Delta Air Lines is shutting down its regional subsidiary Comair, marking a shift away from small regional jets and changing dynamics in the airline industry.

Comair is one of Delta Connection's regional feeder carriers and operates about 235 flights a day to 73 cities, with a significant presence in Cincinnati. Comair flights make up about 1 percent of Delta's flight capacity, according to Delta.

Atlanta-based Delta said Comair will cease operations Sept. 29 but passengers will not be affected. Other Delta Connection partners will operate any Delta Connection flights scheduled to be flown by Comair after that date.

Delta will retire Comair's 16 50-seat regional jets. It will lease the other 28 regional jets in Comair's fleet to other Delta Connection carriers, according to Delta spokeswoman Kristin Baur.

Comair is based in Erlanger, Ky., near Cincinnati.

The company's roughly 1,700 employees will be laid off, including about 30 Georgia-based based pilots and flight attendants, according to Baur. Non-union employees will get severance and job placement help, and the company will negotiate with unions representing the roughly 800 pilots, 450 flight attendants and 225 mechanics on separation benefits.

On the Comair flight attendants union website, a union leader posted a note on the Delta decision, adding, "My heart is broken; I grieve with each of you."

Delta had put Comair up for sale years ago, finding no buyers. Comair operates flights in the Midwest and East Coast, including Cincinnati, New York, Detroit, Memphis, Washington, D.C. and Atlanta.

Founded in Cincinnati in 1977, Comair became a Delta Connection carrier in 1984, with Delta soon after taking a partial ownership share. The carrier was a financial star of the burgeoning regional industry and in the 1990s became a launch customer for the 50-passenger Canadair regional jet. Comair gradually expanded at the Cincinnati airport.

Delta acquired all of Comair for about $2 billion in 2000, in a move to absorb its profits and gain full control of its regional jet fleet.

A tragic chapter in Comair's history came in 2006, when a Comair flight crashed while attempting to take off from the wrong runway at Blue Grass Airport in Lexington, killing 49 people.

Meanwhile, 50-seat jets were becoming economically less attractive to airlines and disliked by passengers in favor of newer, larger jets that are more fuel-efficient and less cramped. Delta Connection once used about 500 of the 50-seat regional jets but has begun retiring them in recent years.

Amid that backdrop and economy-related flight cuts, Comair had been gradually shrinking along with the Cincinnati hub. The hub once had more than 600 daily departures and now has about 120.

Comair operates some of the oldest 50-seat regional jets in the Delta Connection fleet, according to a memo from Comair president Ryan Gumm to employees. He called the decision to cease operations "an unfortunate necessity due to the economic limitations of our aging aircraft, cost structure, the long-term outlook for 50-seat aircraft, and our challenging industry and economy."

The decision comes as Delta plans to reduce its fleet of 50-seat regional jets from nearly 350 today to 125, enabled by a recently approved pilot labor contract and a deal to lease from rival Southwest Airlines all of the Boeing 717s Southwest inherited through its acquisition of AirTran Airways.