Airports referenced in this story
NextGen Implementation Plan Portfolio
Time Based Flow Management
- Enhances system efficiency and improves traffic flow by leveraging the capabilities of the Traffic Management Advisor decision-support tool, a system that is already deployed to all contiguous U.S. Air Route Traffic Control Centers.
Imagine that part of your daily commute was driving on a congested highway where three busy lanes of cars have to slow down to merge into one lane of traffic. Every day as you exited that highway and headed to your office you were not sure if you would be able to park in the parking lot when you arrived or if you would be asked to circle the parking lot until there was an available space.
This scenario, constant streams of aircraft heading for landing at a busy airport, is one that air traffic controllers at Air Route Traffic Control Centers have to manage around the clock. The key to reducing delays is increasing predictability.
The FAA has a NextGen automation tool in place that helps Center controllers do just that. Time-Based Flow Management, or TBFM, predicts what time all the flights will get to the point in the air where they start to make their descent to the airport about an hour before they get there. This key point in accurately predicting the arrival sits at the boundary between the Center's airspace and the airspace controlled by the Terminal Radar Approach Control (TRACON) facility. Of course, all aircraft can't arrive at this same spot at the same time, so the tool determines the most efficient schedule to get each flight to this spot. TBFM then builds a 4-dimensional (latitude, longitude, altitude and time) trajectory for each flight. That is, it decides the exact times the aircraft needs to be at certain intermediate points along the way in order to get to its scheduled time to begin to make its descent.
Controllers receive these scheduled times of arrival on their radar screens. They then guide the flights so that each aircraft reaches its intermediate points at the right time while maintaining the required separation between the aircraft. This is an activity known as time-based metering.
Say, for example, that TBFM predicts that three flights heading to Newark Liberty International Airport in New Jersey will all get to the airspace boundary between New York Center and New York TRACON at 11:00 a.m. TBFM determines that flight1 should still arrive at 11, but flight 2 should arrive at 11:05 a.m. and flight 3 at 11:10 a.m. The Center controllers then delay flights 2 and 3 by a few minutes, which they can do by assigning them a slower speed or a different altitude.
Time-based metering is more effective the more airspace controllers have available. When an airport is located close to its Center's airspace boundary, controllers don't have as much time or airspace to meet the scheduled times of arrival. So, the FAA extended the capability beyond a single Center's airspace, enabling controllers from adjacent Centers to meter aircraft bound for the arrival airport.
Adjacent Center Metering (ACM) increases the amount of airspace and time controllers can use to maneuver aircraft to meet their scheduled times of arrival and expands the benefits of time-based metering to aircraft that are farther away from the arrival airport.
This is the case for Newark. Because Newark is located close to New York Center's airspace boundary, controllers don't have enough airspace to achieve scheduled times of arrival. However, with ACM, introduced at Newark in 2008, controllers from New York, Boston, Cleveland and Washington centers now meter all aircraft bound to Newark in one synchronized, organized flow. And because of the traffic demands placed on Newark at some peak periods, controllers begin maneuvering aircraft to meet these scheduled times of arrival while the aircraft are still nearly 400 miles away.
Aircraft flying in high altitude airspace burn less fuel and there is less aircraft exhaust emissions, making this procedure good news for the airlines and the environment. A more predictable system means fewer delays and that is the good news for passengers everywhere.