Safety and Tech Dept.: Time Based Flow Management
Thursday, January 17, 2013

By Steven Lee (Boston Center)

Time-based metering and the Traffic Management Advisor (TMA) is a process and air traffic control decision support tool that continues to evolve. As we move into 2013, new hardware and software enhancements to the time-based metering platform will be brought to the field. Along with the newly-deployed hardware, the TMA will be renamed and referred to as Time Based Flow Management (TBFM). The current TMA functionality will exist within the evolving TBFM system.  

At its core, TBFM is a scheduling tool that calculates estimated times of arrival (ETAs) and assigns scheduled times of arrival (STAs) to aircraft at a point in space. Information defining “stream class” settings and airport arrival settings are configured in the TBFM system to identify a designated fix or route, miles-in-trail requirement, aircraft class, and airport or TRACON arrival rate. Route analysis and trajectory calculations are performed using these defined settings along with flight plan and track data, wind data, airframe information, and airspeed and airspace constraint information producing the ETAs and STAs used for time-based metering.  

TBFM is currently used on a regular basis throughout the National Airspace System (NAS). Although TBFM is often thought of as an arrival-sequencing tool, the Enhanced Departure Capability (EDC) function proved a significant contributor to improved efficiencies in the NAS. Used as either an arrival or departure spacing tool, TBFM helps smooth out irregularities in traffic flows and manage demand/capacity imbalances.

TBFM continues to expand and develop additional functionality that will improve its accuracy and reliability. Coupled Scheduling (CS) is one such metering enhancement that allows for expansion of the metering environment while addressing some of the sequencing and delay issues found in today’s TBFM system. Currently in TBFM, the arrival system freeze horizons (point in space where an aircraft is locked in or “frozen” in a sequence) have in some instances been stretched beyond their practical limit; this has been done for valid reason due to airspace and/or flow configuration issues but can contribute to sequencing and metering delay allocation inaccuracies.

CS addresses this issue and extends the practical range of metering by providing the capability to adapt a tier of meter points, linked to an arrival metering system in a feedback control loop. This allows the TBFM system to consider and distribute the downstream meter delays to upstream meter points, thereby improving the overall scheduling and sequencing problem. CS was introduced and field-tested in 2011 at Oakland Center (ZOA) and Los Angeles Center (ZLA). Although the functionality performed as expected, there were command and control issues between the participating facilities that are currently unresolved.

Additional enhancements to improve and expand the time-based metering environment continue to be developed. Extended Metering (XM) and Integrated Departure /Arrival Capability (IDAC) are two utilities of the TBFM platform that are well into the development phase and should be introduced into TBFM within the next two years. XM will further increase the range and flexibility of TBFM through a collection of extensions and modifications to existing TBFM architecture and functionality. Integrated Departure/Arrival Capability (IDAC) will be a scheduling platform used to support departure planning and scheduling by providing a common situational awareness for towers, TRACONs and ARTCCs to see the same system constraints regarding airport configurations, departure status, available routes, slot availability and weather issues. IDAC development and implementation will occur in a phased approach and will improve and expand the existing functionality of Enhanced Departure Capability (EDC). IDAC will also provide the capability to automate the phone-based approval process.

Future TBFM enhancements also include:

  • Integration of Ground Interval Management-Spacing (GIM-S), which will provide en route controllers with speed control advisories linked to meter times.
  • Descent advisory tools that will advise aircraft and controllers as to where and when to initiate descent to the meter fix.
  • Terminal sequencing and spacing functionality that will provide advisories for efficient sequencing and runway assignments in the terminal environment.

TBFM has become an integral component of the NAS and continues to evolve toward the NextGen vision of gate-to-gate management of air traffic flows and sequencing.