The Federal Aviation Administration said Saturday it will temporarily ground some Boeing 737 Max 9 airplanes used by U.S. airlines after a panel appeared to have detached from an Alaska Airlines flight midair.

The FAA said it will also ground 737 Max 9 planes that operate in U.S. territory. In total, the order will affect about 171 of the airplanes out of 218 worldwide, the FAA said.

“The FAA is requiring immediate inspections of certain Boeing 737 Max 9 planes before they can return to flight,” FAA Administrator Mike Whitaker said. “Safety will continue to drive our decision-making as we assist the [National Transportation Safety Board’s] investigation into Alaska Airlines Flight 1282.”

No serious injuries were reported on the flight, which turned back and landed safely at Portland International Airport on Friday evening.