilots at North Weald and Ridgewell (and I sometimes visit Dunstable and Halton), where we fly up to the base of CAS, the last thing we want is that base being lowered to give 1000 feet of clearance. We have no problem with 500 feet. In practice, I have never known an airliner to be at only 500 feet above CAS base directly overhead because it would have to be right in the corner of CAS to do so at North Weald or Ridgewell. If that were to happen, I would not consider it to be a problem, but we would probably want to avoid the immediate area for a while to avoid the wake. We could live with that. I hope Slaphead and others would confirm if asked that airspace busts in Stansted and Luton CAS are rarely by gliders - for some reason, it seems to me that PPLs are the vast majority of such busts.

alphaalpha
10th Oct 2002, 14:16
Well, one GA pilot now understands a lot more about separation. Thanks, everybody.

My conclusions, which will become part of my modus operandi, are as follows:

a) It's OK to route close to the boundary of CAS, but separation from traffic inside may be less than desirable. So avoid being too close vertically and laterally unless for a specific reason, such as avoiding other hazards or because of high ground below.

b) Therefore in VMC keep the usual good look out -- But looking inside CAS as well as other directions.

c) In VMC, contact the (Class D) controller for FIS; this will allow mode C verification as a minimum to help with TCAS alerts, and will give the controller the knowledge that almost professional and ATCO Two would like.

c) In IMC definitely make contact and ask for RIS or RAS. If I'm in IMC just outside CAS, the traffic inside will probably also be in IMC, and close TCAS alerts in IMC are not good for anybody. If no service is available, don't get too close to the boundary.

d) It does seem that I'm making life harder for you by becoming known traffic, rather than remaining unknown (which you can 'deem' to be separated), but in this case, harder does mean safer for all. Although, I suspect Slaphead is talking common sense when he says he deems traffic outside CAS which has contacted him to be separated. [Slaphead - I assume you are talking about VMC?]

e) I will continue to request transit when it makes sense to do so. Both Luton and Essex seem to be much more willing to offer clearances than a year or so ago, something which I do appreciate. Some days and in some places I would much prefer to be in CAS than outside. LAM-BKY is much safer than LAM-BPK-BKY, even in good VFR.

Two questions still in my mind:

Do the London TMA controllers working the area close to EGLL want to hear from GA traffic just under the TMA base? I assume not, on workload grounds. (HD or 120.4 any comments?)

Should a better understanding of ATC procedures be a bigger part of GA pilots' training or information resource. For example, should this separation issue be covered in an AIC?

Finally, ChrisN, the On Track team will be reporting fairly soon, I believe, so we'll know more about the reasons for airspace busts. However, this is really off this thread and is a very different issue.

Warped Factor
10th Oct 2002, 15:27
alphaalpha,

Do the London TMA controllers working the area close to EGLL want to hear from GA traffic just under the TMA base? I assume not, on workload grounds. (HD or 120.4 any comments?)

Not on any of the Heathrow Approach or London Control frequencies.

But if you contact any of the other radar units in the area (Special, Farnborough, Benson, Northolt etc) and we see you on one of their squawks we can assume they have verified your height readout and are looking after you.

WF.

Slaphead
10th Oct 2002, 16:08
alphaalpha,

Re: your para c

You are of course welcome to call for a FIS but don't assume that you will be allocated a discreet squawk and have your Mode C verified, it is quite legitimate to provide a FIS without allocating a squawk. If you want to transit CAS you will be allocated a squawk and the Mode C will be verified but if you're VFR you won't be separated from IFR traffic although you may be allocated a route or level which takes you away from the arrival or departure track.

Re: your para d

It is one of the anomolies of the airspace in which we operate that anything outside CAS is deemed separated from operations inside CAS. In the example given earlier by TC_LTN, you can legally have IFR traffic inside CAS at 3000 feet pass overhead known IFR traffic underneath CAS at 2400 feet.

Bouncy Landing
14th Oct 2002, 22:33
I am heartened that controllers wish to have a call from GA operating close to their boundaries (Ive always understood this to be the case) but of recent I've had not such positive experiences:

Luton politely told me to get off their frequencey when I called to let them know I was heading north close to their western boundary; and Essex ignored my 3 calls when close to them in the LTN/STN gap (and no it wasnt wrong frequency or radio failure - I heard them ignore someone else and a few minutes later Lakenheath received me strenght 5).

In both cases it did not make much difference to me as it was good VMC etc and my calls were really for their benefit - does'nt encourage one to maye a voluntary call another time tho......

alphaalpha
15th Oct 2002, 08:20
Bouncy:

My recent experience is

Friday - two IFR flights just outside & to west of Luton, received RIS (& cleared for CTA transit which I didn't need)

Saturday: IFR just outside E Mids & Birmingham. Received RIS.

Sunday: VFR just outside E Mids. Received FIS plus very useful traffic info near to LIC -- without asking for upgrade to radar service.

Saturday and Sunday: VFR up & down the Manchester low-level corridor & under the southern part of the Manchester TMA. Received FIS from Manchester approach with useful info about other corridor traffic.

Based on the r/t traffic, the controllers seemed moderately busy, but not excessively so. On Sunday there were a few other GA-sounding flights also receiving service from E Mids & Manchester.

All in all, excellent service!

BTW, I've never been ignored by Essex, but I have been told to standby (for around 5 minutes).

almost professional
15th Oct 2002, 09:49
alphaalpha
sunday morning or afternoon near LIC?

alphaalpha
15th Oct 2002, 12:13
almost professional:
Sorry, I can't remember exactly. On Sunday, I flew Barton/WHI/LIC/Bourn and was aiming to get back before the bad weather arrived from the south-east. It would have been circa 12.00Z at LIC. Callsign is GYBAA (hence my Pprune handle). Did I speak to you?
AA.

almost professional
15th Oct 2002, 12:44
alphaalpha
indeed you did, at least on the way out-did I remember to tell you about the gliders at cross hays?

alphaalpha
15th Oct 2002, 13:08
almost professional:
Yes, you did, and thank you.

On Sat I was IFR routing NW via Lichfield circa 1300Z under your RIS. I requested to route W from LIC to avoid Cross Hays. You quickly handed me on to Birmingham. A nice reminder to watch the CAS.

On Sun, returning, I was VFR and under FIS. You requested my position, presumably to confirm what you suspected, warned me about unknown tfc close to LIC and also mentioned the gliders. Above and beyond the call of duty as you were providing only FIS (and the other traffic was not working you), but the sort of thing that the GA pilot appreciates.

Anyway, that's why I said 'excellent service.'
AA.

almost professional
15th Oct 2002, 13:30
AA,
glad to have been of service, great to know its appreciated. certainly my watch, and i like to think the rest of the unit, try to help where we can, despite the problems this year of being short staffed and dealing with a large increase in scheduled IFR traffic. Speak to you again sometime,

AP

:D

Bouncy Landing
15th Oct 2002, 22:02
AlphaAllpha

Thats what I'd have expected, guess I was just unlucky on those occassions. Thanks for balancing!