Continuing Ed

What ATC Can And Cannot Do With Radar

What kind of airport do you prefer, towered or nontowered? (Before answering, let's agree to avoid the use of the term uncontrolled, for nontowered. It's too easy for nonpilots to hear the word uncontrolled as meaning "out of control," which is far from the truth.) Fans of nontowered airports cite freedom of movement and efficiency - no waiting for taxi and takeoff clearances from a controller - as attributes, while towered-airport advocates appreciate the perceived safety of positive control of all traffic. After all, what could be safer than supplementing your eyes with positive air traffic control to make sure you don't come in conflict with any other aircraft in the terminal area?

Safety is every responsible aviator's first concern, and the pilot is primarily responsible for collision avoidance. Even pilots flying under instrument flight rules (IFR), when they aren't inside clouds, are charged by the regulations with the responsibility of looking out for other aircraft. But if you think that safety is enhanced in terminal areas because tower controllers "separate" aircraft - maintain minimum lateral and/or vertical distances between aircraft in the terminal area for collision avoidance purposes - think again.

The basic function of an airport air traffic control tower is, in the FAA's own words, to provide for a "safe, orderly, and expeditious flow of traffic on and in the vicinity of an airport." That means tower controllers are responsible primarily for sequencing traffic, both departing and arriving, to avoid conflicts on the runways. That's different than the lateral and vertical separation of aircraft in the air that approach and air route traffic control center controllers achieve with the use of radar. It's important to be aware of the distinction so that your expectations of the services you receive from a tower controller don't exceed reality.

Airport control towers differ from other air traffic control facilities - en route centers and terminal radar approach controls (tracons, commonly addressed on the radio as approach and departure control) - in that tower controllers rely primarily on their eyes to separate aircraft. Tracon and center controllers, on the other hand, use radar exclusively to control aircraft movements and prevent collisions.

It's easy to develop the mistaken notion that airport control towers provide the same level of separation service as tracons and en route centers, especially if you make a habit of asking for VFR traffic advisories or flight following whenever you venture out of the terminal area on a VFR flight.

For example, if I'm returning to Page Field in Fort Myers, Florida, after visiting my son in Gainesville in the northern part of the state, I'll request radar advisories on the flight home provided the weather is VFR. Over the course of the 90-minute flight I'll talk to Gainesville Tower, Jacksonville Approach, Jackson-ville Center, Tampa Approach, Miami Center, Fort Myers Approach, and, finally, Page Tower.

A Gainesville Tower controller issues a transponder squawk code that will serve me until I land. Soon after taking off from Gainesville I'm told to switch to Jacksonville Approach. The Jacksonville controller answers my initial call with the acknowledgement "radar contact." That means I exist on the controller's radar scope, and I can be monitored and advised for collision avoidance purposes.

This process repeats itself as I fly south into Tampa, Miami, and Fort Myers airspace. After listening to the Page Field ATIS and spotting the airport in the distance, I report to Fort Myers Approach Control that I have the field in sight. "Roger, radar service terminated, contact Page Tower." The tower acknowledges my initial call and issues landing instructions. It's been a good, safe trip, in part because I've been protected by the watchful electronic eyes of ATC from takeoff to touchdown.

Well, not exactly. The phrase "radar service terminated" issued by the Fort Myers approach controller should be my tip-off that the radar-based traffic advisories I've been enjoying throughout the flight are over and done with. Sure enough, when my call to the tower was acknowledged, I did not hear those magic words "radar contact," even though I know from my visits to the tower cab that the controllers have access to a radar depiction of area air traffic.

The tower radar display is known as BRITE, an acronym for bright radar indicator tower equipment. Basically, it is a television image of the radar display in the Fort Myers Approach Control radar room some six miles to the southeast at Southwest Florida International Airport. Television technology is used for the tower cab radar display because a conventional radar screen could not be seen well in the sun-filled daytime environment of a tower cab.

So, our tower controllers - along with many other air traffic control towers across the country - do have access to a radar depiction that shows the location of all aircraft in the area. If that's the case, why don't they use it to issue precise traffic advisories in the same way that approach and center controllers do?

The simple reason is that most tower controllers are not certified by the FAA to use the radar display for such purposes. The only tower controllers permitted to do so are those who work at larger airline airports with a combined ATC approach control and tower complex, and who rotate between tower duty and working the scopes in the approach control radar room. At smaller airports with a control tower but no approach control facility, controllers can use the BRITE display only as a supplement to their eyes.

That's why when you are inbound to a tower-controlled airport, you aren't likely to hear the tower controller respond to your initial radio call with the words "radar contact." When flying into or out of a tower-controlled airport, don't assume you are being watched on radar, even though the tower may be equipped with a BRITE radar display. In the FAA's own language, "...uncertified displays shall be used only as an aid to assist controllers in visually locating aircraft or in determining their spatial relationship to known geographical points."

The fact is, when it comes to spotting traffic in the terminal area, tower controllers must rely primarily on their Mark I eyeballs - and so should you. Give precise position reports to the tower, and keep your head up and scanning.

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.