Introduction
The visible RESOURCES of the NAS-the nation's airspace, its airports
with their runways, taxiways, and gates-are what the flying customer feels.
When the NAS resources are strained, then the customer feels delays or
cancellations. It is the activity on the NAS resources that can be most
readily measured and understood. Thunderstorms that diminish or extinguish
the throughput of an airport, say, can be measured and the effects of
the phenomenon measured.
More aircraft are flying now than ever before. Costs of tickets and commodity
delivery are contained at a price reachable by most of the population
thanks to the expansion of the economy during the 1990s. The air transportation
system in the U.S. is the safest in the world, much safer than transportation
by automobile. The benefits of rapid and safe transportation keep pushing
the traffic numbers higher. NAS resources are straining under the burden
of this rapidly evolving air commerce.
Like most transportation systems, there is a limit to growth. We are
beginning to see this limit in the system's increasing delays and cancellations.
Local phenomena have global consequences. To make matters worse, it takes
a lot of time to effect change. For example, to expand airport capacity
by building new runways generally takes years to get proposals through
the environmental impact process (and allay local fears) to the stage
where construction can start. Reformulation of the nation's airspace (how
it's structured, how people use it) is likewise a difficult job. Paramount
in this is the ability to analyze the problems and identify root causes,
identify potential solutions backed up by analysis.
Metrics
Among engineers, it is taken as a matter of principle that if you can't measure it, you'll never be able to improve it. How true this is with the U. S. Aviation System. For too long, measurements focused mainly on delays, but in measuring just delays we'll never get to the roots of the system's problems. What causes delays? Measure and then attack the root causes of delays, then you have something to build on.
CAASD has been working with the FAA and within the aviation community to identify new metrics with which to gauge the performance of the nation's aviation system, and to develop the processes that capture the necessary data to measure how well the NAS is performing.
Besides delay, CAASD has identified metrics such as flexibility and access to measure how well the NAS responds to user preferences. All these measures are produced on a daily basis in a report card format for FAA senior managers.
The NAS Report Card produces information most pertinent to domestic air commerce. CAASD has developed other metrics to measure the performance of the NAS for oceanic airspace users. Because of the structure of oceanic airspace and the oceanic route system, a different set of metrics was necessary to understand the performance of this segment.
The capture and collection of data, and the subsequent processing to obtain usable information is important; if you can measure it but not on a continuous basis, then you haven't helped. CAASD's Oceanic Analysis Tool Set is an example of the kind of work we do to capture and analyze parameters that describe how the NAS performs.
Airspace
The nation's airspace is a NAS resource. The airspace has got a structure—an architecture—to it. A sector of en route airspace (a three-dimensional volume of airspace) is controlled by a sector team. The sector is assigned a set of frequencies to use in controller communications with aircraft passing through the sector. The size and the shape of a sector is determined by the underlying navigation, the prevailing flows of traffic in the area, and the need to keep the number of aircraft simultaneously in the sector below a given threshold. The introduction of new technology is also a factor pushing for change in how the airspace is designed.
CAASD has been very active in the  National Airspace Redesign effort undertaken by the FAA. Using computer simulations and analytical models, CAASD is working to effect changes in the architecture of the airspace to be better able to accommodate all the traffic as the traffic volume increases and the capabilities of aircraft (especially with respect to navigation) continue to evolve. Analyses of the airspace (how it is used, the prevailing traffic flows, etc.) show that improvements can be made to increase the efficiency of traffic flows.
Even bigger than the airspace around the airports, the National Airspace Redesign is looking at what keeps the nation's airspace from safely accommodating more traffic. CAASD is working with FAA Headquarters and the different Regions in proposing new structures to handle the expected growth.
On the local scale, CAASD is helping the FAA local facilities streamline operations  with anlyses and new airspace architectures. For example, CAASD assessed the impace of new arrival procedures on terminal airspace and ground operations in Atlanta. Basically, each airport is different in the way its sits with respect to geography, proximity to urban polulations, and the NAS navigation systems and surrounding airways, etc. CAASD has identified the different choke points of the NAS and is working to streamline traffic flows to enhance capacity.
Airport, Runways, and Gates NAS resources include not only the nation's airspace, but also such things as the airports, runways, taxiways, gates, etc. NAS resources have a certain capacity; when the demand for a NAS resource exceeds the capacity of that resource, then it is necessary for an allocation—hopefully equitable—of the available capacity to the demand. This will generally require slowing the arrival of aircraft, rerouting of aircraft, holding of aircraft, etc., long enough for congestion to clear. To use the ground example, a policeman directing traffic after a Big Game will allocate the capacity of an exit roadway by blending the traffic from several exit streams onto the roadway in an organized way, balancing the demand to the capacity of the roadway to avoid gridlock. Just as an accident at rush hour rapidly backs up automobiles, so, too,  do local problems in the NAS affect large number of related—and even unrelated—aircraft.
Weather is the greatest source of delays and cancellations in the NAS.  However, if a weather system is well-behaved (in the sense that the path, strength, and extent of the system was predicted accurately well before the system affected traffic), then the effects of the weather can be mitigated. If the weather system evolved differently from how it may have been predicted, then the result can affect large populations of aircraft.
Resources Solutions
The key to solving the delays problem here in the U.S., and abroad, and moving the system towards Free Flight, is to create more capacity. Creating capacity allows the system to accommodate the demand from current and potential users of the nation's airspace, and comes in many forms. We think of the nation's airspace and airports reaching capacity meaning we have to find more airspace or build more airports and runways (a long and expensive proposition), but finding more capacity is more than airspace and runways. It's also the frequencies controllers and pilots use to communicate—they're jammed, in some places affecting throughput. It's the computers and the software running in them—new capabilities could help controllers and pilots better use the available capacity by safely tightening allowable separation distances. It's the airspace itself, and how it is broken into pieces small enough for controllers to handle the traffic (number of airplanes and the prevailing traffic structure have been key to sector design). It's arrival and departure routes, and the tracks given to the major traffic flows across the country. It’s the capabilities of aircraft to execute controller instructions. In short, it's everything. What makes the aviation system unique is this very interdependence of problems and of solutions. By themselves, individual problems seem not to make a difference, but they propagate into big problems affecting seemingly unrelated aircraft. Likewise, by themselves, single solutions can help solve local problems, but it is all the solutions acting in concert that will lead to needed capacity enhancement.
To understand the needs of the NAS, one must understand what motivates the users of the NAS. Clearly, the airlines are out to sell a product (their schedules) and make a profit. In so doing, they evolve their fleets with new capabilities to ensure they remain competitive. CAASD has been working with the airlines to better understand their business as part of documenting their needs.
One of the trends we are seeing in the evolution of how the airlines conduct their business is in the use of regional jets (RJs). RJs are small passenger carriers  with a capacity of around 70 searts. The airlines are using RJs more and more to service small communities. The RJ market is the fastest growing in the aviation industry. How they integrate with the larger jets is, however, a challenge. They fly high, but slower than traditional jet aircraft. CAASD has been tracking these trends and working the details so that these aircraft fit seamlessly with other users of the national airspace.
CAASD's simulations of airport operations provide  an ability to design and evaluate new airspace architectures designed especially to segregate aircraft with differing capabilities. This can increase throughput of airports by allowing aircraft to access alternate entry routes to, or exit routes from, airports, thus keeping the traffic going when the traditional "merge lanes" are full.
The study of the airspace user is a necessary, but not sufficient, activity to gauge the needs of the NAS. CAASD's analyses point out the interconnectivities of traffic streams, and the capacity of the nation's airports. CAASD looked at the nation's 31 busiest airports, determined their maximum capacities in good weather and in poor. What we found was that many of the nation's busiest runways are oversubscribed by the airlines. This, in turn, underscores the need for a coordinated effort to achieve maximum throughput of the NAS resources. Finally, CAASD analyses also took a look at the planned enhancements (new runways, etc.) to the NAS resources. It found that it will be necessary to redouble our efforts in the enhancement of the nation's resources if we are going to slow the growth of delays. Given the lead time necessary for the planning and building of new runways, it is likely that delays will continue to grow; other efforts to use as much of the available capacity as possible to increase the throughput of the airports will help. It will take the whole community to avoid gridlock in the NAS.
The FAA and CAASD have produced a plan for the operational evolution of the NAS and the creation of more capacity in the NAS to handle the growing demand for NAS resources. The problems are vast and the solutions numerous and complicated by the fact that solutions take on different characteristics in whatever geographic location they are implemented. (This is because the relationship of an airport to its surrounding environment, and the subsequent traffic characteristics inbound to and outbound from that airport, are different at each airport.)
CAASD is engaged on the local and national  levels in the debates necessary to move the evolution of NAS resources forward. We perform the modeling that backs up environmental impact statements and the Operational Evolution Plan. We've participated in the analyses that identify the tradeoffs on site selection for new airports. We've analyzed the traffic flow and airspace impacts of adding new runways. Entering the debate with believable analyses, debate times are then shortened
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