Now those see-in-the-dark controllers with their big radar dishes are watching over me the same as they do for the fast- and high-flying pros. Anybody gets close to me and the controller will spot it, ring me up, and call out the bogey before it becomes a problem. All this IFR-style traffic separation comes without having to pay any of the restrictive "costs" of flying on an IFR clearance, such as having to adhere to specific altitudes and courses when maybe I'd rather do something different. Is this a great country for aviation or what?
Yes, as a matter of fact it is - but despite what some seem to think, VFR traffic advisories are not quite the same as IFR-style traffic separation service, nor is it as "free" as it might seem. The fact that there is some confusion surrounding VFR traffic advisories was made clear to me by a comment made by a local pilot at a recent briefing involving the manager of the air traffic control tower at our airport.
The tower chief had finished his presentation and was taking questions. One pilot raised his hand, then told of having a close call with another airplane while flying VFR. The pilot had requested and was granted ATC traffic advisory service, and he had been squawking the discrete transponder code given him by the controller. Why, he asked our tower chief, had that airplane passed so close without so much as a word from the controller? (He didn't say what "close" meant.) Should he call the ATC facility to complain?
I don't know if he called or not, but if he did it's likely he was given a telephone short course in VFR radar advisory services. The lessons are found in the Aeronautical Information Manual (AIM), Chapter 4, Section 1, which details air traffic services available to pilots. The take-home message in the AIM discussion is the last sentence in the introduction to the section: "This service is not intended to relieve the pilot of the responsibility for continual vigilance to see and avoid other traffic."
In other words, we cannot totally rely on airplane transponders, air traffic control radar, and air traffic controllers to keep us from colliding with another aircraft. Even if we are provided with traffic advisories based on transponder information painted on a radar scope (or, increasingly in ATC facilities, a computer screen) the primary responsibility for scanning for traffic and avoiding conflicts rests with the person flying the airplane.
But, wait a minute. Why shouldn't we be able to place our complete collision-avoidance trust in the ATC system, even when flying VFR? After all, keeping aircraft from colliding is the basic reason our air traffic control system exists.
It's true that when an airplane flying on an IFR flight plan is in instrument meteorological conditions - in the clouds, essentially - the pilot must rely solely on the controller for collision avoidance protection. (That's changing, however. The introduction of traffic alert and collision avoidance systems � TCAS - and other similar cockpit-based devices give pilots an entirely new collision avoidance tool that they control.) But as soon as the airplane pops out of the murk into the clear, the pilot becomes responsible for visually scanning for other traffic and avoiding conflicts - see and avoid.
See and avoid is a bedrock principle in collision avoidance theory and practice, and probably � hopefully - will remain so until human pilots are permanently kicked out of the cockpit by know-it-all automated electronic control systems. Until then, in VFR conditions we pilots are responsible for keeping ourselves out of harm's way, regardless of any ATC traffic advisory services being provided.
When requesting VFR radar advisories, it helps to understand that the service is provided on a workload-permitting basis. If the controller is busy with other traffic, or ATC surveillance radar is inoperative, you'll probably get a polite "Unable." The reason for the denial may or may not be provided - the controller is under no obligation to explain.
If the controller agrees to your request, don't expect the same level of service as IFR aircraft. Controllers separate traffic according to a priority system, and IFR traffic has a higher priority than VFR traffic. The controller's primary responsibility is separating IFR aircraft from other IFR aircraft. Next is separating IFR from VFR. After attending to all of that, the controller may have time to devote to separating "participating" VFR aircraft (pilots who request and are granted radar advisory service, and who are issued a discrete Mode C transponder code) from other VFR aircraft.
Once a controller agrees to VFR traffic advisories, that controller is obligated to provide the service. In other words, the controller can't simply choose to ignore potential conflicts between participating VFR aircraft or fail to notify the affected pilots. The rub is the priority system discussed earlier. If the controller is busy separating a number of IFR aircraft, lower-priority VFR targets will have to wait their turn.
Separation is achieved by assigning aircraft to different altitudes; maintaining a minimum distance or time between aircraft on the same, converging, or crossing courses; and laterally by assigning different flight paths. The separation standards differ according to the airspace and distance from ATC radar antennae, and the type of radar equipment used. Generally, the minimum separation between two IFR aircraft is 1,000 feet vertically or three miles laterally. At higher altitudes, minimum separation may be 2,000 feet vertically or five miles laterally.
In Class B airspace, a controller has separation standards for VFR aircraft, but at greatly reduced minimums. Outside of Class B, however, there are no required separation minimums when a VFR aircraft is involved.
Separation can mean different things to different people. You may think you've just witnessed a near-collision when an unannounced airplane suddenly streaks by 500 feet under your nose, when in fact the controller was aware of the converging traffic. No conflict alert was issued because there was no real conflict. This may have been the case with the pilot who queried our tower chief.
VFR traffic advisories are a great tool to help us keep our distance from other airplanes, but it's not exactly something for nothing. The fact that an air traffic controller agrees to watch for conflicting traffic does not relieve us of the responsibility to do the same by visually scanning the skies as we fly.
Mark Twombly is a writer and editor who has been flying for 35 years. He is co-owner of a Piper Twin Comanche and recently obtained his commercial multiengine rating.
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