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much as an hour before the aircraft arrives at the TRA-
CON. It can potentially increase operational capacity by
up to ten percent, and has improved capacity by 3 to 5
percent for traffic into the Dallas/Ft. Worth, Los
Angeles, Minneapolis, Denver, and Atlanta airports.
One limitation of TMA is that it uses information on
incoming flights from a single Air Route Traffic Control
Center (ARTCC). Another version is under development
that will integrate information from more than one
ARTCC. It is called multi-center traffic management
advisor (McTMA). This system is being tested in the
busy Northeastern area, and the results are promising.
Another software-based solution is the passive final
approach spacing tool (pFAST). This software analyzes
the arriving traffic at a TRACON and suggests appropriate runway assignment and landing sequence numbers
to the controller. Controllers can accept or reject the
advisories using their keyboards. The early version carries the “passive” designation because it provides only
runway and sequence number advisories. A more
advanced version, called active FAST (aFAST), is currently under development at NASA Ames Research
Center. In addition to the information provided by
pFAST, aFAST will display heading and speed, and it is
expected to improve capacity by an additional 10 percent over pFAST.
Airlines can help ease congestion on shorter routes by
filing for lower altitudes. Although the airplane uses
more fuel at a lower cruising altitude, the flight may
prove faster and more economical if weather or high
traffic volume is delaying flights at higher levels. The
tactical altitude assignment program consists of published routes from hubs to airports 200 to 400 NM away.
Based on results of evaluation, it is not expected to be
implemented nationally, although it may remain available in local areas.
6-6
Beyond using existing facilities and procedures more
effectively, capacity can often be increased by making
relatively minor changes in air traffic procedures. For
example, in some instances, departure and arrival patterns have remained unchanged from when there was
very little air traffic, and congestion results when today’s
traffic tries to use them. Likewise, arrival and departure
procedures may overlap, either because they were based
on lower volumes and staffing or because they are based
on ground-based navigation. The interdependence of
arrival and departure routes tends to limit throughput in
both directions.
Separating departures from incoming traffic can simplify
the work of controllers, reduce vectoring, and make more
efficient use of terminal airspace. In the four corner post
configuration, four NAVAIDs form the four corners of
the TRACON area, roughly 60 NM from the primary airport. All arrivals to the area fly over one of these “corner
posts” (also called arrival meters or feeder fixes). The
outbound departure streams are spaced between the
arrival streams. [Figure 6-6]
As more and more aircraft are equipped for RNAV,
new arrival and departure routes are being created that
do not depend on very high frequency omni-directional range (VOR) airways or ground-based
NAVAIDs. Shifting traffic to new RNAV routes eases
congestion on existing airways. There are already several new RNAV routes in use and many more are being
developed.
SEPARATION STANDARDS
Current regulations permit a 3 NM separation within 40
NM of a single radar sensor. The FAA is looking at
ways to increase the use of the 3 NM separation standard to improve efficiency and maximize the volume
of traffic that can be safely moved into busy terminal
areas. The methods involve increasing the size of terminal areas to include more en route airspace,
redesigning airspace to encompass multiple airports
within a single ATC facility, and consolidating certain
TRACON facilities. This will involve major changes
on the ground for ATC facilities, and changes in
charts and procedures for pilots.
Figure 6-6. Four Corner Post Configuration.
6-7
As gaps are filled in arrival and departure streams and the
3 NM separation standard is applied more extensively,
traffic advisories from the traffic alert and collision avoidance system (TCAS) are bound to increase. While newer
software enhances functionality, provides more timely
resolution advisories, and eliminates many nuisance
alerts, data link technology based on GPS position information may offer even better results.
MAINTAINING RUNWAY USE
IN REDUCED VISIBILITY
Although traffic in congested airspace typically operates
under instrument flight rules (IFR), adverse weather and
　
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