United Airlines resumed operations last night (Sunday) after a computer problem temporarily grounded all domestic mainline flights.
Earlier, United says the flights were grounded due to an IT issue.
The flights were grounded due to a problem with the communication system that airplanes use to send information to United operations. Aircraft Communications Addressing and Reporting System, or ACARS, is used to record and transmit a range of information, including departure times, as well as weight and balance, which is used to calculate takeoff speeds.
The system outage was an issue for planes that had yet to depart, as pilots need this information to safely take off.
Planes already in the air were in no danger.
