New guidance on unknown traffic in Class D

[NorthSouth]

Seems to me the recent ATSIN clarifying the advice to be given when unknown primary radar contacts are seen in Class D airspace opens a can of worms - it seems everyone's been operating for years on the misapprehension that traffic info should be given - and avoidance where necessary. Now it's no traffic info or avoidance unless you know there's an aircraft lost, infringed your airspace or had radio fail. But who's going to take that risk?

NS

[Spitoon]

Don't see the problem.

Action on unknowns in Class D airspace is:
Neither avoiding action nor traffic information shall be passed unless radar derived or other information indicates that an aircraft is lost, has experienced a radio failure, or has made an unauthorised penetration of the airspace.

You are assuming that any primary target that you see within the CAS boundary is inside the airspace. Apply common sense just as you would before on any NMC targets - have you really given avoiding action on all the NMCs that you've seen?

[2 sheds]

If your Class D airspace is a CTR, then by definition it extends upwards from the surface. Therefore, any radar return (not a "contact", please) within the lateral limits that cannot be associated with known traffic must be within the airspace (or the airspace above it) and therefore must be considered to be lost or making an unauthorised penetration.

In the case of a Class D CTA, in the absence of other information, unknown traffic would be assumed to be obeying the law and be flying below the CAS. However, if it were squawking on mode C and the level readout, albeit unverified and possibly corrupt, would put it inside the CAS, I would suggest that, again, that constituted evidence to suggest lost or unauthorised penetration.

[Standard Noise]

Yep, pretty much agree with 2 sheds. However, I always tell the inbounds about the traffic's position and add "no mode charlie but believed to be below the base of CAS." I'm afraid the ATSIN won't change me there.
Saves the poor sod upstairs from having a pink fit when his inbound at 5.5D tells him a tiddler has just passed in front of him at a similar level. (Our CTR extends 5 miles out from the field with a stub E&W from 1500' upwards)

[Chilli Monster]

If your Class D airspace is a CTR, then by definition it extends upwards from the surface. Therefore, any radar return (not a "contact", please) within the lateral limits that cannot be associated with known traffic must be within the airspace (or the airspace above it) and therefore must be considered to be lost or making an unauthorised penetration.

Not necessarily. What about CTR's which have an upper limit and are class 'G' above?

[Turn It Off]

I think that any airspace which has a latarel confine, an pper or lower limit, that, any primary return is to be assumed to be either above or below.

However, if it were squawking on mode C and the level readout, albeit unverified and possibly corrupt, would put it inside the CAS, I would suggest that, again, that constituted evidence to suggest lost or unauthorised penetration.

Agree totally, if its got Mode C use it, just lob in the unverified bit with the traffic avoidance.

TIO

[HEATHROW DIRECTOR]

<<Now it's no traffic info or avoidance unless you know there's an aircraft lost, infringed your airspace or had radio fail. But who's going to take that risk?>>

That's always been the rule with Class A airspace so what's the problem?

[DFC]

So if I don't bother to call for clearance to transit a zone, have a perfectly good radio and to avoid snoopy radar, I turn off the mode A and C, I will have to keep a bloody good lookout because the ATC will not try to keep pesky jets out of my way. I am not lost and I don't have a radio failure.....I just can't be bothered!

Better still, if the zone has calss G above, I can leave the mode C on and when the heavies call, tell them that the mode C was discovered to be U/S after the flight and is now fixed!

Seriously, I can't think of an occasion where ATC would intentionally point an aircraft at a radar return which could be within their airspace without atleast warning the pilot.

If the UK had the ICAO VMC minima for Class D airspace i.e. aircraft would have to be 1000ft vertically and 1500m laterally from cloud then I would probably find it easier to accept the situation............most zone infringements are by flights under VFR. The reason being that as I exit the base of a cloud the closest VFR aircraft would be 1000ft below. However, in the UK Class D, the VFR flight could be hugging the base of the cloud!

When in Class G we operate above 3000ft i.e. in the FLs for as much as possible when IFR for the very reason that VMC flights have to keep well away from clouds at those levels.

Regards,

DFC

[DFC]

This post has got me thinking.

Can any ATS person tell me.......if the ICAO VMC minima for Class D were set because VFR are not separated from IFR i.e. is the intention to keep VFRs well away from cloud so that the IFRs can spot them after popping out of the cloud at 250Kt..........or is there another reason why the minima are such?

Regards,

DFC

[Tower Ranger]

I`d suggest that if you still work in the dark ages of primary only as we have you surrounded by D,E and G airspace then your gonna pass traffic info and make sure th blips don`t merge. Regardless of whether you think its one of the lighties you`re talking too you`d be a bit daft to assume the ident.
Is the definition of " known traffic " still the same?

[Turn It Off]

DFC,

This doesn't really answer your question fully but it might help a little.

For a pilot to maintain VMC they must be 1000ft below cloud, 1500ft horizontally from cloud. Whether or not this is to help people gain visual reference with eachother when an IFR a/c breaks cloud I don't know.

However, the spanner in the works,

Below ALt. 3000, an aircraft with a TAS of 140kts or less only has to remain Clear of Cloud and In Sight of Surface, which means that VFRs can get out in very very low cloud, which would give IFR a/c little chance of spotting something, especially if traffic info hasn't been passed.

I'm at a unit based in Class D and we try and provide, where possible at Least standard seperation between VFR and IFR. Generally (Not always) we will aplly a procedural seperation ( VFR not above 1500ft, IFR descending to 2500ft), in order to provide maximum protection to all a/c involved.

Hope that helps a little

TIO

[edited 15:54 23/11/2004]

The above 'caveat' to the rules does not exempt a pilot from 5, and the met vis must be 5000m, below that a Special VFR clearance would be issued.

[DFC]

TIO,

Taking your Class D as an example.

The ICAO VMC requirement is for an aircraft to be 1500m horizontally and 1000ft vertically from cloud regardless of height.

This means that to fly VFR at 1500ft, the cloud would have to be 2500ft or above.............unless a special VFR clearance is given.

Thus under ICAO rules, there is a provision made for the IFR guy just inside the base of the cloud (unable to see the VFR guy) to be 1000ft above them.........unless the VFR flight gets a Special VFR but then they will be ATC separated.

Since ICAO specify a minimum height of 500ft above the surface, it is impossible to get VFR when the cloud is below 1500ft.....a well defined cut-off!

Taking the UK position a VFR pilot can hug the base of the cloud literally feet away from the IFR traffic just above........all within the UK rules.

Thus as I see the position, the UK CAA has taken away an inherent safety measure included in the Class D ICAO airspace without making any requirement........other than relying on ATCOs to operate in accordance with some moral code (if they choose). This in turn makes the VFR pilots complain of unnecessary restrictions because after all ATC are not required to separate them from other traffic in class D.

Under ICAO the clear of cloud in sight of the surface only applies in class G.

Classic case of passing the safety buck?

Regards,

DFC

[HEATHROW DIRECTOR]

<<other than relying on ATCOs to operate in accordance with some moral code (if they choose).>>

You can't operate under a "moral code" in busy airspace - it just isn't possible. When unknown traffic appeared in side the London Control Zone we used to take avoiding action - after checking with adjacent ATC units, etc. However, unidentified traffic in the London TMA was totally ignored and assumed to be below the level of our traffic.

If you ever get the chance to watch an ATC radar on a sunny Bank Holiday you'll understand the problem. Approaches into Heathrow pass over, or close to, half a dozen or more light aircraft fields and blips merge - known in Class A versus unknown outside CAS - hundreds of times a day.

If traffic info or avoiding action had to be given the system would collapse.

[PPRuNe Radar]

I don't see your point DFC.

In Class D in the UK, the ATCO would almost without exception pass information on the VFR (he has to be in contact and obey ATC instructions after all) to the IFR. Almost without exception, they would probably build in some form of separation too (although not formally required).

In Class G under ICAO (as well as the UK), neither aircraft need be in contact with one another and the IFR can blissfully pop out of cloud unannounced straight in to the VFR hugging the cloud.

So are you are saying that a Class G collision under ICAO doesn't really matter and is just one of those things, whereas a collision of the same geometry in UK Class D does and it must be the CAAs fault ?? Both would end up with dead people.

Far from removing a safety measure, UK Class D actually adds safety compared to Class G surely ??

[NorthSouth]

DFC:

I can't think of an occasion where ATC would intentionally point an aircraft at a radar return which could be within their airspace without atleast warning the pilot

And yet that's just what the CAA is telling controllers in Class D to do in the latest 'correction' of MATS Part 1.

[bookworm]

So are you are saying that a Class G collision under ICAO doesn't really matter and is just one of those things, whereas a collision of the same geometry in UK Class D does and it must be the CAAs fault ?? Both would end up with dead people.

The point of controlled airspace is that it is placed where it is justified by traffic density and ATS needs. In the ICAO scheme, class G would not be used in areas where such a collision was likely. The very existence of class D implies that there is increased likelihood of collision if other measures aren't taken. One of those measures is to require VFR traffic to operate with minimum separation from cloud, another is to require them to be in touch with ATC.

The current UK exemption for class D takes away the former. While traffic information is useful when it gives the IFR traffic an opportunity to see and avoid the VFR (and vice versa), there is, in the UK scheme, not guaranteed that the aircraft will have the opportunity to see each other before the moment of collision.

In essence, I agree with DFC. The modification to the class C/D/E minima was introduced without much consideration for the consequences after someone realised that the minima as originally drafted as Rule 25(b) made it operationally impossible to fly circuits at 1000 ft in class D with the cloud base below 2000 ft.

[DFC]

Radar,

Bookworm has hit the nail on the head.

I would also add that the clear of cloud bit only applies at/below 3000ft in class G. Thus taking ICAO airspace, an IFR flight in IMC operating at a level equivalent to 4000ft AMSL or more and then entering a zone for the instrument approach can be satisfied that they are atleast 1000ft vertically and/or 1500m horizontally from all VFR flights up until they become visual........and then they have time to spot the traffic..........which is why the visibility requirement is 5Km in D every height and G above 3000ft and we are limited to 250Kt..............all to give us a chance to operate the see and avoid.

Bookworm,

It is perfectly possible to fly circuits when the cloud base is 1500ft and the circuit height 1000ft under ICAO...........operate special VFR and the tower use reduced separation in the vicinity.

Regards,

DFC

[bookworm]

It is perfectly possible to fly circuits when the cloud base is 1500ft and the circuit height 1000ft under ICAO...........operate special VFR and the tower use reduced separation in the vicinity.

Yes, in the simplest case, it's clearly possible to fly SVFR if you're the only aircraft around. But if there are more than one, doesn't even "reduced separation" between SVFR flights place a rather heavier operational burden on ATC than simple VFR in the circuit?

[PPRuNe Radar]

Nope, you still have me lost.

It's 'OK' for you not to have 'separation' from traffic in Class G - the flawed big sky theory I suppose. But in Class D where traffic is KNOWN and given to you, hence at least providing you with information on something you can't see and so can adapt your profile if you so wish, then it's NOT OK ?? You seem to infer that Class D is less safe than Class G.

Class G can be just as busy and concentrated, if not busier, than many bits of Class D. But of course without the need for anyone to be in contact or their intentions known.

The argument about the below 3000' bit (as if it doesn't matter in Class G) is also a red herring as it is very applicable to many instrument approaches (South of the Lakes and outside Wales anyway), so you could still encounter a VFR as you pop out of cloud there quite legally below 3000' whilst following the chart.

Still, at 250Kts, you might get his number as you plough into the side of him ??

If anything, I would have expected pilots to be more worried about fighting to raise the limits for flight in Class G, rather than slating reduced limits in airspace where there is some modicum of 'control' and information.

[DFC]

Radar,

According to the rules, we get the same separation from VFRs in Class D,E,F and G............None!

Ideally we would never complete an instrument approach in anything worse than class E.

Unfortunately, in the UK we have to from time to time complete an instrument approach or for a period of time fly IFR below 3000ft in Class G..........in those cases we require a minimum of RIS..........and the CAA for it's part asks VFR pilots to avoid the let down areas marked on the chart. Thus a mid-air in Class G would be most likely with a pilot who ignored CAA advice to avoid the published let down area of an approach permitted to be made in class G airspace where class E would be far safer.

But the VFRs in Class G are not the real danger - the real danger comes from other IFRs who can be in the same cloud and not talking or squalking!

I believe that places like Filton and Farnborough, Southend, Oxford, Coventry etc etc should all have Class E airspace and appropriate VMC requirements.

The way that I see the current situation is that the CAA has reduced safety by not keeping the ICAO VMC requirement in Class D and at the same time placed an extra burden on the ATC units which causes extra workload and reduces IFR capacity a little but greatly reducing VFR capacity. This causes frustration to the average VFR pilot because they don't understand why in the UK thay are refused entry to airspace where they are not separated from anything else.

If we were to create a fuss or make a point, we would request avoidance of every VFR flight mentioned in UK class D because the reduced VMC minima makes visual avoidance more difficult that ICAO say it should be.

-----

Bookworm,

Yes, it could create extra workload for ATC because afer all they then have to separate the Special VFR flights from the IFR Arrivals/departures..........but isn't that the whole idea.....to separate aircraft who would be a collision risk in cases where visual avoidance is unlikely.

In the current situation, a controller can legally allow a VFR PA28 to join final approach just under the cloud base and 1nm ahead of a B737 on final and meet all the requirements by issuing traffic information to both aircraft. That may be legal but there isn't a sane person that will stand up and say that operating in accordance with UK procedures for VFR in class D is safe..............If it isn't safe then the CAA are required to take action before an accident happens.

OK requiring that same PA28 to be 1500m further away from the cloud or 1000ft below it probably won't make a perfect situation..........but it gives us a fighting chance to see and avoid....which after all is what we must do in class D.

A quick search will find a long thred about orbiting VFR flights downwind...........a case of ATC trying to separate aircraft where no separation is required. AOPA and GASCO are up on their high horses about the whole orbiting thing but have ignored or failed to spot the whole VMC issue.

----

When delaing with Special VFR, most UK pilots think that is operates purely on visibility basis - because that is what they learn at school. But they fail to understand that special VFR may be required because of proximity to cloud even if there is 50K visibility.

Regards,

DFC