The closures will not force the shutdown of any of those airports, but pilots will be left to coordinate takeoffs and landings among themselves over a shared radio frequency with no help from ground controllers. All pilots are trained to fly using those procedures.

The plan has raised concerns since a preliminary list of facilities was released a month ago. Those worries include the impact on safety and the potential financial effect on communities that rely on airports to help attract businesses and tourists.

“We will work with the airports and the operators to ensure the procedures are in place to maintain the high level of safety at non-towered airports,” FAA Administrator Michael Huerta said in a statement.

The FAA is being forced to trim $637 million for the rest of the fiscal year that ends Sept. 30. The agency said it had no choice but to subject most of its 47,000 employees, including tower controllers, to periodic furloughs and to close air traffic facilities at small airports with lighter traffic. The changes are part of the across-the-board spending cuts known as sequestration, which went into effect March 1.

The airports targeted for tower shutdowns have fewer than 150,000 total flight operations per year. Of those, fewer than 10,000 are commercial flights by passenger airlines.

Airport directors, pilots and others in the aviation sector have argued that stripping away an extra layer of safety during the most critical stages of flight will elevate risks and at the very least slow years of progress that made the U.S. aviation network the safest in the world.

Airlines have yet to say whether they will continue offering service to airports that lose tower staff.

The 149 air traffic facilities slated to begin closing on April 7 are all staffed by contract employees who are not FAA staffers. There were 65 other facilities staffed by FAA employees on the preliminary list of towers that could be closed. A final decision on their closure will require further review, the FAA said.

The agency is also still considering eliminating overnight shifts at 72 air traffic facilities, including some at major airports like Chicago’s Midway International and General Mitchell Airport in Milwaukee. There was no word Friday on when a decision will come.

Hundreds of small airports around the country routinely operate without controllers. Pilots are trained to watch for other aircraft and announce their position over the radio during approaches, landings and takeoffs.

But the overall air system’s safety is built on redundancy, and taking away the controller’s extra set of eyes is like removing stop signs or traffic lights from city intersections and forcing drivers to be more vigilant and cautious, says Paul Rinaldi, president of the National Air Traffic Controllers Association.

“That’s what the pilot is going to have to do now,” said Rinaldi, whose group represents nearly 15,000 FAA-employed controllers as well as some staff at privately run contract towers that were the subject of Friday’s announcement.

“A pilot is now going to have that extra duty of making sure that everybody seems to be doing the right thing on a crowded” frequency, he said.

And pilots will have to do that on top of flying the airplane or maneuvering it on the ground, “which is not an easy thing to do,” Rinaldi added. “It’s not like driving a car.”

Some aviation experts say the elimination of overnight shifts should have been carried out regardless of the sequester at facilities that don’t see enough traffic to justify the expense of staffing towers.

The budget cuts being forced on the FAA could provide the agency with political cover to make some of those changes.

“There’s a tendency over time to have Congress direct more money to small airports than would probably be economically justified,” explained Robert Poole, an aviation analyst at the Reason Foundation think tank.

He said his own initial review of the list released Friday showed that many of the towers that will close around the clock are at airports with few or no scheduled passenger flights, indicating that Friday’s decision would likely have little effect on airline service.

Hoping to escape the final cut, airport directors were left to argue with the FAA about whether the closure of their facilities would adversely affect what the agency described in a letter as the “national interest.”

After reviewing those responses, the FAA decided to keep open 24 towers, including one at the Kissimmee Gateway airport serving Orlando, Fla., and the Denver area’s Front Range airport.

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FAA statement on tower closures with list of affected airports:www.faa.gov/news/press_releases/news_story.cfm?newsId=14414