The top air safety regulator said on Thursday his agency expects airports will handle fewer flights during peak hours this summer because of furloughs at control towers.
However, airlines have not told the agency this will mean fewer overall flights or less revenue for them, Federal Aviation Administration chief Michael Huerta said.
Airlines are still trying to understand the impact of furloughs among air traffic controllers, Huerta told reporters.
The FAA plans to cut control-tower staffing by 10 percent at Atlanta, Chicago, Los Angeles and other busy airports starting on Sunday because of mandatory budget reductions required under so-called sequestration.
Huerta, speaking after a Senate hearing, said the FAA is in regular conversation with airlines in an effort to understand what the effect of the furloughs will be.
He said FAA "modeling" of the potential effects is specific to individual airports. But in general, "if we have reduced controller hours, what we would expect to see is during peak periods a reduction of arrival rates", he said.
"So one of the things we're trying to understand is how that impacts the system overall," he said, without elaborating.
His remarks were the clearest statement yet of the potential effect on airports and airlines. He has previously said that "if sequestration means fewer flights can be safely accommodated in the (national air space), then there will be fewer flights".
Air-traffic controller staffing has drawn attention in recent weeks after the FAA said it would close control towers at 149 small airports across the country, starting on June 15. Congress has asked for safety studies of those plans, but the FAA has so far not provided them.
In a sharp exchange during the hearing, Senator Jerry Moran, a Kansas Republican, asked Huerta for copies of the studies that were conducted on each of the 149 airports.
Last month, Representative Bill Shuster, a Pennsylvania Republican, and Senator John Thune, a Republican from South Dakota, asked Transportation Secretary Ray LaHood for studies the FAA conducted to determine that closing the smaller towers was safe.
Last week, a larger group of lawmakers told Huerta and LaHood that they opposed the planned closures, and said the FAA had not determined the effect of the move on safety or airport operations.
"It is deeply troubling that the agency seems intent on proceeding with the closure of key air traffic control assets absent adequate safety data and study," they said in a letter to LaHood and Huerta.
Huerta has said all but one of the towers slated for closure already shut for significant parts of the day, and have procedures for flights to land without an air traffic controller on duty. The FAA chose airports that handle fewer than 150,000 flights a year and fewer than 10,000 commercial flights a year.
The furlough issue, which is separate from the closures, could potentially have a larger impact since it affects 47,000 air traffic controllers in facilities that guide flights into and out of busy hubs and across the nation's airspace.
The furloughs are expected to save $200 million in the current fiscal year, which ends in September, while the tower closures are expected to save $25 million, Huerta said. The agency is required to cut $637 million from its nearly $16 billion budget for the current fiscal year.
(Reporting by Doug Palmer and Alwyn Scott; Editing by Maureen Bavdek and Dale Hudson)