In cases of congestion or adverse weather conditions, aircraft may sometimes circle for 10 to 30 minutes above the airport while waiting for their turn to land.
If you’ve ever wondered why pilots announce they are about to land, yet the aircraft seems to be flying in circles with no runway in sight, you might be in a holding pattern, according to CNN. This can occur for various reasons, primarily due to congestion and bad weather, often caused by reduced visibility, strong winds, and heavy snowfall. However, issues like equipment malfunctions or obstacles on the runway can also lead to this situation. It is one of the easiest ways to manage a surge in traffic around an airport.
Holding patterns are a way to manage air traffic congestion. (Photo: Sudden Widow Coach).
“When you’re driving and encounter a red light, you stop. But for airplanes, there’s no such option,” explains Junzi Sun, a professor of air traffic management at Delft University of Technology in the Netherlands. “You can think of a holding pattern as a type of traffic light for airplanes, used to control the flow of traffic into the airport.”
A holding pattern is a predetermined airspace where aircraft fly in a circular or oval path for a period of time to delay landing on the runway. According to Sun, planes continue flying in circles until air traffic control grants them permission to land. This is a standard procedure, and pilots do not need to maneuver manually, as guidance systems help the aircraft maintain the holding pattern.
Holding patterns serve as a lifeline at chronically congested airports. However, they come at a steep price. The primary issue with holding patterns is fuel consumption. “Holding patterns are a very inefficient way to fly because you have to maintain altitude, which burns more fuel. For this reason, it is a last-minute solution for air traffic control. There are many other, more efficient methods,” Sun states.
Flying at lower altitudes consumes more fuel due to increased air resistance, leading to higher emissions. Holding patterns are also quite noisy as they occur at altitudes of 7,000 to 13,000 feet, meaning engine noise can be heard on the ground. Ultimately, circling the airport instead of landing increases flight times by 10 to 30 minutes.
Alternatives to holding patterns, such as “linear delays,” require aircraft to fly slower or take longer routes before arriving. One form of linear delay is the point merge system, invented by Eurocontrol, the organization coordinating air traffic management in Europe. First used in Oslo in 2011, this system currently operates at about 40 airports worldwide, including Istanbul, Shanghai, and Tokyo.
Accordingly, all arriving aircraft converge toward a dome shape, only separating horizontally. At the right time, planes are allowed to enter the dome and continue to the merge point. After that, all aircraft follow the same route to the runway. The advantage of this method is that the dome can be at a higher altitude, up to 20,000 feet, away from residential areas, helping to reduce pollution and noise.
While holding patterns are very safe and have not resulted in fatal accidents for decades, issues can arise if an aircraft is delayed for too long. The biggest risk is fuel. If an aircraft is running low on fuel for any reason, it will need to make an emergency landing. Aircraft in such situations often declare an emergency, which may allow them to bypass the queue for landing or be prioritized for diversion to a nearby airport.
A hotspot for holding patterns worldwide is London, which has six major airports, including one of the busiest in the world, Heathrow. Not only does Heathrow have two runways while handling high traffic, but it also has a large number of international flights, making holding patterns more common.
