The primary responsibility of air traffic controllers is the separation of aircraft. They control traffic in and around airports and in the terminal and enroute airspace in between. Controllers speak directly with pilots, notifying them of traffic or weather in their vicinity. Pilots depend on the instructions they receive from Air Traffic Control to safely and efficiently travel from their origins to their destinations.
In contrast, Traffic Managers facilitate a "system approach" to managing traffic that considers the impact of individual actions on the whole. Managing disruptions in airspace capacity (caused for example by bad weather, traffic overloads, or emergencies) requires consideration of who or what may be impacted by events, and a coordinated mitigation effort to ensure safety, efficiency and equity in the delivery of air traffic services. Without a coordinated response, local flight delays due to small disruptions can quickly ripple across the entire US, causing large scale rerouting, flight cancellations, and significant widespread delays. Traffic management in the National Airspace System (NAS) is overseen by the Air Traffic Control System Command Center (ATCSCC). Traffic management also takes place in the enroute Centers, in some of the large Terminals, and in collaboration with other stakeholders in the NAS, including the airlines, general aviation, and the military.
Tactical traffic management typically refers to the tasks or procedures that are carried out in a relatively short amount of time (< 2 hours) in a localized area. Strategic management, on the other hand, refers to a longer-range planning effort (2-8 hours) at a larger, perhaps regional or national scale.
The scale of convective weather impacts (typically thunderstorms) largely determines the severity and scope of traffic management initiatives that will be implemented, and their lead time.
As shown in the left side of the diagram above, moderate constraints that impact local areas of terminal or enroute airspace can be managed tactically, 0-2 hours prior to onset of convective weather. As a line of storms (labelled Weather) hits the Dallas/Ft. Worth TRACON (thin red octagon in center), the approaching aircraft, shown as blue dots with trailing blue lines, are placed in holding stacks (oval areas made up of several blue lines) until the weather clears the airport.
Significant regional weather constraints (middle image) must be managed strategically, 2-6 hours prior to the onset of convective weather. Pre-set boundaries called Flow Constrained Areas (FCAs; shown as thick blue lines), are used to control the demand through the weather impacted area. An Airspace Flow Program can be set to limit the traffic flow to a set number of aircraft per hour (shown as large grey arrows) across the FCA during the weather event (four large red ovals from Michigan to Pennsylvania, labelled Weather).
Large scale, intense convective weather (right image) can render airspace completely unusable. When this type of weather (large red oval stretching from New York to Tennessee labelled Weather) occurs, the full flow of aircraft scheduled for that airspace must be rerouted around the blockage. Large scale strategic traffic flow management requires lead times of 4-8 hours to modify the routing for large numbers of aircraft.
Today, the selection of strategic traffic management initiatives during convective weather events relies on experienced traffic flow managers interpreting evolving weather impacts, collaborating with NAS stakeholders, and planning traffic demand to fit within the available airspace. The challenges these managers face — hedging uncertainty in the weather impacts, preventing overload of enroute and terminal resources, and equitably allocating the limited resources among airlines — are especially frequent during the summer months, when the most thunderstorms (and the most air traffic delays) occur.
In general, strategic traffic flow management requires clear, high confidence predictions of weather impacts on airspace capacity 2-8 hours ahead of time. NextGen Weather provides a number of capabilities that support these operational needs, including 2-8 hour Predictive Products, Translation Products, and Confidence Metrics.