WASHINGTON, D.C. — The Federal Aviation Administration is recommending that operators of Boeing 737-900ER aircraft visually inspect mid-exit door plugs to ensure the door is properly secured.

The Boeing 737-900ER is not part of the newer MAX fleet but has the same door plug design.

The FAA posted the statement on its site this past weekend, calling the extra measure “an added layer of safety.”

The FAA added that in accordance with their Safety Management Systems, operators conducted additional inspections on the Boeing 737-900ER following the loss of a mid-cabin door plug on a Boeing 737-9 MAX airplane on January 5.

That incident, on an Alaska Airlines flight taking off from Portland, OR, resulted in an emergency landing with all passengers and crew safe and sound. Alaska Airlines has put a flexible rebooking and change policy in place.

The FAA’s subsequent grounding of the B737-Max 9 fleet is still in effect. On Jan. 17 the FAA said that “after taking decisive action to ground 171 Boeing 737-9 MAX airplanes, the FAA is now investigating Boeing’s manufacturing practices and production lines, including those involving subcontractor Spirit AeroSystems, bolstering its oversight of Boeing, and examining potential system change.”