(NEXSTAR) – Southwest Airlines is celebrating its 50th anniversary by giving customers 50% off fall flights.

The flight must be booked by Thursday, June 17, for travel from Sept. 15 to Nov. 3. The sale started on Tuesday.

Travelers must use the promo code SAVE50 to get the discount, which is applied before taxes and fees.

All destinations in Southwest’s network are eligible for the promotion, including international ones.

All Southwest Airlines flights come with two free checked bags and free drinks, and the airline doesn’t charge any cancellation or change fees.

The flight sale is happening as the airline attempted to recover Wednesday from technology problems that started earlier this week. Passengers had to deal with canceled flights and delays for a third day.

By late afternoon Central time, Southwest had canceled nearly 400 flights and more than 1,000 were delayed, according to tracking service FlightAware. Combined, the disruptions affected 40% of the airline’s schedule.

The Federal Aviation Administration had issued a nationwide ground stop on Tuesday for all Southwest flights at the company’s request as they tried to resolve the system problems.

The Associated Press contributed to this report.