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Traffic Management Advisor (TMA)
TMA, also referred to as time-based metering, is a relatively new air traffic management tool that seeks to schedule aircraft to the 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 TMA work?
TMA functions by assigning delays to all aircraft departing from 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.
Once the airport arrival 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 the aircraft will be allowed into the stream. Once this is determined, the system assigns a required departure time to the flight.
Once the flight is airborne, TMA 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 TMA 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. Filing the flight plan early doesn't help in this case, since the TMA 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 TMA 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", which stands for time based metering. While this will not give actual delay information, it will indicate where and when TMA is being used.
In addition, it is recommended that crews call for their departure time as soon as they are ready to go, remembering to brief passengers that possible delays could result from TMA operations.
The TMA system is currently in use at many larger airports, with more coming online each month. Eventually the FAA wants to use TMA at all airports.