The Federal Aviation Administration recommended late Sunday night that airlines begin visual inspections of door plugs installed on Boeing 737-900ER planes, the second Boeing model to come under scrutiny this month.
The F.A.A. said the plane had the same door plug design as the company’s newer 737 Max 9. The agency grounded about 170 Max 9 jets after a door panel blew off one of the planes shortly after an Alaska Airlines flight left Portland, Ore., on Jan. 5, forcing an emergency landing.
The door plugs are placed as a panel where an emergency door would otherwise be if a plane was configured with more seats.
After grounding the Max 9 planes, the F.A.A. subsequently announced it was investigating whether Boeing failed to ensure that the jet was safe and conformed to the design approved by the agency.
The F.A.A. said on Sunday that the door plug on the 737-900ER, an earlier-generation model that is not part of Boeing’s Max line, had not yet been a problem.
“As an added layer of safety, 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 agency said in a statement.
The F.A.A. is recommending that the airlines using the 737-900ER immediately inspect the four locations used to secure the door plug to the airframe. The 737-900ER has over 11 million hours of operation and about four million flight cycles, according to the F.A.A. Boeing delivered about 500 of the planes globally between 2007 and 2019, though not all of them have door plugs.
“We fully support the F.A.A. and our customers in this action,” Boeing said in a statement.
Alaska Airlines and United Airlines, which both use the 737-900ER, said in statements that they had already started inspecting their planes of that model. Delta Air Lines, which also flies the aircraft, said it had “elected to take proactive measures to inspect our 737-900ER fleet.” None of the airlines expected any disruptions to their operations.
The episode involving the Alaska Airlines 737 Max 9 flight this month did not result in any serious injuries, but it could have been far more serious if the plane had been at its cruising altitude. The National Transportation Safety Board is investigating the episode in hopes of learning what caused the door plug to blow off the plane.
In the meantime, the F.A.A. recently ordered an initial round of inspections of 40 of the grounded Max 9 planes as it works to finalize inspection instructions for the aircraft. The agency announced last week that those inspections had been completed and that it would review the data from them.
