NEW YORK — Delta Air Lines says it will close its regional carrier Comair at the end of September as it switches more of its flying to bigger jets.

Operating regional carriers has become more expensive while customers have been demanding roomier planes. Comair operates a fleet of mostly 50-seat regional jets, which Delta doesn't want to fly anymore.

Delta, which is based in Atlanta, had about 500 of the 50-seaters in 2008 and plans to reduce that to 125 within two years. Most of that flying will be replaced by new 76-seat jets as well as the 117-seat Boeing 717s Delta is leasing from Southwest Airlines.

Comair represents only about 1 percent of Delta's flying, so the closure won't result in significant changes to Delta's network. Delta also said it won't result in fewer flights out of Comair's base at Cincinnati/Northern Kentucky International Airport. Besides Cincinnati, Comair also has hubs in Detroit and New York's JFK and LaGuardia airports.

Comair was founded in 1977. It started operating as Delta Connection in 1984. The regional airline had about 290 flights a day and 1,700 employees as of March, according to its website.

Before entering bankruptcy in September 2005, Comair had more than 7,000 employees and 1,160 flights.

Delta sold its other regional airlines — Compass and Mesaba — in 2010. Those carriers still run flights for Delta, as do several other companies.