Ever since I can remember, when it comes to measuring the performance of the nation’s air transportation system, the aviation community has focused on safety, capacity, and delays. These have been the primary yardsticks of performance.  The legislation that created the FAA cites safety and efficiency as its primary mission, but efficiency is difficult to measure, so efficiency was translated into capacity. It turns out that capacity is hard to deal with as well, so delays became the surrogate for efficiency and capacity. Even important parameters like fuel, crew and equipment costs largely were measured based on impacts due to delays.

In the mid-1990s, FAA’s Western-Pacific Regional Administrator Carl Schellenberg came to FAA Headquarters. Carl assumed responsibility for the Airport Capacity Office, whose mission in life was to increase airport capacity – figure out where it was needed or going to be needed, and then work with the right people and do whatever had to be done to build it. Carl was a lawyer by training and had acquired a wide range of critical skills that made him the right person for that job. When you study the system from this perspective, you come to recognize that airports are just one component of a complex system. It’s not just concrete and terminal buildings, but airspace, air traffic management services, airlines, passengers, environmentalists, and the local economy that relies on and supports aviation. Shortly after getting settled in his job, he began to question the adequacy of existing performance measures. He said that safety and efficiency/capacity/delay were important, but not enough. He began promoting predictability, flexibility and access as additional measures and goals to strive for. While these ideas resonated with many, very little progress was made to quantify them. So, after a while they faded from discussion, with safety and efficiency/capacity/delays continuing to serve as the main institutional measures of system performance.

It had been over ten years since I had focused on predictability, flexibility and access. A lot has happened since Carl first introduced them. I’ve come to realize that I have seen examples over the years that may allow us to begin quantifying these elusive measures. It could very well turn out that these measures are associated with large pools of economic benefits that ought to influence the design of NextGen policies, concepts and technologies.

Last year we were doing human-in-the-loop simulations with airline dispatchers interacting with the FAA in rerouting major traffic flows around large, convective weather systems. We wanted to see how well the airlines were able to cope with large numbers of rerouted flights. We anticipated that reroutes would be designed to keep the flight path as short as possible to save fuel and time. Instead, we saw instances where the airlines were selecting reroutes with bigger deviations that resulted in longer and seemingly more costly flight paths. On further inquiry, we learned that these flights were rerouted on a longer path because it was more important to have a predictable arrival time, since the destination runway, gate, ground crews and equipment were in short supply. In other words, the airlines were flying further, burning more fuel and taking more time to be more assured of arriving when planned, so that all of the resources needed were available when needed. When we begin to think about the system more as a supply chain system with a myriad of interdependent pieces, taking a longer and seemingly less efficient reroute begins to actually make sense. The overall costs in the end are lower.    How much is predictability worth? We begin to get some sense of its worth when we add up all of the fuel, crew and equipment time spent to reduce the uncertainty in arrival times.

Flexibility is provided to some degree today. During schedule disruptions, working through the FAA’s collaborative decision-making processes, the airlines have the ability to swap their flight positions in a flight schedule. They can decide to take delays on the ground at the origin airport or leave earlier and risk taking delays in the air, where they’re more costly. These decisions enable them to better achieve their individual business objectives, which include passenger satisfaction, utilization and cost of the many different types of resources needed to support a flight, and impact to the overall network schedule. In the next couple of years, they will be able to request multiple flight trajectory options together with the valuation of each option and the conditions under which they apply. The FAA will use this information in automated processes to more dynamically respond to changing capacity conditions. In the end, the airlines will get more of what they want and the FAA will make the most of limited, dynamic airspace resources. In the longer term, flight planning will build more flexibility into flight plans. The increased flexibility in flight plans will allow them to better deal with uncertainties in weather, traffic congestion, and other phenomena. Each of these forms of flexibility enables the airlines to better meet their business objectives and is worth a lot.

On the issue of access, I’m going to look at access from the perspective of communities. Hub and spoke networks have inherent strengths. The greatest of these is their ability to serve so many origin-destination pairs. One schedule bank containing n aircraft in a hub and spoke network can theoretically serve up to n(n-1)city pairs. A typical bank might include 30 aircraft, so for n=30, n(n-1) is 870 city pairs. One downside of the hub and spoke is that to maximize connectivity and efficiency, you have to maximize the flights in a bank and minimize the time it takes to land the bank, unload, service, reload and depart. To work well from an airline perspective, you want the demand pattern to be as peaky as possible. From air navigation service provider and airport operator perspectives, peaky is very bad, since it drives the sizing and cost of your infrastructure and staffing. It’s like feast or famine, so the infrastructure and staff often suffer peaks and valleys and inefficiencies in utilization. Another disadvantage of hub and spoke is that it’s fragile. A few flights get out of sync and things unravel in a hurry. As a result of criticism and problems, the airlines have reduced over-scheduling and de-peaked. As these reductions have occurred, consider what happens when you go from 30 to 20 aircraft in a bank. For n=20, n(n-1)=380, which means 10 fewer aircraft in a bank and up to 490 fewer city pairs served. Many smaller communities fall off, either losing more frequent service or losing scheduled air service all together. What are the regional and aggregated national losses associated with that?

I think Carl was right. It’s time to take a harder look at the economic value associated with predictability, flexibility and access. NextGen needs to support performance in these terms in addition to safety and delays. Have we been ignoring the need for these potential high-value outcomes? We very well may be sitting on top of sizable, untapped pools of benefits. Focusing on predictability, flexibility and access could make NextGen all the more robust and valuable.