"Citation One Charlie Mike, traffic twelve o'clock, five miles, southwestbound, level six thousand, a Gulfstream," transmitted the controller. "Uh, One Charlie Mike, yeah, we got 'em on TCAS," responded the pilot. A moment later the controller transmitted an updated traffic advisory, "November One Charlie Mike, that traffic's now one o'clock and three miles, six thousand." The Citation pilot responded, "Charlie Mike's got 'em on the box." I would imagine at this point the controller rolled his eyes and went on about his business, monitoring his sector and watching for traffic conflicts. What the Citation pilot didn't understand was why the controller was issuing him a traffic advisory and what the controller needed to hear to take further action.
Situations like this hypothetical event occur everyday. In this case, imagine that the Citation was level at seven thousand, his course converging with the Gulfstream one thousand feet below. The Citation needed lower because he was nearing his destination. The controller must separate the aircraft by three to five miles laterally, depending on the type of radar being used. If the airplanes are closer together than this in terms of lateral distance, the controller must separate them by one thousand feet vertically (or less in some situations). However, when visual meteorological conditions exist the controller may employ visual separation when the airplanes see each other. Have you ever heard a controller say to you, "Maintain visual separation with that traffic"? That means he's using visual separation procedures and the vertical and lateral spacing requirements are waived. When visual separation is being used as long as no one exchanges paint, controllers (and pilots) are happy. In order for a controller to employ visual separation, though, the pilots of the conflicting aircraft must report each other in sight. In the case of the Citation, the controller was attempting to initiate visual separation in order to expedite the airplane's descent as opposed to waiting until the Citation was three to five miles on the other side of the Gulfstream below. But since the Citation pilot didn't make much of an effort to find the other traffic, he denied himself the benefits of visual separation and the increased flexibility it unlocks.
You see, controllers follow complex sets of rules (just like pilots) that guide and dictate their decisions. When a controller issues a traffic advisory in an effort to initiate visual separation procedures, his rules tell him that the pilots must see each other with their eyeballs before they're permitted to penetrate each other's separation bubbles. Seeing another aircraft on a Traffic Collision Avoidance System (TCAS), or Traffic Information/Advisory Service (TIS/TAS) in the case of a light airplane, is not sufficient for the allowance of the reduced spacing visual separation provides. The FAA only trusts your eyeballs for that. When you tell a controller you've "got them on TCAS" you're wasting his time. He'll just filter those words out and translate them into his own controller language: "He doesn't have the other traffic in sight. That means I can't use visual separation." TCAS isn't approved for use in visual separation because, after all, it's not visual. It's a computer system. The controller already knows you probably see the other guy on TCAS, and he's not interested in that. He's only interested in whether or not you see him out the window. That's what is operationally significant to him. Think of it this way, imagine you said to the controller, "We've got 'em on TCAS." The controller then replied, "Yeah, and I've got you both on radar. That's not what I'm getting at." If two big, fast, shiny flying machines are going to whisk past each other in flight, the FAA insists that the pilots must primarily be relying on their eyeballs and not technology. That makes sense.
Remember, everything a controller does is for a reason. He's at work. He's got a job to do, and he's being guided by logical rules and procedures at all times. Whenever a controller gives you an instruction, try to figure out the reason for the instruction. Be curious about the operational significance of what he's asking of you. Whenever a controller talks to me on frequency, my mind automatically envisions him sitting in front of a big black radar scope with green blips and data tags watching for traffic conflicts, planning ahead about what each aircraft needs and keeping it all straight in his mind. Controllers call this "the flick." It's a fun term for situational awareness. Taking a tour of an air traffic control facility can be an amazingly beneficial activity for any pilot. Learn as much about the air traffic control system as you can, and it will serve you more pleasantly and effectively. And next time a controller gives you a traffic advisory, make both of your lives easier and find the other aircraft with your eyes. Your aviation medical examiner didn't certify your vision for nothing. You've got the gift of sight, use it!
