ORNL Review: Aviation Research Takes Off at ORNL

Aviation Research Takes Off at ORNL

Late landings. Canceled flights. Airplanes idling on runways as pilots wait for the signal to depart. For the second straight summer, passengers flying on U.S. airlines endured an increasing number of flight delays, sometimes having to miss scheduled events or sleep overnight in air terminals. Why is air traffic approaching gridlock? Reasons given are the increasing number of passengers and flights as a result of lower fares, severe thunderstorms, insufficient runway space, airline employee strikes, and an antiquated air traffic management system. Yet, the national air system has excelled in keeping big jets from flying into one another.

In 1991, when Lee Berry, Jim Rome, and other ORNL researchers began analyzing air traffic operations for the Federal Aviation Administration (FAA), they predicted that the worst air congestion at the end of the decade would occur over the Cleveland, Ohio, area. "That has proven to be the case," says Teresa Rose, program manager for aviation research at the National Transportation Research Center.

According to Rose, the ORNL group hopes to help the FAA reduce "en route airline congestion" by developing a computer model. Berry, Rome, and Ron Lee have received FAA funding to develop a model to predict the probability of airplane delays for different sectors of air space.

"We will look at ways to avoid delayed landings caused when airplanes are forced to take a longer route to better space out planes headed for the airport," Rose says. "The model will take into account severe weather, flight delays, and increased spacing of plane arrivals and departures to allow air traffic controllers time to adjust to upgraded equipment. Our model should help airlines select better flight times and routes to reduce en route delays."

ORNL researchers have completed several studies of air traffic congestion. With American Airlines, they modeled delay propagation by simulating delays and introducing the concept of a delay multiplier. "A flight that arrives late delays not only its passengers but also the crew and equipment needed for later flights, causing 'downstream' delays," Rome says. "A minute of delay occurring early in the day can cause over 10 minutes of downstream delay."

At major hubs an airline might have hundreds of landings in a day. Using data from Northwest Airlines and assisted by Lockheed Martin Management and Data Systems, Simon Rose, Rome, and Lee performed a cost-benefit study for NASA to determine whether the airline might save money by swapping landing slots among its own flights. During the final descent phase of flight, planes can speed up or slow down by as much as 10 minutes to enable these swaps.

"Moving a flight a few minutes can mean the difference between lots of missed connections and just a few missed connections involving both passengers and crew members," Rome says. "Changing a flight from 30 minutes late to 20 minutes late can remove delay costs entirely."

For the study, cost models and an optimum resequencing algorithm were developed. Using the results of the study, the ORNL researchers concluded that the U.S. airline industry would save $75 million a year if this strategy were operationally feasible. About 30% more would be saved if unused landing slots were employed.

To increase their numbers of daily flights (airport capacity), many airports used the controversial practice of allowing one aircraft to land on one runway and stop short of a second, intersecting runway, permitting another plane to simultaneously land on or take off from that runway. In 1999 the Airline Pilots Association (ALPA) opposed this practice as being potentially unsafe and threatened a boycott unless the safety margins were increased. Berry recently provided a better estimate of the cost of eliminating the procedure and, thus, allowing fewer flights. This estimate improved the basis for making decisions about trade offs between increased safety margins and reduced airport capacity. The arguments were presented to the major airlines' operations managers, ALPA, and the FAA. FAA and ALPA worked out a compromise that both improved safety margins of such simultaneous operations and retained much of the increased capacity.

Aviation safety is being studied by ORNL researchers Joe Cletcher, Gary Mays, Mike Poore, and Simon Rose. They are applying techniques developed for the nuclear industry to aviation. The goal is to identify accident precursors by coding the chains of events that contribute to aviation accidents and incidents.

This sample of airplane landings at Los Angeles International Airport shows an example go-around flight that occurs when a pilot is informed that the airplane is coming in too fast at the wrong angle—what is known as a "missed approach."

In another safety analysis study for the FAA, Berry worked with Austin Digital, Inc., to identify situations that could lead to safety problems, such as missed approaches to runways (e.g., an airplane coming in too fast at the wrong angle). The collaborators modified digital flight data analysis software (used for "black box" data) so that it could analyze radar data. They demonstrated its use to high FAA officials in March 2000. "This tool," Rose says, "is the first to use radar data for safety analyses."

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