A Delta Air Lines flight taxied around the Las Vegas airport for nearly 90 minutes in triple-digit temperatures, causing at least one person to need medical treatment. The Boeing 757 aircraft left its gate at the LAS on Monday afternoon but never left the ground. The plane taxied to the end of a runway and then turned around and returned to the terminal.

“The reports are shocking and we are investigating,” said Transportation Secretary Pete Buttigieg, who spoke in an interview with Reuters.

“I want to know how it was possible for passengers to be left in triple-digit heat onboard an aircraft for that long.”

CNN reported that the transportation department “will hold the airline accountable for any violations,” including of rules around how long airplanes may sit on the ground with passengers aboard.

Federal rules say the major US airlines must allow passengers to deplane if a delay lasts three hours or more for domestic flights, four hours for international flights. Snacks and water must be provided if the delay lasts longer than two hours.

Delta said it is aware of and cooperating with the investigation. It apologized for the incident and said at least one person required medical attention “for heat-related discomfort.”

They are also “looking into the circumstances that led to uncomfortable temperatures inside the cabin.

Airlines can face significant fines for violations of the delay regulations.