- The FAA told airlines to inspect the door plugs of another Boeing jet, the 737-900ER.
- It uses the same door-plug design as the 737 Max 9 involved in the Alaska Airlines blowout.
A second plane has been dragged into the Boeing 737 Max 9 saga as the Federal Aviation Administration recommended a new set of inspections on Sunday.
The Boeing 737-900ER uses the same door-plug design as the Max 9, which has come under scrutiny since the Alaska Airlines blowout on January 5.
The Max 9 remains grounded as airlines continue inspections, although the 737-900ER isn't grounded.
On Sunday, the FAA said it recommends "operators of Boeing 737-900ER aircraft visually inspect mid-exit door plugs to ensure the door is properly secured."
After the Alaska Airlines Flight 1282 door plug was recovered earlier this month, investigators found four bolts attached to the Max 9 were missing. The door plug is undergoing testing to determine if they were ever installed.
Loose hardware was also discovered on other Max 9 jets after they were grounded, by United and Alaska Airlines.
The FAA's safety alert also notes that during maintenance inspections, some operators have "noted findings with bolts" on the 737-900ER.
The 737-900ER is the third generation of Boeing's narrowbody 737 jet, which was first delivered in 2007. It doesn't appear to have been involved in any door-plug incidents like the Max 9.
The fact that the FAA is issuing a safety alert based on Boeing's design suggests more unease around the American manufacturer.
According to Reuters, the vast majority of 737-900ER jets with a door plug are operated by three US carriers: United, Alaska, and Delta Air Lines.
United and Alaska told Reuters they have begun the inspections and expect them to be completed soon without disruption.
Delta Air Lines said it had "elected to take proactive measures to inspect our 737-900ER fleet" and doesn't anticipate an impact on its operations.