Delta Air Lines said overnight maintenance caused website and mobile application outages Thursday, preventing customers from using delta.com from booking flights.

For a total of five hours, customers were unable to go online to book flights or check departure and arrival schedules on delta.com or on mobile devices due to the server issues.

One episode in the morning lasted for four hours and another later in the day lasted for an hour, according to Delta spokesman Paul Skrbec.

“No flight delays were reported as a result of this issue and customers were able to check in using airport self-service kiosks throughout the entire event and book with directly with Delta Reservations,” Skrbec said.

In addition to urging customers to use kiosks at Hartsfield-Jackson International Airport and other airports, the carrier advised travelers to call its 1-800-221-1212 number to book or check on flights.