Ten weeks after American Airlines became the first commercial airliner to put the Boeing 737 MAX back in use, the carrier was forced to make an emergency landing with one of the planes on Friday.

American Flight 2555 from Miami to Newark-Liberty International Airport in New Jersey landed safely at Newark after declaring an emergency when the captain shut down one of the engines over a potential mechanical problem.

According to Reuters News Service , the possible issue was related to an engine oil pressure or volume indicator and not the result of anything related to the computer software system linked to two fatal 737 MAX crashes in 2018 and 2019 that prompted the plane’s 20-month grounding.

Boeing Co said it was aware of the American flight, and the Federal Aviation Administration (FAA) said it will investigate.

When it cleared the plane to fly again, FAA Administrator Steve Dickson said he was confident that the jet was safe but warned that in-flight mechanical problems occasionally occur with all commercial aircraft.

“For that reason, it is inevitable that at some time in the future, a Boeing 737 MAX will turn back to its originating airport, divert, or land at its destination with an actual or suspected in-flight problem,” he said. “It’s very important to differentiate between these routine events that happen with any aircraft and the acute safety issues that led to the loss of lives and grounding of the MAX.”

American began flying the MAX again in late December.