The U.S. Federal Aviation Administration on Sunday recommended visual inspections of Boeing 737-900ER planes because the have similarities to the model involved in a Jan. 5 midair emergency on an Alaska Airlines flight.

The inspections should focus on “mid-exit door plugs,” the FAA said in a statement, referring to the same type of panel that detached from Alaska Airlines flight 1282.

The Boeing 737-900ER is used by Alaska, Delta and a number of overseas airlines. It is older than the 737 Max 9 involved in the Alaska flight, but it uses the same door plug design, FAA said.

There is no evidence that there are any problems or defects with the 737-900ER’s mid-exit door plugs, the agency noted. The model has logged 11 million hours of operation, according to the FAA.

Operators had already conducted additional inspections of the 737-900ER following the Alaska Airlines emergency, the agency said. Sunday’s announcement said operators need to ensure the door plugs are properly secured as “an added layer of safety.”

Alaska Airlines and United Airlines inspections of 737 Max 9 planes in the wake of the Jan. 5 accident found some aircraft with door plugs that contained bolts that were not tightened to specified torque levels.

National Transportation Safety Board officials said an examination of a panel that blew out of the Alaska Airlines flight showed signs of fractured guides and missing bolts, though cause was still under investigation.

The near-capacity Alaska flight was en route to Ontario, California, from Portland, Oregon, when the door detached in an explosive moment of decompression. No serious injuries were reported, but officials said the situation could have been much worse.

The next day, the FAA issued an emergency airworthiness directive that ordered an estimated 171 737 Max 9s grounded pending inspections and subsequent approval to fly.

“The FAA has launched an investigation, increased its oversight of Boeing and continues to evaluate inspection and maintenance data from the initial 40 inspections of the MAX-9 aircraft,” the FAA said Sunday night.

It added, “The Boeing MAX-9 aircraft will remain grounded until the FAA is satisfied they are safe to return to service.”