As an added layer of safety, the Federal Aviation Administration (FAA) 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. 
 
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 5th. 
 
Read the Safety Alert for Operators (SAFO) regarding the Boeing 737-900ER here.

Source: FAA Jan. 21 statement
FAA advises the information is preliminary and subject to change.
 
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