Ever notice how some towers seem to be more specific than otherswhen it comes to pointing out traffic? At some airports, you cancheck in with the tower and instantly be told "…trafficis a Lear Jet just off the airport, southeastbound." That’sthe last you’ll hear about the Lear until he fills your windshield.Yet, at other locations, the same scenario will net not only theinitial traffic advisory but updated information on both the locationand altitude of the traffic and even a reassuring "trafficno factor" when appropriate.
So what gives? The difference is due primarily to the equipmentcontrollers have to work with. In the first example, the controllerhas a headset, a radio and (maybe) a pair of binoculars. In thesecond scenario, the controller has all that stuff, plus a secretweapon: a BRITE.
BRITE is FAA-speak for radar in the tower. The acronym means BrightRadar Indicator Tower Equipment and the system has real benefitsfor both pilots and controllers.
Good Views, But…
Towers have terrific views but the only thing more abundant inthe cab than bad coffee and wisecracks is light. Since the displayof a normal radar scope needs semi-darkness to be visible, theidea of just sticking a radar scope in the tower doesn’t cut it.Enter television. No, I’m not saying we watch television in thetower. 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’trequire a dark room so the original BRITE scopes, which came intoservice in the early 70’s, work just like television. Somebodytook one of the cumbersome video cameras of that era and stuckit in front of a radar scope. The image was then piped to a TVtypescreen in the tower. Bingo, a radar display that could be seenin daylight. The BRITE idea was so successful that the FAA wentfor it full tilt, installing the new systems not just in towersbut even in some tracons. Imagine the horror when the lights wenton in control rooms that had been cleaned in the dark for thelast 20 years.
The invention of BRITE was of sufficient magnitude to launch anew type of air traffic facility as well: the tracab, which isa radar approach control facility located in the tower cab ofthe primary airport, as opposed to a separate room in the basement.
Many tracabs have since reverted to tracons, since the tower folkshave enough problems keeping track of what’s happening outsidethe windows without having to circumnavigate a radar facilityon 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 alongthrough the ATC system? There are some important distinctionsregarding BRITEs and their use that pilots should be aware of.First, the pilot has absolutely no way of knowing which towershave a BRITE. The feds say that the various radar uses are strictlya function of FAA operational need, so there’s no publicationthat tells which facilities are BRITE equipped.
In the many facilities that have no BRITE, the controllers usestrictly visual means to find and sequence traffic.Towers that do have BRITEs may have one of severaldifferent types. Some have only a very crude display which givesa fuzzy picture of blips on a field of green, perhaps with thecapability of displaying an extra slash on transponderequippedtargets and a larger slash when a pilot hits the ident button.Next in sophistication are BRITEs that have alphanumeric displaysof various types, ranging from transponder codes and altitudeto the newest Buck Rogers version, the DBRITE.
The D stands for digital, meaning that a computer takes all thedata from the primary radar, the secondary radar (transponderinformation), and the computer that generates the alphanumericdata. It’s digitizes the image then sends it all, in TV format,to a display in the tower. The new displays are square and providean excellent presentation, regardless of how bright the ambientlight.
To understand what kind of service you might receive from a towerwith a BRITE, you have to know the basic methodology when it comesto Letters of Agreement (LOAs) and delegated airspace. In thebeginning, all airspace is "owned" by the Centers.
The Centers, in turn, sign LOAs with various approach controlfacilities, delegating those facilities chunks of airspace inwhich that approach control facility has jurisdiction. The approachcontrol facilities, in turn, sign LOAs with various towers thatare 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 controllersuse their BRITEs in much the same way tracon controllers would,providing the kind of radar service you’re used to, using thesame techniques.
But, while any facility with a BRITE can use the device as anextra set of eyes to assist sequencing, the majority of BRITEequipped towersoperate with restrictions on the use of the BRITE for separationof IFR traffic. Many have constraints on how the BRITE can beused when dealing with VFR traffic as well.
Some of the limitations are imposed by LOAs. For instance, atChicago’s Dupage airport, the LOA with Chicago approach (which"owns" the airspace, having been delegated responsibilityfor it from Chicago Center) allows the Dupage tower controllersto use the radar only to provide initial departure separationbetween successive IFR departures, but not between an arrivaland a departure, or between two arrivals. Consequently, an IFRdeparture may be held on the ground due to the presence of anIFR arrival, even though the controller knows exactly where thearrival is and that the release of the departure wouldn’t be afactor.
However, the most limiting factor in the use of the BRITE is notfound in the LOAs but in the basic idea behind the use of radarin the tower. The radar service provided by a tower controlleris not, nor was it ever intended to be, the same thing as radarservice provided by an approach control or Center.
It can’t be. The primary duty of tower controllers is to separateairplanes operating on the runways, which means the controllerspends most of his time looking out the window, not staring ata radar scope. It’s roughly analogous to a pilot flying instrumentsin clear VMC. He or she really needs to be looking outside thecockpit most of the time, not at the instruments.
What the AIM Says
The AIM explains all this (section 4-52d), in general terms. Tosummarize, 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 normalradar identification methods (transponder idents) to find outwhere you are. But once they’ve done so, they might not look atyour target again. So don’t think you’re going to get the sametype radar service from the tower controller as you would froma 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 "suggestedheading" and a vector. In fact, the directional guidanceprovided to VFR aircraft by most tower controllers is specificallynot a radar vector but a generalized instruction, i.e. "proceedsouthwestbound." The AIM explains that pilots have discretionregarding acceptance of such guidance and they remain solely responsiblefor seeing and avoiding other aircraft.
Because of this cafeteria criteria for radar service by towercontrollers, you’ll rarely hear the words "radar contact"from them and this is an important distinction. It’s only whenan airplane is officially in "radar contact" that thefull menu of radar service is being provided.
That’s why the AIM is so specific in informing pilots of whatreally happens when radar service is terminated, even in cirumstanceswhen the tower has a BRITE in the cab and can see airplanes nearlydown to the surface.
The authors of the AIM are quite emphatic on this point, sinceit appears in all caps at the end of paragraph 4-52d: "WHENIN COMMUNICATION WITH A TOWER CONTROLLER WHO MAY HAVE RADAR AVAILABLE,DO NOT ASSUME THAT CONSTANT RADAR MONITORING AND COMPLETE ATCRADAR SERVICES ARE BEING PROVIDED."
From where I sit in the tower, that’s pretty good advice.