Two weeks after Airlines for America blamed the FAA for a lot of delays and canceled flights this summer, United Airlines jumped in.

Jon Roitman, United's chief operations officer, blamed the government agency and its oversight of an understaffed group of air traffic controllers for the problems.

Roitman wrote that the ATC staffing system can't handle more flights than the industry can. The US aviation system will be challenged until that is resolved.

More than half of its delay minutes and almost three-quarters of its cancellation since March were due to an understaffed FAA, according to United.

Travel Weekly reported that the FAA responded quickly.

The agency said that it was unfortunate that United Airlines had conflated weather-related air traffic control measures with ATC staffing issues. There are multiple factors that affect the system, including airline staffing levels, weather, high volume and ATC capacity, but the majority of delays and cancellation are not due to staffing at the FAA.

The FAA noted that while airlines have cut back their summer schedules and blamed it on a shortage of air traffic controllers, United still canceled more than 250 flights over two days during the Fourth of July holiday weekend.

The FAA said that they will hold airlines accountable while standing ready to collaborate so that Americans can expect safe, reliable and affordable service when buying an airline ticket.

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