May 7 (Reuters) - Southwest Airlines Co on Tuesday said an important revenue measure fell in April as it faced softer demand and disruptions caused by furloughs of U.S. air traffic control staff.
Unit revenue, or passenger revenue per available seat mile, fell 4 percent to 5 percent from the year-earlier April, the U.S. carrier said.
Delta Air Lines Inc and US Airways Group Inc also reported unit revenue declines for April.
Staff furloughs at U.S. air traffic control towers last month caused flight delays at some airports. The furloughs, which lasted for about a week, were suspended after passage of a bill allowing the Federal Aviation Administration to shift money within its budget to stop them.
Southwest said traffic, measured in revenue passenger miles, rose 1.5 percent in April.