The airports can choose to pick up the cost to keep their towers open, but few are expected to be able to afford that.
Beyond the airfields, some mayors are concerned about the impact on tourism if tower closures lead to the loss of passenger service. And there are worries of other effects, including whether medical helicopter pilots might stop using airports without tower controllers.
Rep. Aaron Schock, an Illinois Republican whose district includes the Springfield airport, said the FAA's operational budget has grown about 40 percent over the past decade and there's no reason it can't operate safely under the automatic spending cuts, known as sequestration.
"Any action by the Obama administration that does jeopardize safety is more evidence that the White House is implementing the sequester in ways to only score political points," Schock said.
Robert Poole, an aviation expert at the Reason Foundation think tank, said the effect could be minimal for some small airports that have been overdeveloped as a result of politicians bringing money home from Washington.
In addition to round-the-clock tower closures, overnight shifts could be eliminated at 72 control facilities, including at much larger airports such as Midway, which sees an average of 50 flights daily between 10 p.m. and 7 a.m., nearly all of them passenger flights operated by carriers that include Southwest and Delta.
That raises the possibility that full-size jetliners could be landing there without any help from controllers.
Airlines have yet to say whether they will continue offering service to airports that lose tower staff.
"It's premature to discuss flight cancellations, as the earliest any furloughs would occur is April 7," said Katie Connell, spokeswoman for the industry group Airlines for America. "We are working with the FAA to minimize any impact to passengers and shippers."
Chicago pilot Robert McKenzie, who has a commercial license but primarily flies a small Cessna, has a lot of experience landing at smaller airports without control towers.
Doing so involves a lot more concentration, he said. Pilots have to watch for other aircraft, take note of weather conditions, look for debris on runways and make calls over the radio — all while operating their own plane.
Pilots have a very good track record of doing that safely. "But it never hurts to have somebody else out there helping you watch," McKenzie said. "It's a nice safety net to have."
McKenzie, a lawyer specializing in aviation matters, says the loss of towers is of concern to the Illinois Pilots Association, where he sits on the board of directors.
Most troubling, he said, would be the loss of towers at airports such as Springfield and Santa Fe, which are used by a mix of small private planes and larger passenger aircraft that often converge on airfields at different speeds and using different procedures. Controllers keep those planes safely separated and sequenced for landings.
Tower controllers also play a big role in keeping aircraft from taxiing across active runways, something that has been a key FAA focus for years.
"When you're at an uncontrolled field, avoiding that problem is entirely dependent on other pilots not making mistakes," McKenzie said. "There's nobody there as a backup."
Associated Press Writer Jeri Clausing contributed to this report from Albuquerque, N.M.
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