These days, more and more towers have radar but that doesn't necessarily mean they can provide the same separation services as approach and Center. A veteran controller from O'Hare tower gives the inside dope on the BRITE displays that towers use.
Ever notice how some towers seem to be more specific than others when it comes to pointing out traffic? At some airports, you can check in with the tower and instantly be told "...traffic is a Lear Jet just off the airport, southeastbound." That's the last you'll hear about the Lear until he fills your windshield. Yet, at other locations, the same scenario will net not only the initial traffic advisory but updated information on both the location and altitude of the traffic and even a reassuring "traffic no factor" when appropriate.
So what gives? The difference is due primarily to the equipment controllers have to work with. In the first example, the controller has a headset, a radio and (maybe) a pair of binoculars. In the second scenario, the controller has all that stuff, plus a secret weapon: a BRITE.
BRITE is FAA-speak for radar in the tower. The acronym means Bright Radar Indicator Tower Equipment and the system has real benefits for both pilots and controllers.
Good Views, But...
Towers have terrific views but the only thing more abundant in the cab than bad coffee and wisecracks is light. Since the display of a normal radar scope needs semi-darkness to be visible, the idea of just sticking a radar scope in the tower doesn't cut it. Enter television. No, I'm not saying we watch television in the tower. We tried it, but it distracted us from the card games. It's the technology of television I'm referring to.
As any self-respecting couch potato knows, television doesn't require a dark room so the original BRITE scopes, which came into service in the early 70's, work just like television. Somebody took one of the cumbersome video cameras of that era and stuck it in front of a radar scope. The image was then piped to a TVtype screen in the tower. Bingo, a radar display that could be seen in daylight. The BRITE idea was so successful that the FAA went for it full tilt, installing the new systems not just in towers but even in some tracons. Imagine the horror when the lights went on in control rooms that had been cleaned in the dark for the last 20 years.
The invention of BRITE was of sufficient magnitude to launch a new type of air traffic facility as well: the tracab, which is a radar approach control facility located in the tower cab of the primary airport, as opposed to a separate room in the basement.
Many tracabs have since reverted to tracons, since the tower folks have enough problems keeping track of what's happening outside the windows without having to circumnavigate a radar facility on their way from one side of the tower to the other.
What It Does
Okay, so what's all this got to do with you, as you motor along through the ATC system? There are some important distinctions regarding BRITEs and their use that pilots should be aware of. First, the pilot has absolutely no way of knowing which towers have a BRITE. The feds say that the various radar uses are strictly a function of FAA operational need, so there's no publication that tells which facilities are BRITE equipped.
In the many facilities that have no BRITE, the controllers use strictly visual means to find and sequence traffic. Towers that do have BRITEs may have one of several different types. Some have only a very crude display which gives a fuzzy picture of blips on a field of green, perhaps with the capability of displaying an extra slash on transponderequipped targets and a larger slash when a pilot hits the ident button. Next in sophistication are BRITEs that have alphanumeric displays of various types, ranging from transponder codes and altitude to the newest Buck Rogers version, the DBRITE.
The D stands for digital, meaning that a computer takes all the data from the primary radar, the secondary radar (transponder information), and the computer that generates the alphanumeric data. It's digitizes the image then sends it all, in TV format, to a display in the tower. The new displays are square and provide an excellent presentation, regardless of how bright the ambient light.
To understand what kind of service you might receive from a tower with a BRITE, you have to know the basic methodology when it comes to Letters of Agreement (LOAs) and delegated airspace. In the beginning, all airspace is "owned" by the Centers.
The Centers, in turn, sign LOAs with various approach control facilities, delegating those facilities chunks of airspace in which that approach control facility has jurisdiction. The approach control facilities, in turn, sign LOAs with various towers that are within that airspace, further delegating airspace and responsibility.
Some facilities, called "Limited Radar Approach Control Towers" are granted full separation responsibilities within their small (usually 5-mile radius or less) delegated airspace. These controllers use their BRITEs in much the same way tracon controllers would, providing the kind of radar service you're used to, using the same techniques.
But, while any facility with a BRITE can use the device as an extra set of eyes to assist sequencing, the majority of BRITE equipped towers operate with restrictions on the use of the BRITE for separation of IFR traffic. Many have constraints on how the BRITE can be used when dealing with VFR traffic as well.
Some of the limitations are imposed by LOAs. For instance, at Chicago's Dupage airport, the LOA with Chicago approach (which "owns" the airspace, having been delegated responsibility for it from Chicago Center) allows the Dupage tower controllers to use the radar only to provide initial departure separation between successive IFR departures, but not between an arrival and a departure, or between two arrivals. Consequently, an IFR departure may be held on the ground due to the presence of an IFR arrival, even though the controller knows exactly where the arrival is and that the release of the departure wouldn't be a factor.
However, the most limiting factor in the use of the BRITE is not found in the LOAs but in the basic idea behind the use of radar in the tower. The radar service provided by a tower controller is not, nor was it ever intended to be, the same thing as radar service provided by an approach control or Center.
It can't be. The primary duty of tower controllers is to separate airplanes operating on the runways, which means the controller spends most of his time looking out the window, not staring at a radar scope. It's roughly analogous to a pilot flying instruments in clear VMC. He or she really needs to be looking outside the cockpit most of the time, not at the instruments.
What the AIM Says
The AIM explains all this (section 4-52d), in general terms. To summarize, controllers are allowed to use BRITEs for four tasks: to determine an aircraft's position, provide traffic advisories, offer suggested headings and to provide general information.
In furnishing these services, controllers may use any of the normal radar identification methods (transponder idents) to find out where you are. But once they've done so, they might not look at your target again. So don't think you're going to get the same type radar service from the tower controller as you would from a guy that has nothing else to do but watch the sweep going around. Also, remember that traffic advisories are workload permitting; some days you'll get complete advisories, some days not.
Note that there's a difference between a BRITE-provided "suggested heading" and a vector. In fact, the directional guidance provided to VFR aircraft by most tower controllers is specifically not a radar vector but a generalized instruction, i.e. "proceed southwestbound." The AIM explains that pilots have discretion regarding acceptance of such guidance and they remain solely responsible for seeing and avoiding other aircraft.
Because of this cafeteria criteria for radar service by tower controllers, you'll rarely hear the words "radar contact" from them and this is an important distinction. It's only when an airplane is officially in "radar contact" that the full menu of radar service is being provided.
That's why the AIM is so specific in informing pilots of what really happens when radar service is terminated, even in cirumstances when the tower has a BRITE in the cab and can see airplanes nearly down to the surface.
The authors of the AIM are quite emphatic on this point, since it appears in all caps at the end of paragraph 4-52d: "WHEN IN COMMUNICATION WITH A TOWER CONTROLLER WHO MAY HAVE RADAR AVAILABLE, DO NOT ASSUME THAT CONSTANT RADAR MONITORING AND COMPLETE ATC RADAR SERVICES ARE BEING PROVIDED."
From where I sit in the tower, that's pretty good advice.