If you’ve traveled by plane, then you’ve likely experienced this dreaded scenario. You’ve embarked the plane, your seat is buckled, your bags are stowed, and you’re ready to get your trip underway – but instead, you’re stuck sitting on the runway waiting for the plane to take off.

With an increase in travel and flights surrounding the holidays this winter, flight delays were frequent and longer. Weather events and airport congestion only compounded the problem. According to AAA, 112.7 million people were scheduled to travel this past Christmas and New Year’s Day, an increase of 3.6 million people from the previous years. Even outside the busy holiday travel season, according to Flightaware.com, thousands of delayed and canceled flights occur daily in the United States. These types of delays can occur for several reasons, including weather, maintenance, and turnover time between flights. 

Susan Hotle, an associate professor in civil and environmental engineering, hopes to eliminate these lengthy delays. Prior to joining Virginia Tech, Hotle worked on flight delay analysis for the Federal Aviation Administration (FAA). Her current work concentrates on delays during taxiing, which is the time an aircraft sits in movement on the surface of an airport.

“My family did a lot of international travel during my childhood, and every time we entered an airport, I was fascinated with how many complex systems interacted and needed to be efficient for the overall system to work,” said Hotle.

Hotle recently created a tool to improve the efficiency of taxiing time. The Taxi Event Extractor (TEE) parses key metrics and events from flight radar data collected through the FAA’s System Wide Information Management feed. The project is funded through grants by the FAA’s NEXTOR III, an eight-university consortium in aviation operations research.

“My main goal is to improve estimates of unimpeded taxi times at airports in order to better quantify delays and aid in delay-mitigation strategies,” Hotle said. “Having minimized delays is important to all travelers.”

Hotle’s program provides data such as spatial temporal metrics of average speed, flight frequency, average flight weight, and total flight weight on airport surfaces, which all contribute to taxiing times. Other factors include limited runways available and airplane congestion, as well as maintenance and the elimination of ice from runways. The TEE model specifically supports the analysis and optimization of aircraft deicing times in the United States, which is the first study on this topic in the U.S. using radar data.

Hotle is working with the same airports to update U.S. airport layouts with data on aircraft trajectories. Currently, the FAA metrics on airport surface performance are based on times, such as actual or scheduled gate-out time and the scheduled, unimpeded taxi time. The use of airplane trajectories is a newer approach that Hotle is adding to her model to get a more complete analysis of delays. 

“Updating the layouts using airplane trajectories allows for an added spatial capability to the delay that will not break when the airport layout is modified with new or decommissioned runways and taxiways or expanded apron areas,” Hotle said. “Having updated layouts is also important as it differentiates the airline-based delays from FAA delays.”

Airlines control the operations in the apron area, or the place where airplanes are parked, and the FAA manages the operations within the taxiways and runways, Hotle said. Her team’s updated maps will help determine whose jurisdiction the delay occurred within and the causes of those delays. 

Heatmap of JFK Airport
Average taxi speed at John F. Kennedy International Airport across four days. Graphic courtesy of Susan Hotle.

Hotle’s research could benefit the aviation industry by providing quantitative evidence of when and where delays occur, thereby identifying major bottlenecks in the system. The program also will give researchers detailed taxiing speed and route information records to aid in robust simulations testing policies and procedures that can lead to more efficient airport operations.

Hotle analyzes other operational problems to identify characteristics that correlate with positive or negative outcomes. Her research investigates what types of flights result in the aircraft taking longer to recover its schedule after a major delay and what characteristics of an airport and its airlines can help predict if that airport is at risk of losing airline service in the future.

The average flyer might still find traveling stressful, as taxiing is such a small portion of the overall flight experience, but Hotle stresses that higher-level improvements to small inefficiencies in the taxiing process can lead to more proficient airport operations and significant environmental savings. 

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