WILMINGTON, Del. (AP) — Nevada-based discount airline aha! has stopped flying after its parent, ExpressJet Airlines, filed for bankruptcy protection and said it would sell its assets.

ExpressJet said it faced lower-than-expected revenue because demand for travel weakened with new COVID-19 variants. It also said it was burdened with high costs, particularly for jet fuel.

The Atlanta-area company filed Tuesday for protection in the federal bankruptcy court in Delaware.

Aha! flew to about a dozen cities on the West Coast from its base in Reno, Nevada. A message Tuesday on its website said the airline was unable to help stranded travelers make other travel arrangements, and that customers booked on future flights should contact their credit card company for refunds.

ExpressJet, based in the Atlanta area, was formed in 1986 from several small commuter airlines. For many years, it flew smaller planes as a regional carrier for Continental, JetBlue, American and United. In 2020, United Airlines removed its planes from ExpressJet, wiping out the company's revenue. ExpressJet reinvented itself in 2021 as a charter airline and operator of aha!, which stood for air, hotel and adventure.

In the filing, a company executive said ExpressJet ceased all operations, including charter flights, and laid off most of its employees and will return its planes to leasing companies.

According to the bankruptcy filing, ExpressJet is owned by ManaAir LLC, a joint venture of KAir Enterprises and MNBS Associates.

The largest debt listed in the filing is a $10 million unsecured claim by the U.S. Small Business Administration under the payroll protection program that the government launched to help businesses hurt by the pandemic. It owes another $3.9 million for a pandemic-relief loan made by the Treasury Department.

ExpressJet said it has 1,300 now-furloughed pilots. It plans to try to sell the operating certificate it received from federal regulators.