"If we knew what we were doing, we wouldn't call it research, would we?" - Albert Einstein

Vicki Cox, senior vice president and supervisor of the FAA's NextGen program, likes to cite the iconic physicist's famous quote when discussing the challenges implicit in bringing her agency's ambitious ATC automation plan to reality.

Of course the FAA and its European counterparts, EASA and Eurocontrol, think they do know what they're doing, in terms of mapping how air traffic management can meet aviation's coming needs while accommodating the issues of energy conservation and environmental protection. Still, they, the aerospace industry and academia are also aware they have considerable work to do to create the new system. As Joel Klooster, FMS product development engineer at GE Aviation Systems, put it, "You don't know what you don't know until you actually try it."

The reason is obvious: NextGen and Single European Sky (known as SESAR) represent a new paradigm in separating aircraft and getting millions of passengers to their destinations in safety and - here's the caveat driving the proposed transformation - on time. The programs propose nothing short of actually automating ATC and conferring upon it a level of predictability hitherto unprecedented in the 80 years or so that public air transportation has existed as an industry. Consequently, major program goals include significant reduction to outright elimination of flight delays and the long-awaited liberation of operators from adherence to the airways system with consequent step changes in efficiency and fuel conservation.

In addition to new constraints related to noise and greenhouse gas (GHG) emissions, another major limitation to air traffic growth in North America and Europe over the next two decades will be terminal airspace and runway capacity. Those issues are addressed in the conceptual planning behind the new systems (see "SESAR: Europe's Impressive ATM Plan," June 2009). While the current financial downturn may temporarily slow the growth of all forms of air transport, the FAA and Eurocontrol have forecast a doubling of operations by the 2020s, which - if it occurs - would apparently overwhelm the contemporary ATC system.

Flying Ballistic Profiles

The solution air traffic management (ATM) solons in the U.S. and Europe have proposed for alleviating system congestion is "trajectory-based operations" (TBO) augmented by required time of arrival (RTA) at fixes throughout a flight and at destination. Thus, operations will evolve from estimated time of arrival to controlled time of arrival (CTA).

Together, these concepts constitute the basis for 4-D navigation - the fourth dimension being time -