If you’re flying on Southwest Airlines out of BWI Thurgood Marshall or any airport Monday morning, you may want to check your flight status before you leave the house.

Southwest Airlines passengers experienced a bit of travel trouble, when the airline delayed hundreds of flights Sunday and overnight. The airline blamed a computer glitch for the problem.

Southwest officials said they are using back-up systems to check-in travelers. Some terminals even had to issue hand-written tickets.

Representatives for Southwest say there is no indication that the problems were the result of hacking, but didn’t say what caused the problem or how long it would take to fix it.

The problem has affected the air carrier’s website, mobile app, phone centers and airport check-in systems.

Southwest has been forced to check in some customers manually and that has caused very long lines.

On Sunday, 450 of the airline’s 3,600 flights were delayed. Conditions at BWI Marshall were described as relatively routine.

“We understand that Southwest Airlines continues working to correct its technical malfunction,” BWI Marshall spokesman Jonathan Dean said. 

Most of Southwest’s flights are expected to depart on time Monday, but in a statement, Southwest requested that customers arrive at least two hours prior to their scheduled departures to help minimize delays.

They are also asking that passengers print boarding passes before coming to the airport.