Over the weekend, Delta Airlines temporarily grounded all domestic flights due to an unexplained technical error, the second major American airline to do so in the last seven days.
"Delta teams are expeditiously working to fix a systems outage that has resulted in departure delays and cancellations," said Delta after lifting the ground halt (which the FAA attributed to "automation issues") Sunday evening. "Flights in the air remain unaffected."
Last weekend, United Airlines similarly stopped all domestic flights over what it called "an IT issue." The grounding was finally lifted two hours later.
Once unheard of, IT-related ground halts have become troublingly frequent over the past six months. From CNN:
In September, British Airways suffered a computer problem that caused delays and long lines at airports in the United States and Europe.
In August, Delta was forced to cancel around 2,000 flights after a major system failure. That came only a few weeks after an outage caused more than 1,000 cancellations at Southwest Airlines.
Other than denying being hacked, the airlines generally haven't disclosed the exact nature of the errors. In July, however, Southwest CEO Gary Kelly described his company's glitch as a "once-in-a-thousand-year flood" caused by single rogue router that tied up hundreds of software applications.
"In 45 years, we've never had a challenge like this one," Kelly told The Dallas Morning News. "This isn't a drill you can run."
As they come to rely on increasingly complex automated systems, airlines might consider what kind of drills they can run.