[Mike Scott]

CHICAGO, Illinois (CNN) -- ATA Airlines has ceased all flights as it files for bankruptcy, apologizing to its customers for the airline's "sudden shutdown," according to a company statement released Thursday.

The low-cost, charter airline based in Indianapolis, Indiana, filed for Chapter 11 status on Wednesday as a result of financial problems "following the loss of a key contract for our military charter business," ATA said.

"Unfortunately, we were not in a position to provide our customers or others with advance notice," ATA said.

The airline, founded in 1973, served major business centers - including Chicago, Dallas and Oakland - and popular vacation spots throughout the United States, including Hawaii, Los Angeles, Phoenix, and Las Vegas. The airline also operated as a leading carrier for the U.S. military.

It operated 29 aircraft, including Boeing 737-800s, Boeing 757-200s, Boeing 757-300s, DC10s and Lockheed L-1011s.

At the time of its shutdown, ATA employed approximately 2,230 people, including approximately 600 pilots, more than 800 flight attendants, and more than 100 mechanics.