Ten people on a Delta Air Lines flight were evaluated or treated by medical personnel after their plane was unable to pressurize above 10,000 feet after taking off from the Salt Lake City airport Sunday, Delta said.

Delta flight 1203, a Boeing 737-900, was bound for Portland with 140 passengers, but returned to Salt Lake City International Airport because of the pressurization issue. It landed at about 8:30 a.m. Mountain time, said the Federal Aviation Administration. The oxygen masks did not deploy, but medical personnel met the flight at the gate, Atlanta-based Delta said.

“We sincerely apologize to our customers for their experience on flight 1203 on Sept. 15,” Delta said in a written statement. “The flight crew followed procedures to return to SLC where our teams on the ground supported our customers with their immediate needs.”

The Boeing 737-900 is a different model than the 737 MAX 9 jets that temporarily were grounded earlier this year after part of the fuselage of an Alaska Airlines MAX 9 blew off during a flight. The MAX aircraft eventually were cleared to fly. Delta does not currently have any MAX aircraft in its fleet.

KSL-TV, a television station in Salt Lake City, reported on its website that one passenger who was on the flight said she felt a stabbing sensation in her ear. “I grabbed my ear, and I pulled my hand back and there was blood on it,” passenger Jaci Purser said, per KSL. Purser told the station she was diagnosed with a ruptured eardrum.

Another woman on the flight said she saw a passenger with a bloody nose, KSL reported.

Delta said the plane was taken out of service Sunday and returned to service Monday.

The FAA said it will investigate the incident.