January 31, 1996 Tower BRITEs |
|
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.
January 31, 1996
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.
Basic Rules
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.
Highly Variable
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.
|
Email this article
