How would ATC try to establish contact with a VFR craft?

Question

Example: I'm in a 172 tailed N1234A, on a pleasure hop between Hicks Field and Addison, circling around DFW International to the north, flying at 1500ft within DFW's Mode C veil under VFR (so I'm squawking 1200). The approach direction for the day also happens to be the north (this is common; prevailing winds in the area tend to be southerly). I'm staying outside DFW's airspace and therefore have not checked in with DFW Approach.

As I'm about to pass underneath "Area B" of DFW's space (which begins at 2000ft between 10 and 13nm from the airport sweeping across the northern approach), there is a 747 approaching low in the class B umbrella. It will pass above and in front of me, but still too close for their comfort, and so ATC wants to verify that I see the jumbo out my left window and perhaps suggest I descend.

Questions:

1. Was flying under the approach traffic of DFW my first mistake? Should I instead be heading around south (which would be a really big detour as I'd need to avoid Love Field's portion of Class B) or just contacting DFW Approach for clearance through Class B space?

2. Am I in the wrong for not having made prior contact with DFW Approach or Fort Worth Center in these circumstances, even though I'm operating VFR in class E/G space?

3. Should I even be this close to Class B in the first place (I'm 500 feet below it and 2 miles outside the surface footprint)? If not, what's a better altitude and range for me to have planned for? Outside 13NM from the airport, I'd be under Area H which starts at double my altitude, 3000 ft, but would also require me to enter or avoid Alliance's Class D space, and it'd take me quite a bit out of my way (since it's just for fun and logging hours, I might as well just touch and go at DTO if it'll be this much hassle to avoid DFW).

4. Would DFW or FW Center even bother trying to inform me of the situation, assuming I stay safely underneath Class B space and the 747 stays safely in it? One would think, being in contact with the 747, they could simply tell the jumbo to maintain minimum 2500 or 3000ft until 10nm out to maintain 1000ft minimum vertical separation, but my experience with boats says that if someone should yield right of way in this situation, it's the smaller craft (me).

5. Here are the title questions. How would DFW attempt to contact me? What frequency would I be expected to be tuned to? The emergency frequency is of course 121.5, but during normal flight along this path I could conceivably be listening to Fort Worth Center (122.65), DFW Approach (124.3), Addison ATIS or Approach, etc.

6. What would they say that I'd be expected to respond to, and how should I respond? I'm guessing they'd say something to the effect of "unknown VFR craft bearing 350 range 12 altitude 15, acknowledge and identify".

Answer 1

Long story short, ATC has no reason to contact you but if they were to try they'd probably use 121.5 (see below). You're not in their airspace and the whole purpose of that airspace is to ensure separation, so as long as you remain clear of it they won't be concerned about you although they'll probably report your position to the 747.

As for your specific questions:

1. That's your decision as PIC and no one else can make it. But I wouldn't spend much time in a zone where I'm at high risk of a wake turbulence encounter.
2. No, there is no requirement for you to be in contact with ATC in that airspace so you're not wrong. It would be good to get flight following if possible, but that's optional and might not be available anyway.
3. It's hard to say what "too close" means and it could change depending on the time of day, if you're thinking about traffic. Again, this is something that you as PIC have to determine.
4. They won't try to contact you since you're outside the class B and they have no reliable way to contact you anyway. And considering wake turbulence again, "too close for their comfort" is probably more like too close for your comfort :-) Aircraft size isn't a consideration for right of way (see 14 CFR 91.113).
5. They won't for the reasons above. And they also can't know if you have a working radio, which frequency you're on etc. But they would probably try 121.5 because a current FDC NOTAM states that you should be monitoring it if you can:

ALL AIRCRAFT OPERATING IN UNITED STATES NATIONAL AIRSPACE, IF CAPABLE, SHALL MAINTAIN A LISTENING WATCH ON VHF GUARD 121.5 OR UHF 243.0.

The AIM also suggests and encourages all pilots to monitor it (e.g. section 6-2-4).

6. It's hard to say, the FAA's ATC instructions don't cover this situation (or I couldn't find it). But giving a specific bearing is unlikely (a bearing from what?) because you might not have the equipment to verify it so perhaps "12 miles north of DFW at 1500ft" would be more likely for the position part.

Of course, if ATC really, desperately, urgently needs to contact you - like if you fly straight through the class B without a clearance - then they can always request an interception. That would really ruin your day, so monitoring 121.5 if you can is probably a good idea.

Answer 2

Normally they wouldn't even try to get in contact with you. It is easier and probably blocks less time on the frequency to talk to someone they have established contact with than to someone who they don't know which frequency he's on. What you said in point 4 is correct, they don't have control over you as you're VFR and you're not even in their controlled airspace. Bigger aircraft don't have right of way over smaller aircraft. FAR-AIM Sec 91.113

What they will probably say to the 747 is something like "American 123, traffic, 3 o'clock 2500 feet, same direction, type unknown."

If AA123 acknowledge that they see you, "American 123, maintain visual separation", otherwise "American 123, maintain 3000 feet for traffic"

Answer 3

In practice they'll ask at approach sector frequency, "Regional to N123AB, are you on frequency?" My side of DFW is south and the approach is Regional 135.975. Although it's very rare in DFW and more common in Austin where confused pilots are typically at 119.0 anyway.

Answer 4

Pondlife's answer is excellent, but to expand on #1, anytime you are flying under a class B/C shelf, it is a very good idea to be talking Approach. There are usually a lot of planes down there squeezed into a very small space, so an extra set of eyes is invaluable.

In this specific case, Addison's ATIS will say to contact Approach--not Tower--on initial contact due to the airspace shape and traffic levels. Since you're going to have to call them anyway, you might as well do it as soon as you're off Hicks. They will probably clear you through the Bravo and vector you over the top of DFW, possibly without you even asking, which also avoids your wake turbulence problem and saves you time/money. Everyone wins.