Delta's website and mobile app go down ATLANTA The website for Delta Air Lines Inc. (DAL) encountered a glitch Thursday, preventing passengers from checking in for flights or booking new tickets there. Delta's mobile app was down, too. Visitors to Delta.com got the following error message: The airline says the problems began before 11 a.m. Eastern time and that it was working to resolve the problem. By 2:40 p.m. ET, both the site and the app appeared to be up and running again. A spokesman says airport kiosks worked during the outage and that customers could book tickets by phone.