FAA recommends airlines inspect door plugs on another Boeing model

Weeks after a mid-cabin door plug fell off during the ascent of an Alaska Airlines Boeing 737 Max 9, the FAA is recommending flight operators check another model of Boeing airplanes.

On Sunday night, the FAA issued a statement recommending operators of the Boeing 737-900ER "visually inspect mid-exit door plugs to ensure the door is properly secured." In a statement late Sunday night, Boeing said it fully supports "the FAA and our customers in this action."

The 737-900ER has the same door plug design as the 737 Max 9.

According to the FAA’s safety alert, some operators that were conducting additional inspections on their 737-900ER mid-exit door plugs "noted findings with bolts during the maintenance inspections."

The FAA noted that the Boeing 737-900ER has over 11 million hours of operation and 3.9 million flight cycles, and the door plug has not been an issue. Major airlines that fly the Boeing 737-900ER include Alaska, Delta and United.

In a statement, United, which has 136 of the aircraft in its fleet, said it has “started proactive inspections" of its "Boeing 737-900ER aircraft earlier this week.” The company expects them to be concluded in the next few days. The airline said it expects no disruption to customers.

Alaska Airlines also issued a statement saying it began inspecting the 900 ER planes "several days ago."

"We have had no findings to date and expect to complete the remainder of our -900ER fleet without disruption to our operations," the statement read.

In its statement, Delta Airlines said, "we elected to take proactive measures to inspect our 737-900ER fleet. 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.”

This will impact 380 aircraft across the world, a source told ABC News.

Earlier this month, the door plug fell out of an Alaska Airlines Boeing 737-Max 9 after the plane took off for Ontario, California, after departing Portland.

Six crew members and 171 passengers were on board Flight 1282, the airline previously said.

The cabin became depressurized shortly after takeoff, and the pilots asked for an emergency landing, according to the transcript of an air traffic control call from LiveATC.net.

The door was found several days later. The NTSB is investigating the incident.