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.
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?
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.