Traffic Management Initiatives: GDP, AFP, MIT, CTOP

A Ground Delay Program (GDP) is a traffic management initiative (TMI) issued when arrival demand at an airport exceeds the Airport Acceptance Rate (AAR) — the hourly rate at which the airport can accept landings. Affected flights are held on the ground at their origins so that the arrival queue fits within the reduced capacity.

The queue is divided into evenly spaced slots. The slot interval is

$$\tau = \dfrac{60}{R} \text{ minutes,}$$

where $R$ is the controlling rate in flights per hour ($R = \text{AAR}$ for a GDP).

Slots are filled by Ration-By-Schedule (RBS): the flight with the earliest original ETA gets slot 1, the next-earliest gets slot 2, and so on. If $T_0$ is the program start time, the Controlled Time of Arrival (CTA) for the flight in slot $k$ is

$$\mathrm{CTA}_k = T_0 + (k-1)\,\tau,$$

and the flight's ground delay is

$$\text{delay} = \mathrm{CTA}_k - \mathrm{ETA}.$$

An Airspace Flow Program (AFP) applies identical RBS math, but to a Flow Constrained Area (FCA) in en-route airspace rather than to an airport. The rate $R$ is then the FCA's hourly crossing rate, and the CTA is the controlled time at the FCA boundary.

For instance, an AFP with $R = 40$ flights/hr has $\tau = 60/40 = 1.5$ min. The flight in slot 5, with program start 18:00, receives

$$\mathrm{CTA}_5 = 18{:}00 + 4(1.5\text{ min}) = 18{:}06.$$