The U.S. Department of Transportation said it fined United Airlines $1.1 million on Friday, the largest fine assessed for a tarmac-delay violation since the rule limiting long delays took effect in April 2010.
The airline was fined for tarmac delays that took place at Chicago-O'Hare International Airport on July 13, 2012, the DOT said.
The DOT rule says U.S. airlines operating domestic flights cannot let an aircraft stay on a tarmac for more than three hours without letting passengers deplane. Exceptions are allowed only for safety and if the pilot is advised by air traffic control that returning to the terminal would disrupt airport operations.
The DOT said the 13 tarmac delays exceeded the three-hour limit for the delays by two to 77 minutes for United and its United Express code-share affiliates. These delays were due to severe thunderstorms and lightning that caused several ramp closures and disrupted the movement of aircraft at O'Hare, the agency said.
The government agency said the airline will pay the United States $475,000. The remaining $625,000 will cover mitigation measures for affected passengers, and significant corrective actions by United to enhance future compliance with tarmac delay rules.
"It is unacceptable for passengers to be stranded in planes on the tarmac for hours on end," U.S. Transportation Secretary Anthony Foxx said in a statement.
United Continental, the parent of United Airlines, said it was "committed to complying with the tarmac delay regulations and we continue to improve our procedures while maintaining the safety of our customers and co-workers."
Although United had a contingency plan for tarmac delays, the airline did not implement the plan nor contact airport personnel or other airlines for assistance during the tarmac delays, the DOT said.