Federal officials are investigating a Delta flight that taxied around Las Vegas airport for nearly 90 minutes in triple-digit temperatures on Monday, with at least one person requiring medical attention.

“The reports are shocking and we are investigating,” Transportation Secretary Pete Buttigieg said in an interview with Reuters, a Department of Transportation official confirmed to CNN.

“I want to know why passengers were allowed to be left in triple-digit heat for so long on board,” he said.

“We hold airlines accountable for violations,” an official told CNN.

Federal regulations stipulate that major U.S. airlines must allow passengers to disembark if domestic flights are delayed for more than three hours. For international flights, the threshold is 4 hours. If the delay lasts longer than 2 hours, the airline must provide snacks and water.

Delta said it was aware of the investigation and was cooperating.

The airline apologized for the incident and said at least one person needed medical attention “due to heat discomfort”.

They are also “investigating the circumstances that resulted in uncomfortable temperatures on board.”

According to flight tracking website FlightRadar24, the Boeing 757 left the gates of Las Vegas on Monday afternoon but never left the ground. The plane taxied to the end of the runway, then turned around and returned to the terminal.

The loop took at least 86 minutes, according to FlightRadar24 data.

Airlines can face hefty fines for violating delay rules. In 2019, Delta was fined $750,000 for 11 non-compliant flights. The airline was recognized as part of the fine for spending $450,000 on customer compensation and technology and process upgrades.

For more CNN news and newsletters, create an account at CNN.com