Tools Used for Traffic Flow Management

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General Aviation Airport Program (GAAP)

Introduced in late 2004, GAAP is a type of GDP designed to allocate arrivals in an equitable manner to an airport in a high demand situation, such as the NBAA conference or Indianapolis 500 Race. It improves predictability and reliability for all operators – scheduled and unscheduled.

The significant difference between a traditional Delay Assignment (DAS) GDP and a GAAP is the way in which delays are assigned to flights that are unknown at the time of program implementation.

Why Not STMP?

Traditionally, airport peak demand situations driven by special events are handled by STMPs where operators must obtain arrival reservations as early as 72 hours in advance. Because this method is highly restrictive on operator flexibility, it is not a preferable method to deal with other airport high-demand issues that are not related to specific peak events.

For example, during the winter months unscheduled traffic dramatically increases to Florida airports, especially to and from the Northeast. At the same time, scheduled carriers also increase their flights to these popular winter destinations. This “Snowbird” trend often causes airports - such as FLL and PBI - to have combined scheduled and unscheduled demand that will exceed the airport’s capacity regularly from November through April. This situation can cause heavy arrival and departure delays, ramp gridlock, and airspace congestion. This surge is not tied to a specific peak event and therefore a STMP is not considered a viable option by NBAA. A better solution that NBAA supported and assisted in developing is the GAAP tool.

How is a GAAP different from a traditional DAS GDP?

Traditional DAS GDPs are implemented when demand already exceeds capacity. These are commonly seen at airports such as SFO, ORD, EWR, ATL where the majority operators are scheduled carriers.

Scenario 1:
An airport at a VFR airport arrival rate (AAR) can land 35 airplanes per hour and operates at that rate on a regular basis. When the AAR is reduced due to an airport or a system constraint from 35 arrivals to 30 arrivals per hour the demand on the airport is still 35 or 5 flights over the hourly capacity.

When this scenario occurs, a GDP is issued using an automation tool called Flight Schedule Monitor (FSM). FSM looks at all of the known demand (scheduled flights and filed flight plans that have reached the Enhanced Traffic Management System (ETMS) via the Host) and uses an algorithm to smooth the demand from the 35 rate to the 30 rate. Because the airport was already in a situation where demand exceeded capacity, every “slot” is filled once the rate is lowered to 30 and delays are issued to all of that known demand. FSM assigns the same average delay to all of the known flights. This delay time is called an Estimated Departure Clearance Time (EDCT) and is essentially an Estimated Time of Departure (ETD) to the constrained airport adjusted for delay.

Does this mean that since there are no more arrival “slots” that other aircraft cannot file to that airport?

No. Because FSM only looks at known demand at the time of the GDP implementation it cannot account for the unscheduled traffic flight plans that have yet to reach the FAA Host system. Even if these flight plans are filed 3-4 hours in advance by the operator, often they do not reach the host until 90 minutes prior to departure due to Host automation issues that require long-term automation changes to fix.

Then how are those flights integrated into the known demand?

As a new flight or “pop-up” becomes known, FSM analyzes the average delay of known flights in the 15-minute arrival windows before and after the new flight. The new flight is then assigned an EDCT with that average delay and forced into the program. So, even if FSM originally smoothed the demand to only 30 arrivals per hour, the new flight can push that demand above 30 again putting the airport in a situation where demand exceeds capacity. When this happens in bulk, an ATC Specialist uses FSM to revise the program to account for the new flights or the new known demand. All of the flights are smoothed again to the 30 rate, new EDCTs are issued to all of the flights, and everyone’s delays increase from their original delay assignment. This makes it difficult for any operator – scheduled or unscheduled – to rely on their issued EDCTs since they may change frequently based on the amount of “pop-ups” that enter the program after it is implemented. This method often results in an over-delivery, which may cascade into further initiatives such as Ground Stops or increased miles-in-trail further deteriorating predictability.

Can GAAP address that issue?

In certain scenarios, the answer is yes. GAAP is specifically designed to manage any airport in which demand does not exceed capacity, but is expected to due to an increase in unknown or “pop-up” traffic. Therefore, GAAP would not be the appropriate tool to handle the earlier described Scenario 1 but may be appropriate for Scenario 2.

Scenario 2:
An airport at a VFR airport arrival rate (AAR) can land 35 airplanes per hour and operates at that rate on a regular basis. On a VFR day, demand is forecast, based on historical and anecdotal information, to exceed normal levels and may potentially approach or exceed the 35 AAR at times. Known demand accounts for 15 of the 35 hourly arrivals and unscheduled unknown demand is expected to make up the difference. A GAAP is issued at a 35 rate.

So how does GAAP work?

A GAAP is issued when known demand is less than the airport arrival rate. GAAP compares known traffic to airport capacity and allocates arrival slots to the known flights, scheduled or unscheduled, which may result in minimal delay, but it also generates a list of unassigned slots, which are held for future flights that are unknown to the ETMS at the time of implementation. All IFR flight plans that enter the system after implementation of the program will be assigned the first available unassigned slot at or after their requested time of arrival. The maximum GAAP delay a flight may receive is 360 minutes; however this is a configurable parameter and may be reduced if deemed appropriate. For example, if new traffic is getting 360 minutes of assigned delay and all others in the program are averaging 12 minutes; this would not be acceptable and the maximum delay limit may be reduced.

GAAP is most effective when it is implemented early on the day of expected increased demand to maximize slot availability and predictability. Also, to reduce excessive maximum delay assignments at the end of the expected peak demand time frame, GAAPs are most effective when the time of program expiration is hours past the time of expected peak demand.

GAAP is not designed to be used when demand is at or above capacity for any extended period of time, as described in Scenario 1, because there will be limited availability for unassigned slots. If airport demand eventually exceeds capacity the program may be revised to a DAS GDP as described in Scenario 1, resulting in new controlled times for all known demand, scheduled or unscheduled.

GAAP cannot always be used instead of a STMP because GAAP is only effective at managing IFR traffic. Events that attract heavy VFR traffic are better handled with the STMP tool. Also, GAAP is not viable for airports where demand excessively exceeds arrival rate, such as Eagle (EGE) where there are only 4 slots allocated during IMC conditions and hundreds of operators competing for those slots at once.

Typically, GAAP will be considered for use each day during events such as the NBAA Annual Meeting and Convention in Orlando, the Super Bowl, the Daytona 500 and other such events that draw high numbers of IFR traffic where demand may exceed capacity for an extended period of time.  A decision to implement a GAAP during a peak event will be made daily by ATC with the NBAA GA Desk Staff’s input. If one is implemented then it will be posted at www.fly.faa.gov/ois.

As with a traditional GDP, the flight's Estimated Departure Clearance Time (EDCT) can be found at www.fly.faa.gov/edct if a GAAP is in place. When a flight is destined to an airport with a GAAP in place, it will always be issued an EDCT even if it matches the original departure time. The crew must taxi in a manner to comply with your EDCT within +/- 5 minutes.