Federal air-traffic controllers' union members protest the partial government shutdown at the U.S. Capitol in Washington, D.C.Jonathan Ernst / Reuters

Flight delays and service interruptions at American airports went from being a possible pressure point in the seemingly endless government shutdown to its stark reality Friday morning, after the Federal Aviation Administration temporarily halted incoming flights at New York’s LaGuardia Airport due to an air-traffic-control staffing shortage. House Speaker Nancy Pelosi seized the moment.

“The #TrumpShutdown has already pushed hundreds of thousands of Americans to the breaking point. Now it’s pushing our airspace to the breaking point too,” she tweeted at 11 a.m., calling on President Donald Trump to “stop endangering the safety, security and well-being of our nation. Re-open government now!” The president did not address the aviation issues, instead tweeting a half hour later about the arrest and indictment of his longtime adviser Roger Stone, once again complaining about Special Counsel Robert Mueller’s probe of Russian election interference.

Within several hours, news of a tentative deal to reopen the government for three weeks surfaced on Capitol Hill. Initial reports indicated that a continuing resolution to end the shutdown would include $1.3 billion for border security, giving Trump and his Democratic opponents time to negotiate over demands for a wall along the country’s southern border.  

Word of staffing shortages affecting air-traffic control came early on the 35th day of the longest government shutdown in U.S. history as air-traffic controllers and other federal employees missed their second straight paycheck. Following the temporary “ground stop”  at LaGuardia, the FAA reported major delays at Newark Liberty International Airport due to wind, as well as delays at Philadelphia International Airport. Atlanta’s Hartsfield-Jackson airport, the busiest in the world, saw an average departure delay exceeding an hour as of noon.  The FAA identified the cause of the staffing shortage as “a slight increase in sick leave at two facilities,” the centralized Air Route Traffic Control Centers at Leesburg, Virginia, and Jacksonville, Florida. The agency said that the staffing-induced delays at LaGuardia were averaging 86 minutes.

While “sickouts” by employees at the Transportation Security Administration had merely affected security-checkpoint wait times in recent weeks, a lack of controllers directly leads to flight delays and cancellations. Since the first missed paycheck on January 11, TSA absenteeism has run at two to three times the rate for the same period last year. Some airports have seen painfully long wait times for security checkpoints; lines in Detroit took as long as 78 minutes on Wednesday, and some passengers in Atlanta waited for nearly 90 minutes last week. However, as the agency has reported in daily updates, only a fraction of a percentage point of travelers have waited longer than 30 minutes, and at least 90 percent of passengers waited less than 15 minutes.

In contrast, more air-traffic controllers calling in sick has a direct and dramatic affect on U.S. air travel. “You can’t replace them easily, and they are not overstaffed,” the aviation consultant Michael Boyd told me Thursday. “The air-traffic-control system is very, very thin.”

The industry prides itself on safety and has established mechanisms to limit traffic in case of controller shortages, explains John Hansman, a licensed pilot and an FAA adviser who leads MIT’s International Center for Air Transportation. “We’re going to run it safe. So if you only have a certain amount of people (for air-traffic control and security screening), you’re going to end up with delays. You will see fairly shortly, if nothing is fixed, really significant security delays, at the scale we had in the months after September 11.” If the shortage of controllers grows critical, he adds, “They would shut down the system instead of letting it run dangerous.”

This all raises questions: How many air-traffic controllers are calling in sick? Have they joined the “sickout” among TSA screeners? Is this a coordinated action, or simply the accumulation of isolated decisions?

The second no-pay payday on Friday is a possible reason that controllers called in sick. Some might feel a need to pursue outside work to pay the bills while waiting for the shutdown to end; Congress and Trump already enacted a law guaranteeing back pay for federal workers, but expenses pile up in the interim. Earlier in the week,  I spoke with a controller who works at Chattanooga’s airport, who warned that the TSA sickout could conceivably spread. “You may start seeing that in air-traffic control,” says Jon Manley, who is a local representative for the National Air Traffic Controllers Association. The union’s national spokesman, Doug Church, did not immediately respond to calls or emails Friday morning.

Aviation experts say they don’t anticipate a coordinated sickout or strike. Partly that’s because controllers typically earn much more than TSA screeners; the median salary for fully trained controllers is $125,000, while the starting salary for a TSA officer can be as low as $25,000. That makes them more likely to have emergency savings to get through a shutdown. But two missed paychecks might cause more concerns about payments for everything from rent and mortgages to credit-card bills and college tuition.

The years of training required to work as an air-traffic controller also contribute to a greater sense of commitment. “They define government professionalism,” Boyd, the aviation consultant, said of controllers. “There would be some real reticence to do anything resembling a sickout.” But if a shortage did occur, he added, “it would slow down the whole system.”

James Simmons, an aviation professor at the Metropolitan State University of Denver who has studied the air-traffic-control system, says he doesn’t expect any coordinated action, because controllers remember the 1981 mass dismissal that followed a strike declared by the previous union. “Controllers that I knew and still know were very surprised when President Reagan fired them,” says Simmons, who’s also a licensed pilot. “So my suspicion is that, even this many years later, controllers would be afraid of a coordinated action.”

Short of a mass strike, shortages can still hamper air travel. Controllers would have to lengthen the distances between aircraft, slowing departures and arrivals to decrease the volume of flights, Simmons explains. “The system does have ways to accommodate controller shortages, and my prediction is that would be where the airlines and the traveling public start to feel the effects.” Hansman, the MIT aviation expert, shares that view: “This is likely to be a place where, if a solution isn’t found fairly soon, this will really be one of the key pain points that will significantly impact the general public.”

On Wednesday, the heads of the National Air Traffic Controllers Association, the Air Line Pilots Association, and the Association of Flight Attendants said in a statement that they had “a growing concern for the safety and security of our members, our airlines, and the traveling public due to the government shutdown … Staffing in our air traffic control facilities is already at a 30-year low and controllers are only able to maintain the system’s efficiency and capacity by working overtime, including 10-hour days and 6-day workweeks at many of our nation’s busiest facilities.”

Airline CEOs spoke out Thursday. “Everyone needs to be on notice and on guard that this shutdown could harm the economy and it could harm air travel,” said Southwest CEO Gary Kelly. JetBlue’s CEO, Robin Hayes, highlighted the significance of the second no-pay payday coming Friday: “We are close to a tipping point as employees are about to miss a second paycheck.”

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