Time Based Flow Management (TBFM) is a capability used to manage traffic flows by metering, or sequencing aircraft to their arrival airports. Through TBFM, an automation system uses a schedule of runway assignments and landing times to sequence inbound flights, and allocates delays to various segments of each flight in order to meet the assigned schedule. TBFM is administered by traffic managers at the Air Route Traffic Control Center (ARTCC) or Terminal Radar Approach Control facility of the arrival airport. For some airports, TBFM is used routinely, while at others it is used as needed.

TBFM provides four time-based metering functions:

• Arrival management/situational awareness to inform traffic managers of projected arrival demand
• Airborne metering to sequence flights and provide controllers with allocated delay assignments for each flight to meet the proposed schedule
• Departure scheduling to provide increased management of arrival demand by assigning delays to flights at their origin airports to help them merge into the arrival stream
• En route departure capability (EDC) to efficiently integrate departures into overhead en route streams

TBFM enables the more efficient use of available capacity by tailoring the allocation of delays to individual flights, thereby reducing the need for less efficient "one-size-fits-all" techniques such as Miles-in-Trail (MIT) restrictions. In turn, this can reduce total aircraft delays, and transfer delays to more fuel-efficient phases of flight, such as on the ground or at higher altitudes. Importantly, the transfer of delays out of the terminal approach area positions inbound flights to take advantage of Optimized Profile Descent procedures, where these have been implemented. The use of TBFM varies significantly by location, reflecting differences in operating environments and air traffic management strategies.

A predecessor of TBFM called Traffic Management Advisor (TMA) was developed and implemented in the 1990s. TMA was deployed at all 20 ARTCCs by 2007, and was modernized as TBFM in 2013 as a result of a major system re-architecture.

Time Based Flow Management

For arrivals to Philadelphia International Airport (PHL), Time Based Flow Management (TBFM) is used for arrival management, airborne metering, departure scheduling in arrival flow, and en route departure scheduling. TBFM is generally used during periods of high demand. It is used by each facility for various lengths of time, some more frequently and for longer durations than others. TBFM use is managed by PHL's Terminal Radar Approach Control (TRACON) facility. The Cleveland and Boston Air Route Traffic Control Centers (ARTCC), ZOB and ZBW respectively, schedule departures and provide airborne metering when needed. PHL TRACON schedules the New York ARTCC (ZNY) and Washington, DC ARTCC (ZDC) departures, while occasionally second tier facilities such as Indianapolis ARTCC (ZID) and Jacksonville ARTCC (ZJX) provide Miles-in-Trail support through the use of the en route departure capability.

The use of time-based metering with Traffic Management Advisor for PHL arrivals predates the NextGen program. However, the deployment of the modernized TBFM system in 2013 provided technical enhancements and a platform for additional operational benefits at PHL and other airports.

The FAA conducted an operational assessment of two Time Based Flow Management (TBFM) functions, airborne metering and departure scheduling, at eight airports (four per function) where these are used widely, including Philadelphia International Airport (PHL). The locations were selected based on how frequently each function is used alone and in combination, so the impact of each function could be measured. For this reason, results cannot be interpreted to be representative of impacts at other locations.

For each function, the assessment looked at the impact on both arrival delays and airborne delays as indicators of how efficiently available capacity was used. The FAA's assessment of flights between July 2011 and December 2013 found:

• For three of four airports studied that use Departure Scheduling, arrivals tended to experience 1.0 to 1.3 minutes less of arrival delay when the facility was using TBFM to schedule departures
• With few exceptions, departure scheduling also significantly reduced the variability of delays
• There is an 8 to 10-minute difference between the average arrival delay for metered flights and those subject to Miles-in-Trail (MIT) restrictions alone, for the four airports studied. It is unclear, however, how much of this difference can be attributed exclusively to TBFM because much of the difference occurs on the ground, and there could be other contributing factors.
• Metered flights experienced about a minute less airborne delay than those subject to MIT restrictions, as well as less extreme and more predictable airborne delays.

Click here for a full description of the NextGen Operational Performance Assessment.

The FAA estimates that the combined reductions in aircraft delays for the eight airports evaluated translated to about $640 million in savings between 2011 and 2014 (expressed in 2015 dollars). These savings reflect reduced operating costs to airlines of $209 million, and time savings to passengers valued at over $430 million. The estimate applies the average observed per-flight delay savings to the base of arrivals managed by airborne metering or departure scheduling in accordance with the FAA's performance assessment.

Time Based Flow Management (TBFM) is deployed at 93 facilities across the National Airspace System (NAS), including 20 en route, 28 terminal, and 45 tower facilities. It is deployed at all but two of the Core 30 airports, with Tampa International Airport (TPA) and Honolulu International Airport (HNL) as the two exceptions.

Read how Time Based Flow Management (TBFM) is used at other locations in the National Airspace System.