IFR Separation from unknown VFR traffic

[Jumbo Driver]

I have a question for you ATCO experts, based loosely on a reported occurrence to a colleague in my local area.

You are controlling Radar Approach in a Class D Zone, which has an overhanging CTA extending out beyond the Zone limits. Within that "overhang" area you see what appears to be VFR traffic (squawking A7000 but no Mode C) which is outside the Zone but within the lateral confines of the CTA. The chances are that this traffic is within the Class G area beneath the CTA but, without Mode C, you cannot be sure as the traffic is not working your frequency. You then have an inbound IFR (Identified Mode A, verified Mode C) to your instrument runway and its normal track will conflict laterally with the VFR traffic. What do you do?

As you cannot be sure of vertical separation, do you vector your inbound IFR traffic around the A7000 traffic, to ensure horizontal separation, or do you make the assumption that the A7000 traffic is OCAS and maintain only vertical separation with the base of your CTA at that point?

I have looked through MATS Part 1 for guidance (vide Sec.1, Ch.5, para.14) but cannot find the answer and I am guessing that the principle is such that it wouldn't be in the local MATS Part 2 (to which I wouldn't have access).

Can someone please tell me how this is dealt with in practice and point me in the direction of where guidance is to be found?


Anticipatory thanks

Jumbo Driver

:)

[radar707]

Unless the unknown traffic is believed to be lost, has experienced radio failure or believed to have infringed controlled airspace then no action is taken as it is deemed to be outside controlled airpace and as such no separation is required or traffic information to be passed.
Personally I would advise pilots of IFR traffic that the contact is there but believed to be outside controlled airpace.

MATS pt 1 section 1 chapter 5 page 13 14.2 refers

[Chilli Monster]

As class 'D' is deemed to be a "known aircraft" environment then it is assumed that the A7000 is in class 'G' below the class 'D'. Aircraft outside CAS are deemed to be separated from aircraft inside class 'D'

HOWEVER

As per the reference you looked at:

If radar derived, or other information, indicates that an aircraft is lost, has experienced radio failure or is making an unauthorised penetration of the airspace – avoiding action shall be given and traffic
information shall be passed.

Other information includes "a feeling in your water" ;)

However, even if you believe it to be outside CAS - you never let the blips merge - just in case!

[throw a dyce]

Also I have given a blind call to the 7000.Quite often they are monitoring the frequency in this neck of the woods.It's a classic situation practiced in the TRUCE training.

[Jumbo Driver]

Thanks, guys. Prompt and informative - as usual !



JD

:)

[normally right blank]

...and suddenly the "blip" comes up on the radio, when you call him out..:)

[London Mil]

As others have said. I must admit, it has been a number of years since controlling in a CTR, but I have a vague recollection of something along the lines of "if the IFR traffic is within 1000ft of the vertical limits, call the conflictor and, if requested, provide avoiding action" (that may have been something to do with a 7000C outside the CTR/CTA). I'm sure someone will be along soon to confirm my insanity.

[ATCO2]

Hi,

I have a simmilar question. What to do in TMA class E airspace, where VFR is not supposed to have even radio. They fly with no squawk on or if they have it on Mode C is not verifyed. I know that they have a radio but they operate in TMA class E with no obligation to call anyone. In that TMA, what I have seen, many IFR traffic is vectored to the ILS approach. ATCOs there pass traffic info as unknowen traffic and do a lateral separation with unknowen one. I think they are correct.

I would like to hear your opinion about this.

Regards,

ATCO2

[av8boy]

Ah. Flashback.

I was a controller at this particular facility (what used to be Los Angeles TRACON) when it happened.

http://amelia.db.erau.edu/reports/ntsb/aar/AAR87-07.pdf

It's the AeroMexico 498 midair with a Cherokee over Cerritos, California in 1986. The DC9 was on approach to LAX and the Cherokee was VFR inadvertently in (what was then called) the TCA. This accident proved the point that the 30-mile "Mode C veil" was an excellent idea.

In this case the TCA overhung lots and lots of non-Mode C traffic. One of them, the Cherokee in question, was not below the TCA. He was in it, crossing the finals for the 25s. He hit the tail of the DC9 and everybody died.

Like Walt said at the time, the non-Mode C traffic looked like an anthill, and "when the elevator door opens you expect to see an elevator." In other words, you expect the VFR guys to stay where they're supposed to be. Of course, there was no elevator on this day. He's never been the same. Good guy too.

:(

Dave

[radar707]

ATCO2, in the scenario you suggest, our book says:

Pass traffic information unless the primary function of sequencing and separating IFR flights is likely to be compromised
If a pilot requests avoiding action it shall be given to the extent determined by the radar controller
Give avoiding action unless radar derived or other information indicates that an aircrft is lost or has experienced radio failure

[ATCO2]

Hi,

Thanks a lot for your comments. I appreciate that.

Regards,

[tribekey]

Jumbo driver
At a certain south coast pair of airports where the airspace is exactly as you describe this situation occurs several times a week(sometimes several times a day). Chill Monster's answer is spot on.Allthough, technically , you can ignore the blip you'd be mad to let the blips merge, just in case it isn't below the CTA.

[Jumbo Driver]

tribekey, funny you should mention that certain neck of the woods ...

No names, no pack drill - it wasn't me, incidentally! However, there's a good chance you may know the aviator who has (unwittingly) prompted this thread ...



JD

:) :)