The intent behind traffic flow management (TFM) is to balance demand with capacity – both at airports and in airspace. In other words, air traffic managers try to ensure:
- There are not too many airplanes in one place at one time.
- The system is running efficiently.
Traffic management initiatives (TMIs) are techniques used by air traffic control to balance demand with capacity when conditions are not ideal, either at an airport, or in a section of airspace.
Ironically, operators who actually know about TMIs often associate them with delays. But, in reality, TMIs exist to minimize overall delays.
Airport-Specific (Terminal) TMIs
Some TMIs are designed to deal with the issue of too many airplanes arriving at an airport during a certain period of time. Each airport has a certain rate at which they can handle arriving traffic, known as the airport acceptance rate (AAR), which can change depending on weather, construction or other factors. If the number of airplanes heading to that airport are above that AAR, traffic managers must slow things down to keep it manageable.
Ground Delay Programs (GDPs)
A GDP is a TMI where aircraft are delayed at their departure airport in order to reconcile demand with capacity at their arrival airport. Flights are assigned expect departure clearance times (EDCTs), which ensure that they arrive at the affected airport when they can be accommodated.
GDPs will normally be used when an airport’s arrival capacity has been reduced by weather or other factors for a sustained period of time. Note that GDPs affect arrivals to a constrained airport, not departures from that airport. Also, they are airport-specific – each GDP only affects a single airport.
Ground delay programs affect all flights within the defined “scope” of the program. Learn more about scope and how GDPs work from NBAA.
Information about current GDPs can be found on the FAA’s Operational Information System (OIS) page.
Ground stops are the most restrictive form of TMI because they hold all aircraft, within the scope of the ground stop, at their departure airports until conditions at the destination airport allow for their arrival.
This type of TMI is typically used for shorter-term problems at an airport, such as an unexpected spike in arrival demand during a particular hour or thunderstorms affecting an airport.
Note that ground stops only affect arrivals to a specific airport (not departures) and, like GDPs, are airport-specific. Also, ground stops do not generate EDCTs. The stop simply continues until its “update time,” after which it is extended, expanded or canceled.
Occasionally, ground stops transition into GDPs if the constraint continues long enough. Learn more about how ground stops work from NBAA.
Traffic Management Advisor (TMA)
TMA, also known as time-based metering, is a newer technology that is designed to provide a precisely timed stream of traffic to a specific airport threshold or arrival fix, allowing the airport to accept arrivals at it’s peak capacity.
It does this by assigning delays, similar to EDCTs, to aircraft departing from airports relatively close to the destination, usually from En Route Centers immediately adjacent to the destination Center.
While it is very effective in controlling traffic to an airport, there are some drawbacks to the system. TMA delay times are not issued to aircraft until they actually call for clearance. This means that operators don’t know what their delay will be until they try to depart.
At this time, the best option for operators is to know where and when TMA is being used and to communicate proactively with ATC (clearance delivery or ground control) to determine the severity of the TMA delays.
New technologies are being developed to allow operators to find out about these delays further in advance. Learn more about how TMA works from NBAA.
En Route TMIs
Some TMIs are designed to prevent too many aircraft from moving through a particular piece of airspace (in the en route environment) at one time. When this happens, traffic managers need to slow things down and/or spread the traffic out in order to prevent airspace congestion.
When conditions require air traffic to be moved away from, or into, a particular area of airspace, traffic managers will implement reroutes – either optional or required – to optimize the flow of traffic.
There are three main types of reroutes that FAA uses, depending on the circumstances:
- Preferred routes are the routes that ATC would like you to file if there are no constraints on the system.
- National Playbook routes are a set of pre-planned routes that can be quickly implemented by ATC in order to help move traffic out of a constrained area, whether it is an en route or terminal constraint. These routes can be issued in one of 3 ways:
- Required – Aircraft meeting the parameters of the reroute MUST file the routes as issued.
- Recommended – These routes are where ATC wants operators to be, but are not required.
- FYI – These routes are available to be used if the operator chooses to do so.
- Coded Departure Routes (CDRs) are another type of route, identified by an eight-character code, designed to quickly and concisely issue a full route clearance that may be different than the originally requested route.
Special attention should be given to required reroutes, since those are routes the operators MUST be filed on. In other words, if there is a required reroute in place between TEB and PBI, the operator must file that route exactly as it is published. Not doing so flags ATC that the flight is non-conformant and requires additional action to make the correction.
Information about what reroutes are in place can be found on the FAA’s Current Reroutes page.
Miles-in-Trail / Minutes-in-Trail
When traffic needs to be spaced out along a particular route, traffic managers will very commonly use a technique called miles-in-trail (MIT) or minutes-in-trail (MINIT). This involves slowing down or speeding up traffic to maintain a certain amount of space (or time) between aircraft, usually to allow room for tactical deviations around weather or to address sector controller workload issues.
Much like TMA, MIT or MINIT will result in a delay being issued on the ground at their origination airport to maintain this spacing. However, there is a way for operators to determine if miles-in-trail is being used along their route of flight on the FAA’s Current Restrictions page.
Airspace Flow Programs (AFPs)
When a significant constraint occurs in the enroute portion of the NAS, traffic managers often need to measure, and potentially control, traffic through a particular area. In order to do that, they use something called an airspace flow program or AFP.
An AFP is, in essence, a line drawn in space in association with a constraint, usually convective weather. It begins as a flow evaluation area (FEA), and if conditions warrant, becomes a flow constrained area (FCA). If the decision is made to actually control traffic across the line, the FCA becomes an AFP.
Once this happens, any flights filed across the line (usually only in one direction) are assigned expect departure clearance times (EDCTs), to ensure that they arrive at the AFP line, or “boundary,” at a time when they can be accommodated.
As the constraint worsens or improves, the “throughput” across the AFP can be adjusted, decreasing or increasing the number of flights across the line and lengthening or shortening the delays.
How Do I Find Out What TMIs are Being Used?
As you can see above, there are easy-to-access ways for operators to find out what TMIs are currently being used by the FAA. The key thing to note is that you do not need to wait until you are in the airplane, ready to depart, to find out about TMIs that might affect your flight.