SAFO 73790: Boeing 737-900ER Mid-Cabin Door Plug Inspection.

Distributed by: Flight Standards

SAFOSafety Alert for Operators

U.S. Department

of Transportation

Federal Aviation

Administration

SAFO 24001

DATE: 01/21/24

Flight Standards Service

Washington, DC

http://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo A SAFO contains important safety information and may include recommended action. Besides the specific action recommended in a SAFO, an alternative action may be as effective in addressing the safety issue named in the SAFO. The contents of this document do not have the force and effect of law and are not meant to bind the public in any way. This document is intended only to provide clarity to the public regarding existing requirements under the law or agency policies.

Subject: Boeing 737-900ER Mid-Cabin Door Plug Inspection.

Purpose: This SAFO informs aircraft operators under Title 14 of the Code of Federal Regulations (14 CFR) Parts 91, 91 subpart K (Part 91K), 121, 125, 129, and 135 about information pertaining to the Boeing 737-900ER fuselage plug assembly. This SAFO also recommends that operators perform key portions of the Boeing 737-900ER Fuselage Plug Assembly Maintenance Planning Document (MPD) Inspection Tasks, related to the 4 locations where a bolt/nut/pin installation is used to secure the door to the airframe, as soon as possible. This information is applicable to all operators under 14 CFR that operate the Boeing 737-900ER aircraft.

The Federal Aviation Administration (FAA) continues to evaluate data involving the mid-cabin door plug and will determine additional action as necessary.

Background: Following the in-flight loss of a mid-cabin door plug on a Boeing 737-9 MAX airplane, on January 5, 2024, the FAA began collecting data on the incident airplane and related airplanes to scope the applicability of any action to mitigate risk to the fleet. On January 6, 2024, the FAA determined an unsafe condition existed with the Boeing 737-9 MAX and an Emergency Airworthiness Directive (EAD) was warranted.

On January 6, 2024, the FAA issued an EAD (AD number 2024-02-51) to address the potential in-flight loss of a mid-cabin door plug on Boeing 737-9 airplanes. The FAA also issued a Continued Airworthiness Notification International Community (CANIC) providing notice of pending significant safety action.

Discussion: The Boeing 737-900ER mid-exit door plugs have an identical door plug design to the 737-9 MAX. As part of their Safety Management Systems, some operators have conducted additional inspections on the 737-900ER mid-exit door plugs and have noted findings with bolts during the maintenance inspections.

Recommended Action: Operators are encouraged to conduct a visual inspection to ensure the door plug is restrained from any movements through the two (2) upper guide track bolts and two (2) lower arrestor bolts. Please refer to the Aircraft Maintenance Manual and 737-900ER Fuselage Plug Assembly Maintenance Planning Document (MPD) for more information, regardless of if this inspection has been conducted under the existing maintenance program prior to the EAD. As Operators conduct the visual

Distributed by: Flight Standards

inspections, they are also encouraged to report findings to their certificate management office.

Contact: Questions or comments regarding this SAFO should be directed to the Aircraft Maintenance Division via email at 9-AWA-AFS-300-Correspondence@faa.gov, or via telephone at (202) 267-1675.