An Airspace Flow Program (AFP) is a traffic management initiative (TMI) that identifies constraints in the en route domain of the National Airspace System (NAS) and develops a real-time list of flights that are filed into the constrained area, distributing Expect Departure Clearance Times (EDCTs) to meter the demand through the area.
AFPs were introduced in 2006 and marked a significant new step in en route traffic management. The principal goal for the initial deployment was to provide enhanced en route traffic management during severe weather events. However, the use of AFPs has been expanded to other applications, such as managing excess volume during special events.
How Do AFPs Work?
As traffic managers monitor traffic volume in the enroute portion of the National Airspace System (NAS), they are constantly looking for areas where the amount of traffic exceeds what that piece of airspace can handle at that time.
To assist them in doing this, they utilize a tool called a Flow Evaluation Area (FEA), which is a function of the FAA’s Traffic Flow Management System (TFMS). Basically, an FEA is a line in space that is drawn across a specific area. Traffic managers can then monitor the amount of traffic crossing that line. The FAA’s Flight Status Monitor (FSM) application is used to help analyze the traffic volume and, if needed, model a program to help manage it. An “acceptance rate” is set for each FEA – the amount of traffic that ATC determines can be accepted through that airspace in any given hour, half hour, or quarter hour.
Once the amount of traffic reaches a point where it is considered to be a potential issue, the FEA becomes a Flow Constrained Area (FCA). At this point, traffic managers begin looking at possible ways of metering the traffic across the FCA, to ensure that it does not exceed what controllers can actually handle. This may mean that ATC issues miles-in-trail restrictions or reroutes designed to move traffic out of the constrained area.
If volume reaches a point where these initiatives are not sufficient, the specialist may decide to issue an AFP. Once this happens, specialists at the FAA Air Traffic Control System Command Center (ATCSCC) utilize the FSM application to model the AFP, much like they would a ground delay program (GDP). The AFP is designed to bring the amount of volume in each hour below the acceptance rate by delaying traffic, which is accomplished by issuing EDCTs.
Once an AFP is issued, the Command Center sends an advisory that is accessible in the Advisories Database. The AFP will also appear on the Operational Information System (OIS). EDCTs will be accessible on the FAA’s EDCT Lookup Page or through the operator’s flight plan service provider.
In situations where more than one TMI is being used simultaneously, it is important to understand their hierarchy.
- A ground stop is at the top of the hierarchy, since it is the most restrictive type of initiative and overrides any EDCT for an AFP or GDP. Note that, if a ground stop is lifted and the AFP is still in place, the flight will get a new EDCT for the AFP.
- A GDP is the second most restrictive program, so any EDCT for a GDP would override an AFP.
It is also important to note that the predicted demand through an AFP, and the weather impacting the area, may change substantially over time. When the conditions warrant, traffic managers will revise the AFP, in an effort to reduce delays. In a revision, AFP entry slots are recomputed so that demand is again metered to meet capacity and new EDCTs are distributed. AFPs are also subject to adaptive compression, which can cause an EDCT to change numerous times during a program.
Where AFPs Are Used
When AFPs were created, traffic managers quickly recognized several “trouble spots” where they would most often be used. This resulted in the creation of a set of pre-coordinated (known as “canned”) AFPs. These AFPs were designed to be implemented easily and with reduced coordination. Over time, additional canned AFPs have been created.
Currently, most AFPs are focused on severe weather events in the eastern half of the United States. Specifically, they are used when thunderstorms impact the NY metro and Boston metro areas, the Ohio Valley, Washington Center (ZDC), the DC metro region, or traffic in and out of Florida and the Caribbean.
AFPs are also used to manage increased volume, such as holiday traffic into Florida, Mexico and the Caribbean, and have been used to help manage significant equipment failures that result in loss of radar coverage and/or frequencies.
As AFP technology and procedures improve, it is expected that they will be utilized to manage airspace constraints throughout the NAS. This will result in the use of “ad-hoc” AFPs, which can be created and utilized anywhere in the NAS. If an ad-hoc AFP is created, it will be indicated on the OIS page, accompanied by a graphic representation and by an advisory.
Options to Avoid AFPs
To avoid the delays associated with an AFP, the options are fairly straightforward – adjust the flight times to before or after the AFP is in effect or route around the AFP (if possible).
Most AFPs will provide at least one option to route out of the program. Most of the time, these route-outs take the form of longer routes that will take flights around the horizontal boundaries of the program. However, route-out options are not alway available and are dependent on route availability and controller workload.
For example, when FCAA05 is in place, the Command Center will often coordinate Canadian routes with NAV CANADA that will allow flights to fly north of the AFP through Toronto Center (CZY) in order to fly into the northeast. This longer route will exempt those using it from their EDCTs issued to them for the AFP.
Another example can be seen when FCAA08 is in place, capturing northbound traffic from the south through Washington Center (ZDC). In this case, the offshore AZEZU routes may be made available, taking traffic out over the Atlantic, east of the AFP boundary, and exempting those flights from their EDCTs.
If an operator plans to use a route-out option, it is important to note that, when re-filing a flight plan with the new route, it MUST be filed exactly as it appears in the reroute advisory, which can be found in the Advisories Database or on the Current Reroutes web page. Otherwise, the automation will reject the route-out and place the flight right back in the AFP.
Occasionally, it is possible to fly under or over an AFP. However, since the floor of most AFPs is set between 12,000ft and FL180, this may not be a viable option for longer flights. The ceiling of most AFPs is usually set at FL600, making overflight impossible – but, in certain instances, the ceiling may be lowered to a more manageable altitude.
Aside from route-out options, operators should always be sure to submit their flight plan information to their flight plan service provider as early as possible, particularly when the use of AFPs is possible. This allows FAA to know about flights in advance, which helps with their planning. Conversely, when flight plans are submitted late, FAA treats these flights as “pop-up” flights. Because these flights can be disruptive to plans and programs already in place, the delays (in the form of EDCTs) issued to these flights can be more dramatic.