Tools Used for Traffic Flow Management

Traffic Management Initiatives (TMIs) are programs and tools that ATC may use to manage air traffic. These initiatives can take a number of forms, depending on the need and situation. Some TMIs are used to manage excess demand or a lowered acceptance rate at a particular airport. Other TMIs are used to manage traffic issues in the en route environment. TMIs can generally be divided into 2 categories – terminal and en route.

Terminal TMIs are airport-specific, in that they directly impact arrivals into a particular airport. This is contrasted with TMIs like Airspace Flow Programs (AFPs) which can affect numerous airports due to en route issues.

It is important to note that terminal TMIs are airport-specific. For example, if there is a ground stop or ground delay program (GDP) at White Plains, NY (HPN), flights to Morristown, NJ (MMU) would not affected by that TMI.

Enroute TMIs, as their name implies, are used to manage air traffic in the en route segment of flight. The only en route TMIs that can generate EDCTs for a flight are AFPs and Collaborative Trajectory Options Programs (CTOPs). AFPs behave in a similar fashion to GDPs, but control flights into a particular block of airspace instead of a particular airport.

The remaining en route TMIs can generate flight delays either before departure, or while enroute. In most cases, these manifest themselves as departure delays or enroute speed restrictions.

Commonly Used Traffic Management Initiatives

While there are quite a few TMIs that traffic managers can utilize on a daily basis, there are several that are commonly used and that operators should be the most familiar with.

Ground Stop (GS)
A Ground Stop is an initiative requiring aircraft that meet specific criteria to remain on the ground at their origination airports due to a constraint at their destination airport. They are generally used for relatively short-term constraints, lasting 2 hours or less. Ground stops are the most restrictive form of TMI.

Ground Delay Program (GDP)
A Ground Delay Program (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 departure times, which in turn regulate their arrival time at the impacted airport.

Airspace Flow Program (AFP)
An AFP is a TMI that identifies constraints in the en route environment, develops a list of flights that are filed into or through that constrained area, and distributes expect departure clearance times (EDCTs) to meter the demand through the area.

Miles-in-Trail (MIT)/Minutes-in-Trail (MINIT)
Miles-in-trail describes the number of miles required between aircraft departing an airport, over a fix, at an altitude, through a sector, or along a route. MIT is used to apportion traffic into a manageable flow, as well as provide spacing for additional traffic (merging or departing) to enter the flow of traffic.

Time Based Flow Management (TBFM)
TBFM, otherwise known as metering, is a relatively new 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 holding, thereby saving fuel and increasing safety.

Reroutes & Severe Weather Avoidance Plan (SWAP)
When air traffic needs to be moved away from or into a particular area of airspace, traffic managers will implement reroutes (either optional or required) that move traffic to specific routes needed for optimized traffic flow. A specific application of reroutes is known as the Severe Weather Avoidance Plan (SWAP), which is a formalized program that is developed for areas susceptible to disruption in air traffic flows, usually caused by thunderstorms.

Additional Terminal TMIs

Special Traffic Management Program (STMP)
An STMP is a set of planned traffic management procedures implemented to effectively manage the increased air traffic demand expected for a special event. STMP NOTAMs are issued in the Notices to Airmen Publication (NTAP).

High Density Traffic Airports (HDTA)
There are certain airports that require unscheduled operations to acquire a reservation prior to operating at the airport. These airports include Ronald Reagan Washington National Airport (DCA) and LaGuardia Airport (LGA).

Additional Enroute TMIs

Collaborative Trajectory Options Program (CTOP)
CTOP is a new type of TMI that automatically assigns delay and/or reroutes around one or more airspace constraints in order to balance demand with available capacity. The unique feature of CTOP is that it allows for user preferences in route selection.

Other En Route Tools
There are additional tools that traffic manager use to manage en route traffic. These tools include:

• North American Route Program (NRP)
• Flow Evaluation Areas (FEA)/Flow Control Areas (FCA)
• Capping
• Tunneling
• Integrated Collaborative Rerouting (ICR)
• Low Altitude Alternate Departure Routing (LAADR)

TMI Hierarchy

In many cases, more than one TMI can capture a particular flight at the same time. In those instances, there is a set hierarchy to determine which TMI will be enforced for that flight. On a basic level:

• Ground stops always take priority over any other form of TMI. In other words, a ground stop will supersede an EDCT or required departure time.
• TBFM, or other metering required departure times, always take priority over EDCTs.
• EDCTs from GDPs always take priority over EDCTs from AFPs or CTOPs.

Review the FAA TMI Interaction document.

Compliance

All aircraft that meet the specified criteria (scope) of a TMI are included by default. Aircraft that are impacted by a TMI and require priority handling because of some special circumstance may be accommodated if possible.

In addition, while operators are expected to comply with issued TMIs, FAR Parts 91, 121 and 135 dictate that all operators have the right of refusal of a specific clearance and may elect an alternative. Alternatives include, but are not limited to, ground delay, airborne holding, diversion to another airport, or a request to stay on the filed route.

In the case of a GDP or an AFP, non-compliance with the TMI can result in an overabundance of aircraft or in unused slots that cannot be filled at the destination airport or volume of airspace. This can cause holding, diversions, or TMI revisions and extensions – all of which lead to more delay. In short, everyone pays the price for non-compliance.

More information regarding what TMIs are currently in effect in the NAS can be found on the the FAA OIS web page, which provides near real-time status information about the NAS. Pilots may also receive information through their flight plan service provider. Learn more about OIS.