The National Transportation Safety Board (NTSB) has issued its final report on the Alaska Airlines Boeing 737-9 that lost a door plug shortly after takeoff out of Portland, Oregon, in January 2024.
The 158-page report includes several pages of recommendations for improving manufacturing processes and safety culture at Boeing.
What Happened
The aircraft experienced rapid depressurization as it climbed through 14,830 feet and the door plug tore from the airframe. The flight crew declared an emergency, and the Boeing 737-9 returned to Portland International Airport.
There were no deaths or serious injuries among the 171 passengers and six crew members, and Alaska Airlines grounded its 737-9 fleet out of an abundance of caution.
This was followed by months of painstaking inquiry into operations at the airline, the FAA, and Boeing. It was determined that the door plug had been removed to correct some rivet deficiencies on the fuselage and then reinstalled without the required retaining bolts or the paperwork to track the repair and replacement.
Per the NTSB final report, the investigation determined that the probable cause of the accident was the “in-flight separation of the left Mid Exit Door plug (MED) plug due to Boeing’s failure to provide adequate training, guidance, and oversight necessary to ensure that manufacturing personnel could consistently and correctly comply with its parts removal process.”
Other issues raised were the alleged lack of adequate employee training and oversight by both Boeing and the FAA and the lack of child restraint systems for children under the age of two years old.
Present FAA regulations allow children under the age of two to be seated on the lap of an adult in an aircraft without an additional restraint system. The cabin depressurization after the door plug failure caused unsecured objects such as phones, toys, and clothing to be violently ejected, and concerns were raised at an NTSB hearing in June that young children were similarly at risk barring additional security measures or a regulation change.
Recommendations for Boeing
The board had a long list of recommendations for Boeing. Among them is to have newly manufactured aircraft be equipped with a redesigned door plug and aircraft already in service be retrofitted with it once the design is certified.
Other recommendations for Boeing:
- Apply an updated safety risk management process to current and future revisions to parts removal procedures to ensure they provide clear and concise guidance for determining when a removal record is needed.
- Develop recurrent training on parts removal for Boeing manufacturing personnel that emphasizes the importance of removal records for product safety, prepares personnel to consistently and correctly determine when a removal record is needed, and ensures that a removal record is generated when required.
- Develop a structured on-the-job training program that identifies and defines tasks necessary for manufacturing personnel to be considered fully qualified in their job series and includes a grading system for trainers and trainees to track progress and determine competence.
- Document and archive the results of training provided and received as part of the program recommended to support future data analysis.
- Revise Boeing’s safety risk management process to ensure that it 1) identifies the root causes of manufacturing process compliance issues, like the persistent deficiencies with parts removal and other production process inconsistencies identified in this investigation, and 2) evaluates the effectiveness of corrective actions.
- As Boeing integrates its quality management system and safety management system, develop a process that can identify escapes that result from human error, assess them using a system specifically designed to identify factors that contribute to such errors, and implement effective mitigation strategies.
The report contains recommendations for the FAA as well, such as issuing “an airworthiness directive to require that all in-service MED plug-equipped airplanes be retrofitted with the design enhancement” and a revision of compliance enforcement surveillance systems to “ensure that it provides the necessary functionality for Federal Aviation Administration managers and inspectors overseeing production approval holders to effectively identify, record, track, and resolve recurring and systemic discrepancies and nonconformance issues, including those related to specific manufacturing processes.”
During the hearing, it was noted that the cockpit voice recorder (CVR) was not preserved after the accident, as one board member noted the focus of the crew was on the safety of the passengers, not pulling the circuit breaker that would have prevented the automatic overwriting of the recording.
Other recommendations for the FAA:
- Require all newly manufactured airplanes that must have a CVR be fitted with one capable of recording the last 25 hours of audio.
- Require retrofit of all CVRs on all airplanes required to carry both a CVR and a flight data recorder (FDR) with a CVR capable of recording the last 25 hours of audio.
- Conduct a study to determine the factors that affect caregivers’ decisions about the use of child restraint systems (CRSs) when traveling on a Title 14 Code of Federal Regulations Part 121 air carrier airplane with children under the age of 2 and to understand the challenges associated with using CRSs. Publish the study findings.
- Use the study findings to direct the FAA’s efforts to increase child restraint system usage.
