on Monday said it expects revenue to fall in the second quarter after a decline in bookings following a deadly engine failure aboard one of its flights in April.

Southwest, which carries more travelers within the U.S. than any other airline, forecast a 3 percent drop compared with a year ago, in the revenue it generates per each seat it flies a mile, a key industry metric. The airline had warned of a 1 percent to 3 percent drop in operating revenue per available seat mile in April following the accident after it pulled marketing.

Southwest, a low-cost airline with peppy advertising campaigns, changed its website and tone after the April 17 accident. A fan blade broke off one of Southwest's Boeing 737's engines when a New York to Dallas flight was flying above 30,000 feet. Debris scattered, rupturing a window and partially sucking one passenger out of the opening. The plane made an emergency landing in Philadelphia. The passenger died.