Look Out for VFR Pop-Up Traffic

Explain this to me.

I was on the cockpit jumpseat as we were descending into San Francisco International yesterday. Inflight visibility was good, though the sun was blinding as it sank towards the western horizon.

stock photo

Can’t see much in this direction. (Stock photo.)

Suddenly, Norcal Approach said, “Airliner 521 Heavy*, expedite a right turn, heading 280.” The Pilot Flying complied. A second and a half later, Norcal said, “Airliner 521 Heavy, turn further right immediately, heading 300.” What?!

There it was on the TCAS (Traffic Collision Avoidance System) display–a traffic symbol at 11 o’clock and 5 miles, shifting left, 200 feet below us as we descended through 11,700 feet. Couldn’t see it outside though. The sun was wiping out the view in that direction. Apparently TCAS wasn’t too concerned about it because we didn’t get an aural traffic alert from the system.

The Pilot Flying rolled our aircraft wings level on a heading of 300. The traffic symbol on the TCAS slid safely to our 9 o’clock position and 5 miles, heading the opposite direction. Finally, Norcal said, “Airliner 521 Heavy, VFR traffic your 9 o’clock, Mode C indicates 11,500, no factor.” Ah hah. Good to know.

So here are my questions.

1. What is the thought process that leads a pilot to conclude: It is safe to fly VFR at 11,500 feet, in one of the busiest arrival corridors in the country, and not get in contact with ATC?

By the way, the arrival corridor we were using is not a well-kept secret. It is one of several clearly depicted on the VFR Flyway Planning Chart for San Francisco.

2. Why didn’t ATC give us an earlier alert that traffic was approaching?

There are several possible answers for both of these questions. What is your opinion on this?

The Takeaways:

It is perfectly legal to fly VFR anywhere outside of positively controlled airspace and not get in contact with ATC. That’s how many pilots routinely operate. I have always strong recommended that you get in touch with ATC for VFR flight following.

VFR flight following gives you an extra margin of safety when flying through heavily trafficked areas. Not only does ATC’s radar help you clear for traffic, maintaining contact with ATC helps the controller stay updated on your intentions. Working with ATC puts you into an information loop that helps you and other pilots keep safely separated.

*Airliner 521 Heavy is a fictitious call sign. The story is accurate to the best of my recollection.

{ 4 comments… read them below or add one }

O. Mahdi October 19, 2015 at 6:46 pm

Perhaps it’s due to the classification of the airspace? I know that in some airspace classes it’s not the responsibility of the ATC to separate aircraft at all.


JeffKanarish October 19, 2015 at 8:15 pm

Mr. Mahdi,

Thank you for answering.

You are correct that ATC is not required to provide separation between VFR aircraft. ATC is always required to keep IFR aircraft separated from any other aircraft, VFR or IFR, in all airspace classifications.

Here is the central issue. My question asks, why would any VFR pilot think it is safe to fly in the middle of an area that is packed with high speed jet traffic and not get in contact with ATC. It may be legal to do this but that doesn’t make it an intelligent choice.


O. Mahdi October 19, 2015 at 9:49 pm

Oh, my apologies, I misunderstood your question. To be quite honest, at this point, I have no idea if there’s an actual logical answer to that question other than being somewhat irresponsible.

Maybe because that pilot relays too much on TCAS equipment that exist in jets, and therefore believes that he’s going to be safe no matter what due to TCAS. Or maybe because the VFR pilot knows that the ATC is going to separate IFR aircraft from him regardless of whether he makes contact with ATC or not, so he just decides not to.

I don’t know if these were the guesses you’re looking for, but I really can’t think of any other reason for taking such course of action, and personally, I wouldn’t consider such action as safe, even if it’s legal. For me, it’s the same as doing touch-and-goes in a C172 at JFK at rush hour. It may be legal, but I wouldn’t consider it very safe.


JeffKanarish October 19, 2015 at 11:36 pm

Mr. M,

No apology necessary. I’m glad to hear your ideas.

I’m sure you are correct in the case of some pilots. Relying on other aircraft to keep away is probably how some pilots approach the problem.

It could also be that some pilots are simply not aware of the potential danger of flying in or near lanes of high-speed traffic. Or, maybe some aren’t even aware those lanes exist. We’ll never know for sure.

Best wishes to you, and keep in touch.



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