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Friday morning started with delays at LaGuardia Airport in New York. This is not unusual, New York airports are famous. But this time, the cause was not something prosaic, like a blizzard. It was staff. Due to the closure of the federal government, the airport did not have enough security officers in transportation security or air traffic controllers; things slowed down until a stop on the ground.
Then it began to spread – Newark, Philadelphia, even the key Atlanta center have all started to collapse. And it's terrifying. Airports are nodes of a global network, and the science that guides the behavior of this network means that if a node has a problem, it spreads. The international air transport network is at the forefront of technology. It does not take much to get it out of the optimal flow.
Basically, the problem of delays is that of "connected resources"; The planes land and have to turn around to make other flights. Some pbadengers also take other flights. If you've ever flown, you know all that, but what this means in practice is that small errors or delays in an airport are magnified as they move forward, spread, and intensify at times. "The systems running these queues are very close to their capacity," says Hamsa Balakrishnan, an aerospace engineer at MIT, who studies the air transport network. "LaGuardia and Newark have experienced wind delays today. With a full staffing that you could have managed, but with a decrease in staffing, you also have delays, which end up extending to other airports as well, because of the connectivity . "
In general, it can be expected that the largest airports in the world, those with the highest number of round-trip or pbadenger-carrying flights, will have the greatest impact on overall movements on the network. But in reality, the "airport delay multiplier" varies depending on all things, from the way an airport is planned, to its overall capacity and even weather conditions. According to one calculation, one minute delay causes an average of 30 seconds of slowdown elsewhere on the network. But some airports are more resilient than others. The time it takes to go from one to the other has an effect. It's so complicated that it discourages even the most intrepid network modellers.
Airlines are trying to take all of this into account by creating time out. They calculate the time that a flight should last – the "expected flight time" – and the time the plane should go to ground, the "expected turnaround time". But then they have the choice. "They are inserting a buffer time into their schedules and ground operations," says Bo Zou, transportation engineer at the University of Illinois. "They still face delays, and a newly formed delay for a flight spreads to the second and third flights. Part of it will be absorbed by the buffer, but not all. »Build a buffer that is too small and delays spread further. Build a buffer zone too important to not use your fleet efficiently and lose money. "One is efficiency, the other is robustness," says Zou.
And that changes all the time, depending on the changing conditions. Some are predictable, such as winter storms, other no, like government shutdowns and informal sick leave. This is called a "dynamic complex network". He has to adapt constantly.
Because if it is not? According to one study, flight delays cost the US economy more than $ 30 billion a year. It's not just time lost or flying costs; that's what the pbadengers on these flights planned to do when they arrived. "A prolonged shutdown, or even a slowdown, would probably have consequences for all sorts of unexpected events," says Luís Bettancourt, network researcher at the University of Chicago. "The reliability of the urgent logistics will deteriorate and the hub character of some of these cities will have to be bypbaded, at least temporarily. A prolonged slowdown would be very disastrous for big cities, their influence and their economies. "
After shutting down, the government can now return its TSA officers and air traffic controllers. This will allow airports to gain resilience just in time for a big snowstorm that should hit the Midwest next week. But the overall health of the air transport network will always be precarious.
This is why researchers are trying to accumulate more and more data on how everything works (or does not work). If humans can not program all these flights efficiently and robustly, an algorithm can do it. Balakrishnan even co-founded a start-up that is trying to make it a reality. "There are so many moving things that it's hard for a human being to come up with all the possible solutions," she says. "But it's something we know how to make computers work." If you now like to fly on an intractable and incomprehensible network, wait for it to be handled by an insoluble, incomprehensible robot.
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