The Federal Aviation Administration on Sunday recommended visual inspections of Boeing 737-900ER planes because of its 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 Airlines flight, but it uses the same door plug design, the FAA said.
There are 380 of the 737-900ER planes in service worldwide, a source familiar with the matter told NBC News. Boeing said in a statement on the inspections: "We fully support the FAA and our customers in this action."
There is no evidence that there are any problems or defects with the 737-900ER's mid-exit door plugs, the FAA noted. The model has logged 11 million hours of operation, according to the agency.
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 said it began inspecting its Boeing 737-900ER aircraft "several days ago" out of "an abundance of caution."
"We have had no findings to date and expect to complete the remainder of our -900ER fleet without disruption to our operations," the airline said.
United Airlines said Monday that it started inspections of its 136 Boeing 737-900ER aircraft earlier this week as well and expect to finish "in the next few days without disruption to customers."
Delta Air Lines said it too is inspecting its fleet, adding, “We’re in full compliance with regulation from federal authorities regarding the safety of our aircraft, and at this time we do not anticipate any operational impact.”
Alaska Airlines and United Airlines inspections of 737 Max 9 planes in the wake of the Jan. 5 incident 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 it’s possible the fasteners were lost when the so-called door plug was expelled.
The near-capacity Alaska Airlines 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."