US investigating why Delta passengers remained on plane in extreme heat

"I want to know how it was possible for passengers to be left in triple-digit heat onboard an aircraft for that long," Buttigieg told Reuters on Thursday, calling the issue "infuriating" and "shocking."

During tarmac delays, airlines must provide comfortable cabin temperatures and begin moving the plane within three hours of a delayed domestic flight to a location where passengers can exit.

Delta said it is reviewing the incident and added that multiple passengers were seen by first responders, while a flight attendant and passenger were transported to a local hospital.

"Even under normal temperatures a tarmac delay is not supposed to go that long and we have rules about that, which we are actively enforcing and this is being investigated right now," Buttigieg said, adding there are also rules on maximum cabin temperatures.

A Fox News producer was onboard Flight 555 from Las Vegas to Atlanta that was ultimately canceled. Fox News reported passengers were waiting in 111 degree Fahrenheit (43.8 Celsius) heat with no air conditioning when the pilot announced the plane was returning to the gate citing multiple emergencies.

At that point passengers were then given a choice to leave the plane but were told if they did it could take days to get another flight to Atlanta, Fox News reported.

Delta said the time of initial departure until the flight was canceled was just over three hours, but the airline noted the plane did make at least one gate return due to heat-related weight and balance issues.

Delta said it apologized directly to passengers on the flight, adding they had received compensatory gestures and were accommodated on other flights.