(NEXSTAR) – The Federal Aviation Administration had instructed airlines to cut back on their flight schedules during the last weeks of the government shutdown, resulting in cancelations and delays at some of the country’s biggest airports. The end of the shutdown means airlines can begin working to resume normal operations as soon as Transportation Secretary Sean Duffy and the FAA give the go-ahead. But as it currently stands, the federal government has maintained its directive for airlines to cut flights by 6%, even after the shutdown has officially come to an end. A timeline for resuming normal operations, therefore, has yet to be specified by America’s major carriers. Delta CEO Ed Bastian was perhaps the most optimistic, saying Thursday on “CBS Mornings” that air travel should “return to normal by the weekend.” He seemingly came to this conclusion based on an assumption that air traffic controllers would be returning to work once they get their paychecks “in the next day or so.” Staffing in the control towers is indeed returning to normal (or close to normal) levels, according to the FAA. Last Saturday, the staff shortages peaked when 81 different FAA facilities warned they were running low on workers, but on Thursday morning, the FAA didn’t list any staffing warnings at airports and other radar facilities across the country. Still, some experts are wary that air travel will return to normal right away. Chris Sununu, the former governor of New Hampshire and current president and CEO of Airlines for America, had said Wednesday that airlines “cannot flip a switch and resume normal operations immediately after a vote — there will be residual effects for days.” The air travel trade association later released a statement to the Associated Press saying it was “eager to resume normal operations over the next few days once the FAA gives clearance.” But when asked Friday, Airlines for America reiterated its eagerness to resume full schedules, but omitted any timeline for doing so. “Fortunately, ATC staffing levels have been showing very positive signs of improving significantly, and we are eager to resume normal operations once the FAA gives clearance,” a representative for the association wrote in an emailed statement to Nexstar. Spokespeople for American Airlines and Southwest Airlines, meanwhile, suggested that both carriers would be ready to resume full flight operations before the holiday travel period, but did not indicate any hard-and-fast date for resuming operations. “We are encouraged by the signs of stability in the air traffic system, and we remain in close contact with the FAA as the agency does its work,” a Southwest spokesperson said. Even if the FAA drops its mandate to cut flights, certain aviation groups continue to warn that problems that predated the shutdown — especially those with air traffic controllers — could easily persist once the government is back up and running. In an open letter to Congress from the Modern Skies Coalition — which consists of the Air Line Pilots Association, Airlines for America, the Aerospace Industries Association and dozens more — the group suggested that the shutdown may have even exacerbated problems at the nation’s air traffic control towers. “Even before the shutdown, there was widespread recognition that we were dealing with an ailing air traffic control system,” reads the letter. “Congress recently made a significant downpayment on modernizing the FAA’s antiquated air traffic control system and the Department of Transportation (DOT) has prioritized ‘supercharging’ hiring to get air traffic control facilities fully staffed. But those initiatives are challenged as the shutdown continues. “As Transportation Secretary Sean Duffy has championed, we need much, much more for air traffic investment in this country. The shutdown takes all of that in the wrong direction.” A representative for the FAA did not immediately respond to a request for additional information on reducing flight cuts when contacted on Friday. Transportation Secretary Sean Duffy has previously said the decision will be based on the safety data that experts at the FAA are watching closely. The Associated Press contributed to this report.