United Airlines has said that all US domestic flights were suspended on Sunday because of a computer problem.
United Airlines spokesperson Maddie King blamed the ground stop on an IT issue, but did not give any further details.
CNN cited sources that said flights were grounded due to an error in the Aircraft Communications Addressing and Reporting System (ACARS), which is used by areoplanes to send information to United Airlines operations.
The issue has since been resolved, the airline announced via Twitter, and grounded flights were subsequently being cleared for departure. The airline is also offering travel waivers to customers affected by the IT issue.
Last October, United Airlines encountered a similar problem with its computer system that delayed flights for several hours.
A month prior, British Airways passengers experienced severe disruption and delays across airports worldwide, due to an IT glitch that had taken down the airlines check-in systems. Check-in procedures were reduced to hand-written records and passengers were reportedly issued hand-written boarding passes.
Also last year, Southwest's systems stumbled after a faulty router, which led to the cancellation of about 2,300 flights, while United Continental grounded flights over a bad router in June and July.
Delta Airlines had flights grounded in August due to a power outage that impacted Delta computer systems and operations worldwide, resulting in flight delays. The airline said its IT team was "working on some network issues that are impacting several applications, including our website".
A network connectivity issue was also to blame for check-in and baggage system issues at Melbourne Airport in November that led to delays. Sydney and Brisbane airports had previously been affected by an outage that left passengers unable to use the SmartGates at passport control.
In 2015, United Airlines launched a bug bounty program in response to the rising threat of cyber attackers. Researcher Randy Westergren said he had identified a serious vulnerability in an API endpoint that exposed Rewards members personal information, which took the airline around six months to fix.
The airline later awarded one researcher 1 million air miles for reporting the existence of a severe remote code execution (RCE) flaw.