How Do Air Traffic Controllers Determine the Sequence of Takeoffs?

Managing the flow of flights at an airport requires a complex coordination effort between air traffic controllers and pilots. The order in which planes take off can vary based on multiple factors, including the airport's activity level, air traffic control procedures, and weather conditions. This article provides an in-depth look at the decision-making process behind determining the sequence of takeoffs at both busy and less busy airports.

The Role of Air Traffic Control in Managing Takeoffs

At busy airports, flights often have a scheduled wheels-up time at the origin airport, which is designed to fit into the operational flow at their destination. This means that planes may have to wait a few minutes at the end of the runway while other flights to other destinations depart ahead of them. This is managed by air traffic control (ATC) to ensure efficient operation and safety.

First Come, First Served

At less busy airports, the process is often simpler and follows a 'first come, first served' principle. Whoever gets to the start of the active runway first goes first. However, even in this scenario, air traffic controllers may make exceptions based on various factors, such as aircraft readiness or airspace limitations.

Priority and Safety Considerations

When the aircraft at the front of the queue is not ready to go, air traffic controllers may let aircraft behind it take off first, assuming the front aircraft is not blocking the only entrance point to the runway. This decision ensures that the aircraft with the most passengers (such as a B747 with 400 passengers) has priority over those with fewer passengers, like a Cessna 172 carrying 4 people on a short trip. This prioritization also helps avoid separation issues, where a larger aircraft might need to overtake a smaller one immediately, posing potential risks.

Sequencing Requirements and Capacity Maximization

At very busy airports and in congested airspace, sequencing requirements come into play. This means that aircraft departing in the same direction need to be spaced about 5-7 miles apart, effectively allowing a departure every two minutes. However, if the path of the following aircraft is at least 15 degrees different from the one in front, the second aircraft can take off as soon as the first is in the air and at least 6000 feet in front. This doubles the capacity of the runway significantly. For RNAV (Area Navigation) Standard Instrument Departures, where navigation is done using GPS or INS, this angle can be relaxed to 10 degrees.

Observing the Process at a Busy Airport

A great example to observe this process is at a busy airport like Atlanta. The ground controller carefully schedules the aircraft taxiing to the departure runway, creating what appears to be a long queue from an untrained observer's perspective. However, the arriving aircraft are actually carefully ordered so that each is sequenced by destination and the Standard Instrument Departure path they will follow, ensuring a minimum 10-degree difference in heading between all aircraft. Doing this consistently can allow an aircraft to depart every 45-60 seconds, resulting in significant operational efficiency and satisfaction among passengers, pilots, airline shareholders, and ATC bosses.

Conclusion

Understanding how air traffic controllers determine the sequence of takeoffs is crucial for appreciating the complexity of airport operations. By following well-structured procedures and utilizing modern navigation technologies, ATC ensures both safety and efficiency in managing thousands of flights daily, even in heavily congested airspaces.