With flight reductions beginning Friday at 40 major U.S. airports , Transportation Secretary Sean Duffy said safety is his top priority — but he declined to share information about the data that led to the decision to cut capacity.

Airlines were ordered to reduce flights as air traffic control staffing grew increasingly strained during the government shutdown , leading to intermittent ground stops.

"We had seen the rolling staffing triggers that come from air traffic controllers — one day it was L.A., another day it was in New York, Minneapolis, Atlanta — and so as we were looking at data, we were seeing increased numbers in some of the categories we don't like," Duffy told "CBS Mornings" on Friday.

He would not give specifics about what the data showed, but said it will be

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