Time Based Flow Management (TBFM)

TBFM, sometimes referred to as “metering,” is an air traffic management tool that seeks to schedule aircraft to an active runway threshold with the least amount of delay. The idea is to assign delays on the ground to prevent excessive airborne holding, thereby saving fuel and increasing safety.

How does TBFM work?

TBFM functions by assigning delays to all aircraft departing from within the same, or adjacent, center to a destination airport. The system looks at all the flights arriving at a certain airport, and then examines other factors in the National Airspace System (NAS).

Once the destination airport’s acceptance rate – the number of aircraft that can land each hour – is set, the computer uses detailed aircraft performance models, for each individual flight, to determine an aircraft’s estimated time of arrival (ETA) at the destination airport, given the current conditions.

Next, the program compares the ETA to the entire current airborne inventory (sometimes referred to as the “overhead stream”), along with other aircraft waiting to depart, and determines when those waiting aircraft will be allowed into the stream. Once this is determined, the system assigns a required departure time to the flight. Note that these are not Expect Departure Clearance Times (EDCTs) – EDCTs are only issued for delay programs, such as ground delay programs.

Once the flight is airborne, TBFM continues to do its job, tracking the aircraft in flight and advising ATC if it is ahead of or behind schedule.

What Operators Need to Know

The biggest concern for operators with TBFM is that there is, currently, no way to find out what an aircraft’s delay will be until the crew calls ATC for clearance to depart. Having a flight plan in the system in advance doesn’t help in this case, since the TBFM slot process is not initiated until the crew calls “ready to go.”

As a result, NBAA encourages operators to be actively aware of which airports are utilizing TBFM and whether it will impact their flights. One way to do this is to check the FAA Current Restrictions web page for references to “TBM” – a shorter abbreviation for TBFM. While this will not give actual delay information, it will indicate where and when TBFM is being used.

In addition, it is recommended that crews call for their departure time as soon as early as they can, remembering to brief passengers that possible delays could result from TBFM operations. While a TBFM required departure time will not be given until the flight is ready to depart, crews can call clearance delivery or ground control in advance to inquire whether metering delays can be expected.

TBFM is currently in use at many larger airports, with more coming online in the coming months. Eventually the FAA wants to use TBFM at all airports.